Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth: A nationwide cohort study in Denmark and Sweden.

BACKGROUND: The prevalence of depression and the exposure to antidepressants are high among women of reproductive age and during pregnancy. Duloxetine is a selective serotonin-norepinephrine reuptake inhibitor (SNRI) approved in the United States and Europe in 2004 for the treatment of depression. Fetal safety of duloxetine is not well established. The present study evaluates the association of exposure to duloxetine during pregnancy and the risk of major and minor congenital malformations and the risk of stillbirths. METHODS AND
FINDINGS: A population-based observational study was conducted based on data from registers in Sweden and Denmark. All registered births and stillbirths in the medical birth registers between 2004 and 2016 were included. Malformation diagnoses were identified up to 1 year after birth. Logistic regression analyses were used. Potential confounding was addressed through multiple regression, propensity score (PS) matching, and sensitivity analyses. Confounder variables included sociodemographic information (income, education, age, year of birth, and country), comorbidity and comedication, previous psychiatric contacts, and birth-related information (smoking during pregnancy and previous spontaneous abortions and stillbirths). Duloxetine-exposed women were compared with 4 comparators: (1) duloxetine-nonexposed women; (2) selective serotonin reuptake inhibitor (SSRI)-exposed women; (3) venlafaxine-exposed women; and (4) women exposed to duloxetine prior to, but not during, pregnancy. Exposure was defined as redemption of a prescription during the first trimester and throughout pregnancy for the analyses of malformations and stillbirths, respectively. Outcomes were major and minor malformations and stillbirths gathered from the national patient registers. The cohorts consisted of more than 2 million births with 1,512 duloxetine-exposed pregnancies. No increased risk for major malformations, minor malformations, or stillbirth was found across comparison groups in adjusted and PS-matched analyses. Duloxetine-exposed versus duloxetine-nonexposed PS-matched analyses showed odds ratio (OR) 0.98 (95% confidence interval [CI] 0.74 to 1.30, p = 0.909) for major malformations, OR 1.09 (95% CI 0.82 to 1.45, p = 0.570) for minor malformation, and 1.18 (95% CI 0.43 to 3.19, p = 0.749) for stillbirths. For the individual malformation subtypes, some findings were statistically significant but were associated with large statistical uncertainty due to the extremely small number of events. The main limitations for the study were that the indication for duloxetine and a direct measurement of depression severity were not available to include as covariates.
CONCLUSIONS: Based on this observational register-based nationwide study with data from Sweden and Denmark, no increased risk of major or minor congenital malformations or stillbirth was associated with exposure to duloxetine during pregnancy.

Introduction

Depression or depressive symptoms are common during pregnancy [1-4]. Despite a drop in recent years [5], the use of antidepressants among pregnant women has grown steadily [6-12]. Selective serotonin reuptake inhibitors (SSRIs) are the most common [9,12,13], followed by serotonin and norepinephrine reuptake inhibitors (SNRIs) [5,12,14].

Duloxetine (an SNRI) was approved in the United States and Europe in 2004. In Europe, the indication is for major depressive disorder, generalized anxiety disorder, stress urinary incontinence, and diabetic peripheral neuropathy. A common indication for women of childbearing age is for depressive disorder [15]. The safety of antidepressants during pregnancy, especially their teratogenic effect, has been uncertain [16-20]. However, studies that address potential confounding report no association between first trimester exposure to SSRIs and malformation [21] or stillbirth [22,23]. This is not necessarily applicable to SNRIs, since they affect also norepinephrine levels [24]. Studies on SNRIs suggest no increased risk of major malformation, based on postmarketing surveillance systems [25-27], small cohorts without a comparison group [28,29], or cohorts with a comparison group [30-32]. A recent review found no increased risk of major malformations but concluded that the evidence for duloxetine is limited [33]. A large cohort study is necessary to assess the risk of rare outcomes (e.g., malformations, stillbirth).

The present study evaluates the association between duloxetine exposure during pregnancy and the risk of major and minor congenital malformation and stillbirths in a cohort based on all pregnancies in Sweden and Denmark between 2004 and 2016.

Methods

The present study is based on a safety study regarding duloxetine and pregnancy outcomes, with the protocol and the full study report available via the European Network of Centres for Pharmacoepidemiology and Pharmacovigilance (ENCePP, EUPAS20253) [34]. Beside malformation and stillbirth, the protocol and full study include abortion, preterm birth, and being born small for gestational age (SGA) as outcomes. Results about abortion is published elsewhere [35], and results about preterm birth and SGA is under preparation for publication.

The study is based on nationwide registers from Sweden and Denmark covering all registered births from 2004 to 2016, with 1-year follow-up data of congenital malformations. Registers were linked with unique personal identification numbers given to all Swedish and Danish citizens upon birth or immigration. The following Danish and Swedish nationwide registers were used. The prescription registers [36-38], containing electronically submitted information on prescriptions dispensed by pharmacies, classified according to the global ATC system. The patient registers [39,40] that include discharge diagnoses of all inpatients and outpatients in contact with a hospital. The medical birth registers [41-43] were all live births as well as stillbirths from varying gestational ages in the different countries are notified to the registers with information on the mother, the neonate, and the father as well. Registers holding information about education and household income [44-46] based on national statistics on education (highest obtained education) and annual tax reports.

The study was approved by the Swedish regional ethics review board in Gothenburg (ref: 1040–17 and T782-18), the Swedish National Board of Health and Welfare (ref: 30714/2017), and in Denmark by the Data Protection Agency (j.nr. VD-2018-371, I-Suite nr. 6621). No approval from the Danish Research Ethics Committees for the Capital Region was needed since only national registers were used.

Cohorts

The cohort consisted of registered live and stillbirths from 2004 to 2016 of women with a valid personal identification number aged 18 and above. Exclusion criteria for the malformation analyses were the following: mothers migrating between 365 days prior to last menstrual period (LMP) until 365 days postdelivery, stillbirths, invalid personal identification number of offspring, births with a chromosomal abnormality diagnosis (ICD-10 codes Q87.1, Q87.4, Q9X), and mothers with a redeemed prescription for a teratogenic drug in the period from LMP to 90 days post LMP (warfarin [ATC: B01AA03], antineoplastic agents [ATC: L01], isotretinoin [ATC: D10AD04, D10BA01, D10AD54], misoprostol [ATC: A02BB01, G02AD06, M01AE56], lithium [ATC: N05AN01], and thalidomide [ATC: L04AX02]). Exclusion criteria for the stillbirth analyses were the following: mothers migrated between 90 days prior to LMP until delivery and gestational age shorter than 22 weeks or longer than 45 weeks.

Exposure, comparison groups, and outcome

Maternal exposure to medication was defined as a redeemed prescription at a pharmacy. The exposure time window for malformations was from LMP to 90 days after LMP, corresponding to the first trimester of the pregnancy. The exposure time window for stillbirth was from LMP to end of pregnancy. With maternal exposure, fetal exposure is assumed.

Duloxetine exposure was defined as at least one redeemed prescription of duloxetine (ATC N06AX21) in the exposure time window. Four comparison groups were used, all with no redeemed prescription of duloxetine in the relevant exposure time window: (1) duloxetine nonexposed: no redeemed prescription of duloxetine in the exposure time window; (2) SSRI exposed: at least one redeemed prescription of an SSRI (ATC N06AB) in the exposure time window; (3) venlafaxine exposed: at least one redeemed prescription of venlafaxine (ATC N06AX16. Venlafaxine is an SNRI like duloxetine) in the exposure time window; and (4) duloxetine discontinuers: at least one redeemed prescription of duloxetine between 365 days prior to LMP to LMP and not during pregnancy. SSRI-exposed and venlafaxine-exposed women and duloxetine discontinuers were used as comparators to take confounding by indication and severity, and maybe even unmeasured confounding, into account, as they are expected to be similar to duloxetine-exposed women with regard to, e.g., the underlying psychological disease, comorbidity, and health behavior. The comparison groups were not mutually exclusive, and comparisons were analyzed separately with each comparison group. For both the malformation and the stillbirth analyses, an additional exclusion criterion was applied when comparing duloxetine-exposed women with duloxetine nonexposed, SSRI exposed, and venlafaxine exposed: women with duloxetine exposure from 90 days prior to LMP but no exposure from LMP to 90 days after LMP were excluded. This washout period was applied to avoid misclassification.

