Risk of miscarriage in women with chronic diseases in Norway: A registry linkage study.

BACKGROUND: Increased risk of miscarriage has been reported for women with specific chronic health conditions. A broader investigation of chronic diseases and miscarriage risk may uncover patterns across categories of illness. The objective of this study was to study the risk of miscarriage according to various preexisting chronic diseases. METHODS AND
FINDINGS: We conducted a registry-based study. Registered pregnancies (n = 593,009) in Norway between 2010 and 2016 were identified through 3 national health registries (birth register, general practitioner data, and patient registries). Six broad categories of illness were identified, comprising 25 chronic diseases defined by diagnostic codes used in general practitioner and patient registries. We required that the diseases were diagnosed before the pregnancy of interest. Miscarriage risk according to underlying chronic diseases was estimated as odds ratios (ORs) using generalized estimating equations adjusting for woman's age. The mean age of women at the start of pregnancy was 29.7 years (SD 5.6 years). We observed an increased risk of miscarriage among women with cardiometabolic diseases (OR 1.25, 95% CI 1.20 to 1.31; p-value <0.001). Within this category, risks were elevated for all conditions: atherosclerosis (2.22; 1.42 to 3.49; p-value <0.001), hypertensive disorders (1.19; 1.13 to 1.26; p-value <0.001), and type 2 diabetes (1.38; 1.26 to 1.51; p-value <0.001). Among other categories of disease, risks were elevated for hypoparathyroidism (2.58; 1.35 to 4.92; p-value 0.004), Cushing syndrome (1.97; 1.06 to 3.65; p-value 0.03), Crohn's disease (OR 1.31; 95% CI: 1.18 to 1.45; p-value 0.001), and endometriosis (1.22; 1.15 to 1.29; p-value <0.001). Findings were largely unchanged after mutual adjustment. Limitations of this study include our inability to adjust for measures of socioeconomic position or lifestyle characteristics, in addition to the rareness of some of the conditions providing limited power.
CONCLUSIONS: In this registry study, we found that, although risk of miscarriage was largely unaffected by maternal chronic diseases, risk of miscarriage was associated with conditions related to cardiometabolic health. This finding is consistent with emerging evidence linking cardiovascular risk factors to pregnancy complications.

Introduction

Miscarriage occurs in 12% to 15% of recognized pregnancies [1-4]. Although the underlying cause of most miscarriages is unknown, they presumably result from a complex interplay between parental age, genetic, hormonal, metabolic, immunological, and environmental factors [5,6]. Genetic factors, including parental chromosomal rearrangements and abnormal embryonic genotypes or karyotypes, are found in more than half of recurrent