Major and minor malformations were classified according to the EUROCAT classification of congenital malformations version 1.4 [47]. Diagnoses of the offspring were gathered from the national patient registers as either a primary or secondary diagnosis registered within 365 days after birth. Major malformations were defined as the following ICD-10 codes: Q-chapter, D215, D821, D1810, P350, P351, P371, except for the ICD-10 codes used to define minor malformations. Minor malformations were defined as the ICD-10 codes in Table A in S1 Tables. Also, analyses of major malformation subtypes were performed: abdominal wall; cardiac; digestive system; ear, face, and neck; eye; genital; limb; nervous system; orofacial clefts; respiratory system; urinary system; and other anomalies (Table B in S1 Tables). Information on stillbirth was gathered from the medical birth registers and was defined as no signs of life at birth after week 22 of pregnancy and from the patient register if abortions were registered after week 22 [48].

Statistical methods

For each of the 4 comparator groups, an unadjusted, an adjusted multiple regression, and a propensity score (PS)-matched analysis were performed.

The PSs were estimated with logistic regression and greedy matching using the SAS macro OneToManyMTCH [49] with an extension to secure only women with a difference of maximum of 0.2 logit of the PS were used to match. When matching duloxetine exposed with duloxetine nonexposed, a 1:4 ratio was used. Because of limited data in the other comparison groups, duloxetine and SSRI exposed were matched with a 1:2 ratio and venlafaxine exposed and duloxetine discontinuers with a 1:1 ratio. Duloxetine-exposed individuals with no match were excluded from the PS-matched analyses. After PS matching, a conditional logistic regression, including the matched group id as a strata variable, was fitted to assess risk of minor and major malformations and stillbirths, respectively. To assess the balance of possible confounders after PS matching, standardized differences were calculated using the SAS macro stddiff macro [50].

For the adjusted multiple regression and the PS, prespecified covariates were used based on previous publications [21,23] and available data. When fitting each model, covariates were removed, if the model could not be estimated. This is the case if, e.g., no patients in one exposure group had any severe stress reaction. Then, the variable severe stress reaction cannot be part of the model and the covariate needs to be removed.

Covariates used for the malformation and stillbirth analyses are the following: data source (Sweden/Denmark), birth year of the offspring (3 categories: 2004 to 2008, 2009 to 2012, and 2013 to 2016), maternal age (4 categories: 18 to 24, 25 to 29, 30 to 34, and >34 years), previous spontaneous abortions (0/1/≥2), previous stillbirths (yes/no), smoking during pregnancy (yes/no), psychiatric hospitalizations (1 year prior to LMP: yes/no), psychiatric outpatient visits (1 year prior to LMP: yes/no), household income (year of LMP, grouped in quartiles), and highest completed education (year of LMP, 3 categories: <11, 11 to 15, and >15 years). Comorbidities (identified up to maximum 5 years prior to LMP; see Table C in S1 Tables for ICD-10 codes and ATC codes): affective disorder, anxiety or phobia, depression, diabetes during pregnancy, diabetes, diabetic peripheral neuropathy, hyperthyroidism and hypothyroidism, hypertension, obesity, renal failure, severe stress reaction, and stress urinary incontinence. Comedication (at least one redeemed prescription between 90 days prior to LMP to end of the relevant exposure time window; see Table D in S1 Tables for ATC codes): antiepileptics, antihypertensives, antipsychotics, anxiolytics, danazol, estradiol, fluconazole, glucose-lowering, NSAID, opioids, progesterone, steroid hormone, thyroid hormone, and triptans. SSRI and venlafaxine comedication were not part of the confounder selection, since these will be highly associated with the comparison group rather than the duloxetine exposed. For a complete list of covariates used for the individual analysis, see Table E in S1 Tables.

In general, there were very few missing values. If income was missing at year of LMP, first income was imputed from 1 year prior to LMP, and, if still missing, income was imputed from 1 year after LMP, where possible. If education was missing at year of LMP, it was imputed from 1 year after LMP, where possible. Data were analyzed assuming missing at random and persons with missing values were deleted from the analysis.

For the analyses of stillbirth and malformation subtypes with less than 30 outcome events in the exposed group, only unadjusted and PS-matched analyses were performed.

Four prespecified sensitivity analyses were conducted. To assess the exposure definition of minimum one redeemed prescription and evaluate potential misclassification of exposure, sensitivity analyses were conducted with (1) exposure redefined to minimum 2 redeemed prescriptions; and (2) exposure redefinition to overlap between the exposure time window and days’ supply of redeemed prescriptions. Days’ supply was based on the number and strength of redeemed pills compared with the WHO’s daily defined dose [51]. A woman’s first pregnancy may influence later pregnancies; therefore, sensitivity analyses (3) restricting the cohort to the first pregnancy within the study period were performed. The medical birth registers hold information on maternal BMI, but this is expected to be missing for a substantial number of women. The main analyses did not include BMI as a covariate, but (4) sensitivity analyses including BMI as covariate were conducted. The sensitivity analyses handled BMI as missing at random, although this may not be fully accurate.

SAS Enterprise Guide 7.15 was used, and a significance level of 5% was applied. Validation of the programming was performed; smaller programs (3 to 20 lines of coding) were reviewed, and longer programs were double coded by an independent statistical programmer. This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (see S1 Checklist). The protocol was developed prior to data access and followed, with a few exceptions: (1) Incomes should have been standardized to 2015-year level, but when grouped in quartiles, stratified on calendar year, standardization was not needed. (2) ATC codes were included to identify comorbidity, although not described in the protocol. Utilizing both ICD-10 and ATC codes more women with the given comorbidities will be identified. (3) Comedication should have been identified 1 year prior to LMP but was changed to comedication during the relevant exposure time window, since it is more likely that comedication during pregnancy will affect the outcomes of malformation and stillbirth and therefore act as confounders.

Results

The final cohorts included up to 2,132,163 pregnancies. Among these, 1,512 and 1,668 were duloxetine exposed in the analyses of malformation and stillbirth, respectively. See flow chart in Fig 1. Up to 80,760, 64,594, and 7,699 events of major malformation, minor malformation, and stillbirth, respectively, were included in the analyses. Tables 1 and 2 show baseline characteristics for the analyses of malformation and stillbirth, respectively (Tables F and G in S1 Tables show baseline characteristics for all covariates). Table H in S1 Tables shows number of events per thousand pregnancies. Missing values ranged from 0.4% to 3.5% for household income, education, smoking, and birth order. BMI had 6.4% missing values.

Fig 1

Flow chart for the cohorts used to analyze malformations and stillbirth.

The 73 stillbirths identified in the patient registers were all registered as spontaneous abortions after week 22. Exposure time window for malformations: from LMP to 90 days after LMP. Exposure time window for stillbirth: from LMP to end of pregnancy. LMP, last menstrual period; SSRI, selective serotonin reuptake inhibitor.

Table 1

Baseline characteristics for the analyses of malformation.

Variable	Value	Duloxetine Before matching n = 1,512	Duloxetine vs. duloxetine nonexposed					Duloxetine vs. SSRI					Duloxetine vs. venlafaxine					Duloxetine vs. duloxetine discontinuers
			Before matching		After matching			Before matching		After matching			Before matching		After matching			Before matching		After matching
			Duloxetine nonexposed n = 2,074,652	Std mean diff.	Duloxetine n = 1,438	Duloxetine nonexposed n = 5,751	Std mean diff.	SSRI n = 39,959	Std mean diff.	Duloxetine n = 1,437	SSRI n = 2,874	Std mean diff.	Venlafaxine n = 5,240	Std mean diff	Duloxetine n = 1,429	Venlafaxine n = 1,429	Std mean diff	Duloxetine discontinuers n = 2,876	Std mean diff	Duloxetine n = 1,434	Discontinuers n = 1,435	Std mean diff
Age, continuous	Mean, y	31 (27;35)	30 (27;34)	0.15	30.7 (27.2;35.0)	30.8 (26.8;34.7)	0.04	31 (27;34)	0.08	30.7 (27.2;35.0)	30.4 (26.6;34.5)	0.08	31 (26;35)	0.09	30.7 (27.2;35.0)	30.4 (26.3;34.6)	0.07	30 (27;34)	0.11	30.7 (27.2;35.0)	30.5 (26.7;34.7)	0.04
Age, grouped	18–24 y	231 (15.3%)	323,541 (15.6%)	0.16	222 (15.4%)	888 (15.4%)	0.05	6,399 (16.0%)	0.06	222 (15.4%)	469 (16.3%)	0.04	947 (18.1%)	0.09	222 (15.5%)	240 (16.8%)	0.03	470 (16.3%)	0.07	222 (15.5%)	230 (16.0%)	0.05
	25–29 y	447 (29.6%)	684,195 (33.0%)		429 (29.8%)	1,659 (28.8%)		11,740 (29.4%)		428 (29.8%)	887 (30.9%)		1,488 (28.4%)		424 (29.7%)	429 (30.0%)		914 (31.8%)		427 (29.8%)	435 (30.3%)
	30–34 y	379 (25.1%)	591,115 (28.5%)		359 (25.0%)	1,532 (26.6%)		10,855 (27.2%)		359 (25.0%)	704 (24.5%)		1,359 (25.9%)		356 (24.9%)	364 (25.5%)		710 (24.7%)		359 (25.0%)	336 (23.4%)
	35–60 y	455 (30.1%)	475,801 (22.9%)		428 (29.8%)	1,672 (29.1%)		10,965 (27.4%)		428 (29.8%)	814 (28.3%)		1,446 (27.6%)		427 (29.9%)	396 (27.7%)		782 (27.2%)		426 (29.7%)	434 (30.2%)
Household income	Quartile1	569 (37.8%)	458,644 (22.2%)	0.41	549 (38.2%)	2,189 (38.1%)	0.00	12,032 (30.3%)	0.19	548 (38.1%)	1,115 (38.8%)	0.03	1,895 (36.4%)	0.05	545 (38.1%)	569 (39.8%)	0.05	1,051 (36.7%)	0.05	549 (38.3%)	560 (39.0%)	0.05
	Quartile2	391 (25.9%)	514,943 (25.0%)		370 (25.7%)	1,481 (25.8%)		10,306 (26.0%)		370 (25.7%)	757 (26.3%)		1,418 (27.3%)		367 (25.7%)	369 (25.8%)		815 (28.5%)		367 (25.6%)	346 (24.1%)
	Quartile3	317 (21.0%)	547,822 (26.6%)		300 (20.9%)	1,222 (21.2%)		9,760 (24.6%)		300 (20.9%)	610 (21.2%)		1,106 (21.3%)		298 (20.9%)	280 (19.6%)		597 (20.9%)		300 (20.9%)	317 (22.1%)
	Quartile4	230 (15.3%)	540,500 (26.2%)		219 (15.2%)	859 (14.9%)		7,557 (19.1%)		219 (15.2%)	392 (13.6%)		784 (15.1%)		219 (15.3%)	211 (14.8%)		399 (13.9%)		218 (15.2%)	212 (14.8%)
Education	<11 y	341 (22.7%)	252,162 (12.3%)	0.40	327 (22.7%)	1,462 (25.4%)	0.05	7,390 (18.6%)	0.19	327 (22.8%)	685 (23.8%)	0.03	1,221 (23.5%)	0.06	324 (22.7%)	309 (21.6%)	0.03	714 (25.0%)	0.06	325 (22.7%)	301 (21.0%)	0.05
	11–15 y	806 (53.7%)	1,000,210 (48.8%)		771 (53.6%)	3,010 (52.3%)		19,650 (49.5%)		770 (53.6%)	1,540 (53.6%)		2,641 (50.9%)		765 (53.5%)	774 (54.2%)		1,452 (50.8%)		770 (53.7%)	791 (55.1%)
	>16 y	355 (23.6%)	797,606 (38.9%)		340 (23.6%)	1,279 (22.2%)		12,630 (31.8%)		340 (23.7%)	649 (22.6%)		1,326 (25.6%)		340 (23.8%)	346 (24.2%)		692 (24.2%)		339 (23.6%)	343 (23.9%)
Smoking	Yes	301 (20.7%)	179,398 (9.0%)	0.34	298 (20.7%)	1,339 (23.3%)	−0.06	6,640 (17.2%)	0.09	297 (20.7%)	570 (19.8%)	0.02	1,303 (25.6%)	−0.12	296 (20.7%)	272 (19.0%)	0.04	578 (20.9%)	−0.01	296 (20.6%)	285 (19.9%)	0.02
Data source, Sweden	Yes	1,010 (66.8%)	1,324,668 (63.9%)	0.06	959 (66.7%)	3,900 (67.8%)	−0.02	2,5975 (65.0%)	0.03	958 (66.7%)	1,881 (65.4%)	0.03	2,948 (56.3%)	0.22	950 (66.5%)	960 (67.2%)	−0.01	1,821 (63.3%)	0.07	955 (66.6%)	950 (66.2%)	0.01
Previous stillbirth	Yes	6 (0.4%)	10,401 (0.5%)	−0.02	6 (0.4%)	76 (1.3%)	−0.10	250 (0.6%)	0.02	6 (0.4%)	8 (0.3%)	0.02	22 (0.4%)	0.00	6 (0.4%)	6 (0.4%)	0.00	17 (0.6%)	−0.03	6 (0.4%)	5 (0.3%)	0.01
Depression	Yes	517 (34.2%)	39,131 (1.9%)	0.93	486 (33.8%)	2,082 (36.2%)	−0.05	7,326 (18.3%)	0.37	485 (33.8%)	1002 (34.9%)	−0.02	1,324 (25.3%)	0.20	478 (33.4%)	509 (35.6%)	−0.05	812 (28.2%)	0.13	482 (33.6%)	477 (33.2%)	0.01
Anxiety or phobia	Yes	193 (12.8%)	19,287 (0.9%)	0.48	181 (12.6%)	769 (13.4%)	−0.02	4,022 (10.1%)	0.08	181 (12.6%)	341 (11.9%)	0.02	508 (9.7%)	0.10	177 (12.4%)	202 (14.1%)	−0.05	327 (11.4%)	0.04	180 (12.6%)	162 (11.3%)	0.04
Severe stress reaction	Yes	171 (11.3%)	21,233 (1.0%)	0.44	153 (10.6%)	576 (10.0%)	0.02	2,010 (5.0%)	0.23	153 (10.6%)	296 (10.3%)	0.01	353 (6.7%)	0.16	149 (10.4%)	158 (11.1%)	−0.02	278 (9.7%)	0.05	151 (10.5%)	137 (9.5%)	0.03
Stress urinary incontinence	Yes	<5 (0%)	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00
SSRI comedication	Yes	<5 (0%)	39,959 (1.9%)	−0.20	<5 (0%)	923 (16.0%)	−0.62	N/A	N/A	N/A	N/A	N/A	710 (13.5%)	−0.56	<5 (0%)	185 (12.9%)	−0.55	579 (20.1%)	−0.71	<5 (0%)	302 (21.0%)	−0.73
Venlafaxine comedication	Yes	<5 (0%)	5,240 (0.3%)	−0.07	<5 (0%)	173 (3.0%)	−0.25	710 (1.8%)	−0.19	<5 (0%)	71 (2.5%)	−0.23	N/A	N/A	N/A	N/A	N/A	88 (3.1%)	−0.25	<5 (0%)	49 (3.4%)	−0.27

Previous stillbirth, depression, anxiety or phobia, and severe stress reaction were defined as diagnoses up to 5 years prior to LMP. PS-matched models were based on covariates covering comorbidity (up to 5 years prior to LMP), comedication (during the relevant time period), hospital contacts, education, and income. For the complete list for the individual analyses, see Table E in S1 Tables. SSRI and venlafaxine comedication were not part of the confounder variables.

LMP, last menstrual period; PS, propensity score; SSRI, selective serotonin reuptake inhibitor; Std mean diff, standardized mean difference; y, years.

Table 2

Baseline characteristics for the analyses of stillbirth.

Variable	Value	Duloxetine Before matching n = 1,668	Duloxetine vs. duloxetine nonexposed					Duloxetine vs. SSRI					Duloxetine vs. venlafaxine					Duloxetine vs. duloxetine discontinuers
			Before matching		After matching			Before matching		After matching			Before matching		After matching			Before matching		After matching
			Duloxetine nonexposed n = 2,130,495	Std mean diff.	Duloxetine n = 1,581	Duloxetine nonexposed n = 6,324	Std mean diff.	SSRI n = 54,792	Std mean diff.	Duloxetine n = 1,585	SSRI n = 3,170	Std mean diff.	Venlafaxine n = 6,005	Std mean diff	Duloxetine n = 1,580	Venlafaxine n = 1,580	Std mean diff	Duloxetine discontinuers n = 2,815	Std mean diff	Duloxetine n = 1,559	Discontinuers n = 1,561	Std mean diff
Age, continuous	Mean, y	31.0 (27.3;35.1)	30.2 (26.7;33.6)	0.18	30.9 (27.3;35.1)	30.9 (26.6;35.0)	0.05	30.7 (26.8;34.4)		30.9 (27.3;35.1)	30.7 (26.9;34.9)	0.05	30.6 (26.6;34.6)		30.9 (27.3;35.1)	30.6 (26.9;35.1)	0.02	30.3 (26.6;34.3)		30.9 (27.3;35.1)	30.8 (27.0;34.7)	0.04
Age, grouped	18–24 y	245 (14.7%)	335,954 (15.8%)	0.16	235 (14.9%)	1,087 (17.2%)	0.07	8,706 (15.9%)		236 (14.9%)	464 (14.6%)	0.05	1,038 (17.3%)		235 (14.9%)	227 (14.4%)	0.03	470 (16.7%)		236 (15.1%)	231 (14.8%)	0.00
	25–29 y	485 (29.1%)	702,496 (33.0%)		466 (29.5%)	1,723 (27.2%)		16,148 (29.5%)		467 (29.5%)	973 (30.7%)		1,720 (28.6%)		466 (29.5%)	477 (30.2%)		893 (31.7%)		460 (29.5%)	466 (29.9%)
	30–34 y	426 (25.5%)	604,784 (28.4%)		398 (25.2%)	1,529 (24.2%)		14,876 (27.1%)		400 (25.2%)	769 (24.3%)		1,566 (26.1%)		398 (25.2%)	390 (24.7%)		692 (24.6%)		391 (25.1%)	395 (25.3%)
	35–60 y	512 (30.7%)	487,539 (22.9%)		482 (30.5%)	1,985 (31.4%)		15,067 (27.5%)		482 (30.4%)	964 (30.4%)		1,684 (28.0%)		481 (30.4%)	486 (30.8%)		762 (27.1%)		472 (30.3%)	467 (30.0%)
Household income	Quartile1	627 (37.7%)	481,338 (22.8%)	0.39	601 (38.0%)	2,371 (37.5%)	0.04	16,538 (30.4%)		605 (38.2%)	1,232 (38.9%)	0.03	2,172 (36.4%)		603 (38.2%)	606 (38.4%)	0.06	1,031 (36.8%)		595 (38.2%)	603 (38.7%)	0.03
	Quartile2	427 (25.7%)	529,514 (25.1%)		402 (25.4%)	1,544 (24.4%)		14,121 (26.0%)		402 (25.4%)	793 (25.0%)		1,617 (27.1%)		401 (25.4%)	423 (26.8%)		806 (28.8%)		396 (25.4%)	393 (25.2%)
	Quartile3	353 (21.2%)	554,446 (26.2%)		334 (21.1%)	1,406 (22.2%)		13,320 (24.5%)		334 (21.1%)	677 (21.4%)		1,261 (21.1%)		333 (21.1%)	331 (20.9%)		578 (20.6%)		326 (20.9%)	327 (21.0%)
	Quartile4	255 (15.3%)	547,490 (25.9%)		244 (15.4%)	1,003 (15.9%)		10,383 (19.1%)		244 (15.4%)	468 (14.8%)		913 (15.3%)		243 (15.4%)	220 (13.9%)		388 (13.8%)		242 (15.5%)	236 (15.1%)
Education	<11 y	374 (22.6%)	262,602 (12.5%)	0.35	601 (38.0%)	1,617 (25.6%)	0.07	10,068 (18.5%)		360 (22.7%)	707 (22.3%)	0.03	1,386 (23.3%)		357 (22.6%)	333 (21.1%)	0.05	708 (25.3%)		355 (22.8%)	348 (22.3%)	0.03
	11–15 y	878 (53.1%)	1,020,571 (48.6%)		402 (25.4%)	3,191 (50.5%)		26,933 (49.6%)		840 (53.0%)	1,703 (53.7%)		2,995 (50.5%)		838 (53.0%)	868 (54.9%)		1,425 (50.9%)		824 (52.9%)	842 (54.0%)
	>16 y	402 (24.3%)	816,010 (38.9%)		334 (21.1%)	1,516 (24.0%)		17,306 (31.9%)		385 (24.3%)	760 (24.0%)		1,555 (26.2%)		385 (24.4%)	379 (24.0%)		667 (23.8%)		380 (24.4%)	369 (23.7%)
Smoking	Yes	336 (20.9%)	183,149 (8.9%)	0.34	332 (21.0%)	1,447 (22.9%)	−0.05	9,011 (17.0%)		332 (20.9%)	661 (20.9%)	0.00	1,469 (25.3%)		331 (20.9%)	321 (20.3%)	0.02	560 (20.7%)		324 (20.8%)	316 (20.3%)	0.01
Data source, Sweden	Yes	1,120 (67.1%)	1,360,775 (63.9%)	0.07	1,059 (67.0%)	4,293 (67.9%)	−0.02	36,616 (66.8%)		1,063 (67.1%)	2,086 (65.8%)	0.03	3,414 (56.8%)		1,058 (67.0%)	1,084 (68.6%)	−0.04	1,770 (62.8%)		1,040 (66.7%)	1,007 (64.6%)	0.04
Previous stillbirth	Yes	6 (0.4%)	10,898 (0.5%)	−0.02	6 (0.4%)	90 (1.4%)	−0.11	339 (0.6%)		6 (0.4%)	10 (0.3%)	0.01	29 (0.5%)		6 (0.4%)	8 (0.5%)	−0.02	19 (0.7%)		6 (0.4%)	5 (0.3%)	0.01
Depression	Yes	1,090 (65.3%)	2,091,153 (98.1%)	0.94	541 (34.2%)	2,342 (37.0%)	−0.06	9,984 (18.2%)		545 (34.4%)	1,129 (35.6%)	−0.03	1,529 (25.4%)		540 (34.2%)	572 (36.2%)	−0.04	775 (27.5%)		524 (33.6%)	525 (33.7%)	0.00
Anxiety or phobia	Yes	217 (13.0%)	19,510 (0.9%)	0.49	202 (12.8%)	811 (12.8%)	−0.00	5,348 (9.8%)		205 (12.9%)	442 (13.9%)	−0.03	575 (9.6%)		202 (12.8%)	210 (13.3%)	−0.02	312 (11.1%)		194 (12.4%)	50 (3.2%)	0.01
Severe stress reaction	Yes	203 (12.2%)	21,580 (1.0%)	0.46	181 (11.4%)	679 (10.7%)	0.02	2,815 (5.1%)		184 (11.6%)	363 (11.5%)	0.00	399 (6.6%)		180 (11.4%)	176 (11.1%)	0.01	260 (9.2%)		173 (11.1%)	175 (11.2%)	0.00
Stress urinary incontinence	Yes	<5 (0%)	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00	<5 (0%)	0.00	<5 (0%)	<5 (0%)	0.00
SSRI comedication	Yes	<5 (0%)	54,797 (2.6%)	−0.23	<5 (0%)	1,219 (19.3%)	−0.69	N/A	N/A	N/A	N/A	N/A	1,255 (20.9%)	−0.73	<5 (0%)	322 (20.4%)	−0.72	778 (27.6%)	−0.87	<5 (0%)	472 (30.3%)	−0.93
Venlafaxine comedication	Yes	<5 (0%)	6,008 (0.3%)	−0.08	<5 (0%)	249 (3.9%)	−0.29	1,255 (2.3%)	−0.22	<5 (0%)	107 (3.4%)	−0.26	N/A	N/A	N/A	N/A	N/A	95 (3.4%)	−0.26	<5 (0%)	59 (3.8%)	−0.28

Previous stillbirth, depression, anxiety or phobia, and severe stress reaction were defined as diagnoses up to 5 years prior to LMP. PS-matched models were based on covariates covering comorbidity (up to 5 years prior to LMP), comedication (during the relevant time period), hospital contacts, education, and income. For the complete list for the individual analyses, see Table E in S1 Tables. SSRI and venlafaxine comedication were not part of the confounder variables.

LMP, last menstrual period; PS, propensity score; SSRI, selective serotonin reuptake inhibitor; Std mean diff, standardized mean difference; y, years.

For major malformations, all odds ratio (OR) point estimates based on unadjusted, adjusted, or PS-matched analyses across all 4 comparator groups are centered around 1, suggesting no increased risk (Fig 2). The PS-matched analyses for duloxetine exposed compared with duloxetine nonexposed yielded an OR of 0.98 (95% confidence interval [CI] 0.74 to 1.30, p = 0.909); for SSRI exposed, 1.07 (95% CI 0.78 to 1.46, p = 0.688); for venlafaxine exposed, 0.95 (95% CI 0.66 to 1.36, p = 0.783); and for duloxetine discontinuers, 0.80 (95% CI 0.56 to 1.14, p = 0.213). The sensitivity analyses for major malformation the OR and 95% CI also centered around 1 and suggested no increased risk (Table I in S1 Tables).

Fig 2

Risk of major and minor malformation.

Duloxetine vs 4 comparators. Odds ratio for major or minor malformations for duloxetine vs comparator. Exposure definition: ≥1 redeemed prescription. Adjusted and PS-matched models were based on covariates covering comorbidity (up to 5 years prior to LMP), comedication (90 days prior to LMP to end of the relevant exposure time window), hospital contacts, education, and income. For the complete list of covariates for the individual analyses, see Table E in S1 Tables. CI, Wald 95% confidence intervals; LMP, last menstrual period; N, number of observations in analyses; PS-matched, propensity score–matched analyses based on conditional logistic regression; SSRI, selective serotonin reuptake inhibitor.

For minor malformations, the unadjusted analysis of duloxetine exposed compared with duloxetine nonexposed showed an increased risk. However, in the adjusted and PS-matched analyses, the risk was lower and showed no statistically significant increase. When compared with SSRI exposed, venlafaxine exposed, and duloxetine discontinuers, some point estimates indicate an increased risk for minor malformations for duloxetine exposed; however, the wide CIs suggest great uncertainty (Fig 2). The PS-matched analysis for duloxetine exposed compared with duloxetine nonexposed was OR 1.09 (95% CI 0.82 to 1.45, p = 0.570); for SSRI exposed, 1.39 (95% CI 1.00 to 1.94, p = 0.048); for venlafaxine exposed, 1.20 (95% CI 0.82 to 1.76, p = 0.337); and for duloxetine discontinuers, 1.11 (95% CI 0.77 to 1.60, p = 0.574). The sensitivity analyses for minor malformation also suggested no increased risk (Table J in S1 Tables).

For the individual major malformation subtypes, all analyses were associated with large statistical uncertainty. Some point estimates suggested increased risk but were inconclusive. Results for the major malformation subtypes are found in the Supporting information (both main and sensitivity analyses; Tables K-V in S1 Tables). For cardiac malformations, PS-matched analysis for duloxetine exposed compared with duloxetine nonexposed was OR 1.01 (95% CI 0.64 to 1.60, p = 0.962); for SSRI exposed, 0.79 (95% CI 0.49 to 1.29, p = 0.344); for venlafaxine exposed, 0.78 (95% CI 0.44 to 1.38, p = 0.388); and for duloxetine discontinuers, 0.92 (95% CI 0.51 to 1.63, p = 0.768). It is of note that a statistically significant increased risk of “other anomalies and syndromes” was found when duloxetine-exposed women were compared with SSRI exposed (PS-matched analyses of duloxetine versus SSRI: OR 2.43 [95% CI 1.10 to 5.38, p = 0.028]). See Table B in S1 Tables for the full list of other anomalies and syndromes, but it includes, e.g., craniosynostosis, situs inversus, and fetal alcohol syndrome.

For stillbirths, the analyses suggested no increased risk for duloxetine exposed across all comparison groups, although the CIs were wide (Fig 3). PS-matched analysis for duloxetine exposed compared with duloxetine nonexposed was 1.18 (95% CI 0.43 to 3.19, p = 0.749); for SSRI exposed, 0.63 (95% CI 0.23 to 1.71, p = 0.359); for venlafaxine exposed, 0.42 (95% CI 0.15 to 1.18, p = 0.100); and for duloxetine discontinuers, 0.83 (95% CI 0.25 to 2.73, p = 0.763). The sensitivity analyses for stillbirth also suggested no increased risk (Table W in S1 Tables).

Fig 3

Risk of stillbirth.

Duloxetine vs 4 comparators. Odds ratio for stillbirth for duloxetine vs comparator. Exposure definition: ≥1 redeemed prescription. PS-matched models were based on covariates covering comorbidity (up to 5 years prior to LMP), comedication (90 days prior to LMP to end of the relevant exposure time window), hospital contacts, education, and income. For the complete list of covariates for the individual analyses, see Table E in S1 Tables. CI, Wald 95% confidence intervals; LMP, last menstrual period; N, number of observations in analyses; PS-matched, propensity score–matched analyses based on conditional logistic regression; SSRI, selective serotonin reuptake inhibitor.

Discussion

This observational study with nationwide register data from Sweden and Denmark found no increased risk of congenital minor or major malformations or stillbirths among women exposed to duloxetine during pregnancy. For minor malformations, there was some tendency for an increased risk, but estimates had wide CIs and the tendency decreased when duloxetine exposed were compared with venlafaxine exposed or duloxetine discontinuers, as well as in adjusted and PS-matched analyses. Confounding by indication or other unmeasured confounding may explain the risk.

Interpretation

The results of the present study are in line with previous studies [31,32] and case reports [26,52,53] finding no increased risk for malformations associated with duloxetine exposure. A review from 2015 concluded that there was insufficient data on duloxetine to draw definitive conclusions about its safety in pregnancy [54]. A review from 2016 concluded that women exposed to duloxetine during the first trimester (n = 668) had no increased risk of congenital malformations (OR 0.80, 95% CI 0.46 to 1.29) [33]. The present study corroborates these findings based on a considerably larger group of duloxetine-exposed women (n = 1,512) while addressing more potential confounding factors and including PS-matched analyses and sensitivity analyses. Huybrechts and colleagues [32] did a recent study in the US and found no increased risk for malformation overall, but a small increased risk of cardiac malformation. Although no increased risk of cardiac malformations was found in the present study, it must be noted that there was an increased risk of “other anomalies and syndromes” (See Table B in S1 Tables for the full list of other anomalies and syndromes, but it includes, e.g., craniosynostosis, situs inversus, and fetal alcohol syndrome). This must be interpreted with caution based on the low number of cases (n = 14) and the wide CIs. Since we find no clear pharmacological mechanism explaining the association, the result is interpreted to be a chance finding.

A small Swedish study from 2007 investigating SNRI/NRIs (not including duloxetine) found no increased risk for stillbirth when compared to the background population or to women exposed to SSRI during pregnancy [55]. The present study, with a bigger population and more recent data, supports this finding.

Strengths and limitations

Due to the nationwide coverage, high validity, and completeness of the included registers, the risk of selection (sampling, allocation, and lost to follow-up) bias was minimal. There was no risk of recall bias. The quality of malformation diagnoses was validated in Danish data and was found to have a predictive value of 88%, with a completeness of 90% [56]. Diagnoses of heart defects were found to have a positive predictive value of 98.4% [57]. For the present study, differential misclassification depending on exposure status was not suspected. Information on malformation among abortions and stillbirths was not available. This can lead to an underestimation of the risk if duloxetine exposure is associated with malformations leading to these outcomes. Information on LMP was precise as it was based on the mother’s self-report and 2 subsequent ultrasounds in the first and second trimester.

The primary exposure definition was the redemption of a single prescription. Although the medication has been prescribed, dispensed, redeemed, and paid for, there is a probability that the patient did not ingest the drug. Sensitivity analyses were performed with a stricter definition of exposure (>1 redeemed prescription) under the assumption that redeeming multiple prescriptions increases the likelihood that the medication was taken. These sensitivity analyses did not change the overall results. Information on drug exposure during hospitalization was unavailable. This might have led to misclassification of exposure as exposure is based on redeemed prescriptions from community pharmacies. However, we assume that women hospitalized because of depression also redeem prescriptions of antidepression medication. Also, it is expected that most women with the indication for antidepressants are treated outside the hospital since only 1.6% of the total duloxetine use in the time period was administrated in hospitals in Denmark [58]. Important unavailable potential confounders were alcohol, illicit drug use, and poor adherence to folic acid supplementation during pregnancy [59]. Women with depressive disorder are more likely to smoke, use alcohol or other substances, and, in general, not to adhere to recommended health behavior during pregnancy. This may confound the association between duloxetine and pregnancy outcomes and increased risk of malformations may erroneously be attributed to duloxetine [60,61]. Socioeconomic status (education and income) and smoking were included as covariates. Due to the concern of unmeasured confoundings (e.g., alcohol and illicit drug use) and confounding by indication, SSRI-exposed and venlafaxine-exposed women were used as comparators as they are expected to have similar health behavior as duloxetine-exposed women.

Indication for duloxetine was not available as a recorded covariate. In addition to depression, duloxetine is indicated for the treatment of neuropathy, anxiety, severe stress reaction, and stress urinary incontinence. In the analyzed cohort of pregnant women, the prevalence of these indications is, however, expected to be very low. Depression severity, which might also lead to confounding, and a direct measurement for depression severity was unavailable. This potential confounding was addressed by including diagnoses of neuropathy, anxiety, severe stress reaction, and stress urinary incontinence as covariates, as well as covariates that describe depression severity (depression diagnosis recorded at hospital contact, psychiatric hospitalization, and outpatient visits).

In the analyses of major malformation subtypes and stillbirth, adjusted analyses could not be consistently performed due to the low number of outcome events despite the cohort including more than 2 million births. As opposed to adjusted analyses, the PS-matched analyses were possible despite few outcome events.

The study included all registered pregnancies resulting in a birth (live or stillbirth). We believe that the results have a high external validity especially applicable to other western European countries with free and universal healthcare, where treatment regimens and population characteristics are comparable, as well as to the US, where indications and treatment guidelines are similar to the studied population. Despite the large cohort, the number of women exposed to duloxetine during pregnancy was limited, and future studies should focus on analyzing larger cohorts and additional safety outcomes (e.g., preterm birth, abortions, and SGA). Improved measurements of exposure, outcome, and covariates could also yield more precise estimates. In addition, information on duloxetine indication and depression severity could add relevant information.

Conclusions

Based on this observational register-based nationwide study with data from Sweden and Denmark, no increased risk of major and minor congenital malformations or stillbirths was associated with exposure to duloxetine during pregnancy.

STROBE Statement—Checklist of items that should be included in reports of cohort studies.

(PDF)

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Observational study to assess maternal and fetal outcomes following exposure to duloxetine: Denmark and Sweden National Pregnancy Registry Study.

(PDF)

Click here for additional data file.

Table A. Minor malformation ICD-10 codes. Table B. ICD-10 codes for major malformation subtypes. Table C. ICD-10, ATC codes, and time periods for comorbidity. Table D. ATC codes for comedication. Table E. Covariates in the models of the primary analyses (the figures shown in the manuscript). Table F. Baseline table for all covariates, major and minor malformation analyses. Before and after propensity score matching. Table G. Baseline table for all covariates, stillbirth analyses. Before and after propensity score matching. Table H. Number of events per thousand pregnancies (95% Wald confidence intervals). Table I. Major malformation, sensitivity analyses. Table J. Minor malformation, sensitivity analyses. Table K. Malformation subtype: Heart defect. Table L. Malformation subtype: Digestive system. Table M. Malformation subtype: Ear, face, and neck. Table N. Malformation subtype: Eye. Table O. Malformation subtype: Genitals. Table P. Malformation subtype: Abdominal wall. Table Q. Malformation subtype: Limb. Table R. Malformation subtype: Nervous system. Table S. Malformation subtype: Orofacial clefts. Table T. Malformation subtype: Respiratory. Table U. Malformation subtype: Urinary tract. Table V. Malformation subtype: Other anomalies/syndromes. Table W. Stillbirth, sensitivity analyses.

(DOCX)

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30 Sep 2020

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3 Feb 2021

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Requests from the editors:

Comments from the reviewers:

Reviewer #1: "Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth A nation-wide cohort study in Denmark and Sweden" seeks to investigate the possible effect of Duloxetine (prescribed as an antidepression etc.) exposure, on (major/minor) congenital infant malformation and stillbirth. The study was conducted on a cohort of all pregnancies in Sweden and Denmark, from 2004-2016. The major finding was that duloxetine exposure did not result in increased risk of malformation/stillbirth, from adjusted and propensity score-matched (cohort details in Table S6A/B) logistic regression analyses.

Concerns may remain over the relatively low number of Duloxetine events (60+ for major/minor malformation, 5 stillbirths), which would seem to make drawing definitive conclusions difficult. However, given the national-level scope of the study and lack of prior large cohort studies, this would appear to be a valuable addition to the literature. Nevertheless, some issues might be addressed:

1. For the cohort selection flowchart from Figure 1, there appears to possibly be an inconsistency. It is presented that both malformation & stillbirth cohorts begin with the same initial cohort (N=2,193,732), and that the malformation cohort has N=1,042 subjects who "redeemed prescription of duloxetine 3 months prior to LMP and not during exposure period".

However, given that the only prior exclusion criteria for the stillbirth cohort was "mother migrated 3 months prior to LMP until delivery", and that this appears a strict subset of "mother migrated 12 months prior to LMP until 12 months past delivery" for the malformation cohort (amongst other exclusion criteria for the malformation cohort), it would appear that the corresponding number of subjects excluded for "redeemed prescription of duloxetine 3 months prior to LMP and not during exposure period" for the stillbirth cohort should be not less than that for the malformation cohort (whereas it is presented as N=975). The authors might clarify if this reasoning is correct or flawed.

2. On Page 8, it is mentioned that "When fitting each model, covariates were removed, if the model could not be estimated" for adjusted/PS models. The authors might consider explaining in greater detail why certain covariates would cause a model not to be able to be estimated, and what models were affected/covariates were removed for these affected models. Details on excluded covariates might be added to Supplementary Figures S1 to S12 as appropriate.

3. On Page 9, it is mentioned that missing income would be imputed from one year prior and then one year after LMP if possible, and 1 year prior for education. Does this cover all missing data cases, and if not, what was the final imputed value for cases where no income/education/etc. data was available at all?

4. On Page 9, it is noted that four sensitivity analyses were performed. However, their charts/details were not located, despite patterns on the results of these four sensitivity analyses being referenced in the text discussion. In particular, for BMI, the main analyses in Figures 2 to 4 do not appear to mention BMI in their marker descriptions, while subanalyses from Figure S2 onwards mention BMI (grouped) in marker 3, which however does not appear to have been applied (also covered as a minor issue). The authors might consider including the details of these sensitivity analyses.

5. On Page 14, it is stated that "...adjusted analyses could not consistently be performed due to the low number of outcome events despite of the cohort including more than 2 million births. The PS matched analyses performed better with few outcome events."; it might be clarified as to what "better" in the second sentence means - better in some statistical sense, or better by the results?

Minor issues:

6. On Page 8, the relevant literature contributing to covariate selection might be referenced if possible.

7. The motivation for using SSRI-exposed and Venlafaxine exposed patients as comparators might be moved from the discussion (Page 13), to the initial description of the methodology.

8. From Figure 1, it might be clarified whether the N=73 stillbirths (abortions after week 22) were spontaneous or intentional.

9. Still on the malformation subtype analyses as presented in Supplementary Figures S1 to S12, certain values are presented as <5 (e.g. in S3, S5, S6, etc.); Might the exact number of events be presented & analyzed instead?

10. For Supplementary Figure S6, unconventional OR (i.e. 416E3, 174E3) are provided, which might indicate a technical issue (e.g. division by zero) in computation of the values. This might be addressed.

11. For Supplementary Figures S2 to S12, while details for Markers 1, 2 and 3 are provided for each figure, it appears that only "1,2" is ever labelled for the PS-matched row for each comparator. If so, the authors might consider simply describing the propensity score criteria for PS-matched without requiring a Marker column.

12. There may be some grammatical/spelling issues, e.g. "the reproductive age"; "data collected form registers", "statistical significant findings" in the Abstract, "this tendency were reduced" (Page 10), etc. These might be addressed.

Reviewer #2: This is a study from Sweden and Denmark aiming to explore whether use of duloxetine in pregnancy could increase the risk of major and minor congenital malformation, and the risk of stillbirth. The authors linked data from nationwide registers from Sweden and Denmark covering all registered births from 2004-2016. Generally, this is an important research question although several previous studies have shown that use of duolexitine in pregnancy did not increase the risk of malformations and stillbirths, and thus the novelty of the study in the field is relatively limited. Also, some methodological aspects of the paper should be better addressed by the authors for a better interpretation of the findings. Here below are more specific comments on the various sections of the paper.

ABSTRACT:

in the "Exposure" paragraph you wrote "4) women discontinuing duloxetine treatment before pregnancy." Maybe you wanted to write during pregnancy?

INTRODUCTION:

You should review the English especially in the second paragraph.

METHODS:

In the "Cohorts" paragraph you did not specify inclusion/esclusion criteria on age at delivery and gestational age. I recommend to you to consider such inclusion/exclusion criterias: ages at delivery between 12-55 years and gestational age between 22-42/46 gestational weeks. This latter, especially, is very important following the stillbirth outcome that you chose to evaluate.

"Exposure, comparison groups and outcome" paragraph:

(i) In the second paragraph I reccomad to specify the fourth comparison group as follow: "4) duloxetine discontinues: at least one redeemed prescription of duloxetine between 365 day priorLMP to LMP, BUT NOT DURING PREGNANCY, if it is the case.

(ii) you stated that you excluded women with duloxetine exposure from 90 days prior to LMP, but no exposure from LMP to 90 days after LMP, why you made this choice if in the sensitivity analysis you evaluated the overlap days of supply?

(ii) in the last sentence you define the stilbirth as a no signs of life at birth after week 22 of pregnancy, once again it is very important that all women included in the cohort have at least 22 weeks of gestation.

"Statistical methods":

(i) in the third paragraph you said that "when fitting each model, covariates were removed, if the model could not be estimated.". Since you consider rare outcomes I recommend you to did not performe multivariate analysis but adjusted for the propensity score. I sow that you delete a huge number of women after the PS matching, why did you not performe the propensity score stratification? I would delete the multivariate analysis.

(ii) you said that you assess the comorbidity in the 5 years prior to LMP, are you sure that all women have this follow-up prior to LMP? In case yes, you should add as inclusion/exclusion criteria.

(iii) when you present the four sensitivity analysis you performed, I would say that you performed them to evaluate the effect of potential misclassification of exposure.

(iv) in the third sensitivity analysis you stated that you restricted the cohort to the first pregnancy within the study, why did you not use the generalized estimating equation to account for potential correlation within women with multiple pregnancies during the considered period in the unadjusted analyses? You should assess in the undjusted analysis if the estimate with and without the generalized estimating equation to account for potential correlation within women with multiple pregnancies during the considered period are different, In case not you can delete the third sensitivity analysis.

(v) you performed the last sensitivity analysis in complete case sample with BMI information, can you consider the missing for that variable as missing at random?

RESULTS:

You shoal review the English and make all the paragraph more descriptive.

TABLE and FIGURE:

(i) I would collapse the figure 2 and figure 3 in 1 Figure with Panel A and Panel B. You would have only the unadjusted and PS-matched (or I recommend to you to try the PS stratification) estimate for each comparison.

(ii) I suggest to move the Table 2 in the supplementary materials

(iii) Table S6 I would take only the Post STD diff.

Reviewer #3: This is a well-written revised manuscript that describes a study examining whether duloxetine exposure in pregnancy is associated with malformations or stillbirths. The study is well designed and controls for confounding by indication in several different ways which extremely important for this type of study. I have no suggestions for changes. Well done!!!

Any attachments provided with reviews can be seen via the following link:

[LINK]

11 Mar 2021

Submitted filename: Ankarfeldt_Duloxetine_RebuttalLetter.docx

Click here for additional data file.

24 Aug 2021

Dear Dr. Ankarfeldt,

Thank you very much for submitting your manuscript "Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth: A nation-wide cohort study in Denmark and Sweden" (PMEDICINE-D-20-04640R2) for consideration at PLOS Medicine.

Your paper was evaluated by a senior editor and discussed among all the editors here. It was also discussed with an academic editor with relevant expertise, and sent to two of the original reviewers, including a statistical reviewer. The reviews are appended at the bottom of this email and any accompanying reviewer attachments can be seen via the link below:

[LINK]

Although we will not be able to accept the manuscript for publication in the journal in its current form, we would like to consider a revised version that addresses the reviewers' and editors' comments. Obviously we cannot make any decision about publication until we have seen the revised manuscript and your response.

In revising the manuscript for further consideration, your revisions should address the specific points made by the reviewers and editors. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments, the changes you have made in the manuscript, and include either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please submit a clean version of the paper as the main article file; a version with changes marked should be uploaded as a marked up manuscript.

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We expect to receive your revised manuscript by Sep 14 2021 11:59PM. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

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Please use the following link to submit the revised manuscript:

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Your article can be found in the "Submissions Needing Revision" folder.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

We look forward to receiving your revised manuscript.

Sincerely,

Caitlin Moyer, PhD

Associate Editor

PLOS Medicine

plosmedicine.org

-----------------------------------------------------------

Requests from the editors:

1. Reviewer 2 Comment: Please do address the remaining comments of Reviewer 2. The editors feel that it is acceptable to present both multivariable and propensity-score matched analyses. Please do address the Reviewer’s request regarding restricting the analysis to those with at least 1 year of prior registry data. If this is not feasible we request that you include a thorough discussion of the limitation related to identifying a confounder in those with 5 years of back follow up in registry vs those with fewer years available in registry.

2. Data availability statement: For data that are freely or publicly available, please note this and provide more specific/direct links to access the Statistics Denmark and Statistics Sweden, and Swedish National Board of Health and Welfare data used in this study. For more information, please see the policy at

http://journals.plos.org/plosmedicine/s/data-availability

and FAQs at

http://journals.plos.org/plosmedicine/s/data-availability#loc-faqs-for-data-policy

3. Throughout text: Please include line numbers with the revised version.

4. Throughout text: Please use square brackets for in-text references, placed before the sentence punctuation. For multiple references within brackets, please do not include spaces.

5. Abstract: Please structure your abstract using the PLOS Medicine headings (Background, Methods and Findings, Conclusions).

6. Abstract: Please fully define all abbreviations at first use in the text (SNRI, SSRI, etc).

7. Abstract: Methods and Findings: In this section, please clearly describe the study design, population and setting, number of participants, years during which the study took place, length of follow up, and main outcome measures. Please quantify the main results (with 95% CIs and p values). Please note the important dependent variables that are adjusted for in the analyses. In the last sentence of the Abstract Methods and Findings section, please describe the main limitation(s) of the study's methodology.

8. Abstract: Conclusion: We suggest revising to “...no increased risk of major or minor congenital malformations or stillbirth was associated with exposure to duloxetine during pregnancy.”

9. Author summary: At this stage, we ask that you include a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract. Please see our author guidelines for more information: https://journals.plos.org/plosmedicine/s/revising-your-manuscript#loc-author-summary

10. Introduction: The final paragraph of the section “The present study is based on a safety study…” seems more appropriate for the Methods section.

11. Methods: Please provide more description of the Prescription, Patient, and Medical Birth registers used in the study.

12. Methods: Where the four non-exposed groups are described, it might be helpful to mention that venlafaxine is another SNRI.

13. Methods: From Figure 3 and Table S8 it seems that adjusted analyses for the stillbirth outcome were not done. Please clarify this in the text, similar to: “For analyses of malformation subtypes with less than outcome events in the exposed group, only unadjusted and PS-matched analyses were performed.”

14. Methods: Did your study have a prospective protocol or analysis plan? Please state this (either way) early in the Methods section.

a) If a prospective analysis plan (from your funding proposal, IRB or other ethics committee submission, study protocol, or other planning document written before analyzing the data) was used in designing the study, please include the relevant prospectively written document with your revised manuscript as a Supporting Information file to be published alongside your study, and cite it in the Methods section. A legend for this file should be included at the end of your manuscript.

b) If no such document exists, please make sure that the Methods section transparently describes when analyses were planned, and when/why any data-driven changes to analyses took place.

c) In either case, changes in the analysis-- including those made in response to peer review comments-- should be identified as such in the Methods section of the paper, with rationale.

15. Methods: Please ensure that the study is reported according to the STROBE guideline, and include the completed STROBE checklist as Supporting Information. Please add the following statement, or similar, to the Methods: "This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (S1 Checklist)."

The STROBE guideline can be found here: http://www.equator-network.org/reporting-guidelines/strobe/

When completing the checklist, please use section and paragraph numbers, rather than page numbers.

16. Results: Please move the baseline table for stillbirth analyses to the main text.

17. Results: For all analyses described, please present the complete main results together with 95% CIs and p values. For example, please present the results for this analysis, with 95% CIs and p values. “For minor malformations, the unadjusted analysis of duloxetine exposed compared with duloxetine nonexposed showed an increased risk. However, in the adjusted and PS-matched analyses the risk was lower and showed no statistically significant increase.”

18. Results: Rather than describing “Similar patterns were observed in the sensitivity analyses.” for the stillbirth and minor malformations analyses, please describe what was observed.

19. Results: “It is of note that a statistically significant increased risk of “other anomalies and syndromes” was found when duloxetine exposed women were compared with SSRI exposed. The PS-matched analyses yielded OR 2.43 (95% CI 1.10-5.38).” Please make it more clear that the PS-matched result presented here is for the SSRI-exposed comparison.

20. Discussion: Please present and organize the Discussion as follows: a short, clear summary of the article's findings; what the study adds to existing research and where and why the results may differ from previous research; strengths and limitations of the study; implications and next steps for research, clinical practice, and/or public policy; one-paragraph conclusion.

21. Discussion: Please clarify whether this refers to increased risk of malformation or stillbirth: “Like the present study, a small Swedish study analyzing the association between SNRI/NRIs (not including duloxetine) and stillbirth found no increased risk.”

22. Discussion: We suggest replacing “compliance” with “adherence” when referring to recommended folic acid supplementation.

23. Discussion: Generalizability: In this paragraph, we suggest a broader discussion on clinical or policy implications and further directions based on the findings reported here.

24. Disclosure of conflicts of interest: These can be removed from the main text of the manuscript, and please make sure all information is completely and accurately entered in to the manuscript submission metadata.

25. References: Please use the "Vancouver" style for reference formatting, and see our website for other reference guidelines https://journals.plos.org/plosmedicine/s/submission-guidelines#loc-references

26. Reference List: Reference 49: Papers cannot be listed in the reference list until they have been accepted for publication or are publicly available on a preprint archive. The information may be cited in the text as a personal communication with the author if the author provides written permission to be named. Alternatively please provide a different appropriate reference.

27. Reference 51: Please provide the complete citation information.

28. Figure 1: Please define all abbreviations in the legend (SSRI, LMP).

29. Figure 2 and Figure 3: Please define all abbreviations in the legend (SSRI).

30. Table S5: Please move the table to the main section of the paper.

31. All tables: Please make sure to define all abbreviations used in the tables in the legends.

Comments from the reviewers:

Reviewer #1: We thank the authors for addressing the previous issues raised, and have no further concerns.

Reviewer #2: Dear Editor and Authors,

my comment is regarding only the statistical methodology. I think that it has no sense to perform both the multivariate and ps matching adjustment, especially in this case where the prevalence of the outcomes are very rare.

The PS's methodology is, in fact, a methodology used to (i) avoid the overfitting problem (you should record at least 8 events for each confounder included in the model), and (ii) compare exposed and unexposed comparable.

Moreover, you should consider that if you do not require that all women have at least 5 years back-follow up available, the probability to find a confounder in women with 5 years vs those with fewer years is different. Since you considered chronic conditions and you assessed the concomitant medications only in the year before LMP I will recommend you to ask as inclusion criteria that all women have at least one year prior to the LMP and to evaluate the confounders in this time window.

Any attachments provided with reviews can be seen via the following link:

[LINK]

13 Sep 2021

Submitted filename: Ankarfeldt_Duloxetine_rebuttal_letter.docx

Click here for additional data file.

4 Oct 2021

Dear Dr. Ankarfeldt,

Thank you very much for re-submitting your manuscript "Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth

A nation-wide cohort study in Denmark and Sweden" (PMEDICINE-D-20-04640R3) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor. I am pleased to say that provided the remaining editorial and production issues are dealt with we are planning to accept the paper for publication in the journal.

The remaining issues that need to be addressed are listed at the end of this email. Any accompanying reviewer attachments can be seen via the link below. Please take these into account before resubmitting your manuscript:

[LINK]

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

In revising the manuscript for further consideration here, please ensure you address the specific points made by the editors. In your rebuttal letter you should indicate your response to the editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. If you haven't already, we ask that you provide a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract.

We expect to receive your revised manuscript within 1 week. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.

We look forward to receiving the revised manuscript by Oct 11 2021 11:59PM.

Sincerely,

Caitlin Moyer, Ph.D.

Associate Editor

PLOS Medicine

plosmedicine.org

------------------------------------------------------------

Requests from Editors:

1. Title: Please format the title as: “Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth: A nation-wide cohort study in Denmark and Sweden”

2. Data availability statement: Please note that the link provided for the Swedish National Board of Health and Welfare data did not work, and there may be a typo in the link. If accurate please replace with: https://www.socialstyrelsen.se/en/statistics-and-data/statistics/statistical-databases/

We suggest revising slightly to: “Data from the Danish and Swedish registers are third party data, meaning that we as researchers do not hold the data, but have obtained data after application at relevant parties. The Danish data can be applied for at Statistics Denmark (https://www.dst.dk/en/TilSalg/Forskningsservice). The Swedish data

can be applied for at Statistic Sweden (https://www.scb.se/en/About-us/contact-us/) and Swedish National Board of Health and Welfare data (https://www.socialstyrelsen.se/en/statistics-and-data/statistics/statistical-databases/).

3. Abstract: Methods and Findings: Line 45: We suggest revising to “A population-based observational study was conducted based on data from registers in Sweden and Denmark.” or similar, to make this a complete sentence.

4. Abstract: Methods and Findings: Line 59-62: Please revise this sentence to: “Duloxetine exposed vs duloxetine non-exposed propensity score matched analyses showed odds ratios (OR) of 0.98 (95% confidence interval [CI] 0.74-1.30) for major malformations, 1.09 (95% CI 0.82-1.45) for minor malformation, and 1.18 (95% CI 0.43-3.19) for stillbirths.” or similar to clarify. Please also include p values in addition to reporting the OR and confidence intervals.

5. Abstract: Methods and Findings: Line 63-65: Please clarify this sentence, such as: “The main limitations for the study were that the indication for duloxetine and a direct measurement of depression severity were not available to include as covariates.” if this is what was meant.

6. Author summary: Why was this study done? We suggest combining the first two points, such as: “Many women of reproductive age take drugs used to treat depression, including duloxetine, a selective serotonin-norepinephrine reuptake inhibitor (SNRI) approved in 2004 for the treatment of depression, and the use of which has been increasing.” or similar.

7. Author summary: What did the researchers do and find? We suggest combining the second and third bullet points: “From more than 2 million births identified, information on drug exposure, comorbidities, education and income, and congenital malformations and stillbirths was gathered.” or similar.

8. Author summary: What did the researchers do and find? We suggest revising the third bullet point to: “The analyses taking into account factors beyond duloxetine exposure did not reveal associations between exposure to duloxetine during pregnancy and risk for malformations or stillbirth.” or similar.

9. Methods: Study protocol: Thank you for including the link to the protocol on the ENCePP website. We request that you include a copy of the protocol as a supporting information file. Please remove confidential information or confidentiality statements and any trademark/copyright symbols. Also, please clarify that the online protocol also seems to suggest that preterm birth and small for gestational age would be included in the analyses, and describe when and the rationale for the change in protocol.

10. Methods: Line 227: We suggest renaming the STROBE checklist file to "S1 Checklist" or similar.

11. Methods: Line 228: We suggest revising to “The prospectively developed protocol was followed…” if this is accurate. At line 232 please revise to “...comedication should have been identified one year prior to LMP, but was changed to comedication during the relevant exposure time window…” if accurate.

12. Results: Line 245-247,Lines 254-257, Lines 262-264, Lines 266-267, and Lines 269-272: Please also present the p values for the PS-matched results in the text.

13. Discussion: Line 291-294: It may be helpful to briefly mention some of the “other anomalies and syndromes” that would fall into this category.

14. Discussion: Line 295-296: We suggest providing some additional context for this previously published study investigating stillbirth risk, and expanding to discuss your findings and interpretations in light of this.

15. Discussion: Line 340: Please revise to “...the number of women exposed to duloxetine during pregnancy was limited…” if this is accurate.

16. Line 360-365: Please remove the data availability statement from the main text, and please ensure that the data availability statement of the manuscript submission is complete and accurate.

17. References: Please use the "Vancouver" style for reference formatting, and see our website for other reference guidelines https://journals.plos.org/plosmedicine/s/submission-guidelines#loc-references

For example, in reference 3 the journal title should be abbreviated as “Obstet Gynecol” and it seems as if “[Article]” could be removed from reference 54. In addition, the link provided for reference 46 does not seem to work. Please check each individual reference for accuracy, journal title abbreviations and all formatting throughout.

18. Figure 2 and Figure 3, Table 1 and Table 2: In the legends, please correct “LPM” to “LMP” if this is accurate.

19. Figure 2 and 3 Legends: Please note that the legends on page 21 refer to covariate information presented in Table S6, while this information appears to be presented in Table S5.

20. Supporting information file: In the “Contents” it seems as if Table S8 listed as being on page 17 is a typo and should be Table S6. Also please note that there are two versions of Tables S6 and S7 included.

21. Supporting information Table S6 and S7. Please change the reference to the list of covariates in the legends to Table S5 rather than Table S6.

Any attachments provided with reviews can be seen via the following link:

[LINK]

15 Oct 2021

Dear Dr Ankarfeldt,

On behalf of my colleagues and the Academic Editor, Jenny E Myers, I am pleased to inform you that we have agreed to publish your manuscript "Exposure to duloxetine during pregnancy and risk of congenital malformations and stillbirth: A nation-wide cohort study in Denmark and Sweden" (PMEDICINE-D-20-04640R4) in PLOS Medicine.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. Please be aware that it may take several days for you to receive this email; during this time no action is required by you. Once you have received these formatting requests, please note that your manuscript will not be scheduled for publication until you have made the required changes.

In the meantime, please log into Editorial Manager at http://www.editorialmanager.com/pmedicine/, click the "Update My Information" link at the top of the page, and update your user information to ensure an efficient production process.

Please also address the following editorial requests:

1. Abstract: Line 50: Please remove "sex" from the abstract as this does not appear to have been included as a confounder variable.

2. Discussion: Line 326: Please change "comply with" to "adhere to" in this sentence.

3. Supporting Information File: Please remove the box with "Confidential Information" from page 1 of the Protocol document included with the supporting information.

PRESS

We frequently collaborate with press offices. If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximise its impact. If the press office is planning to promote your findings, we would be grateful if they could coordinate with medicinepress@plos.org. If you have not yet opted out of the early version process, we ask that you notify us immediately of any press plans so that we may do so on your behalf.

We also ask that you take this opportunity to read our Embargo Policy regarding the discussion, promotion and media coverage of work that is yet to be published by PLOS. As your manuscript is not yet published, it is bound by the conditions of our Embargo Policy. Please be aware that this policy is in place both to ensure that any press coverage of your article is fully substantiated and to provide a direct link between such coverage and the published work. For full details of our Embargo Policy, please visit http://www.plos.org/about/media-inquiries/embargo-policy/.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Thank you again for submitting to PLOS Medicine. We look forward to publishing your paper.

Sincerely,

Caitlin Moyer, Ph.D.

Associate Editor

PLOS Medicine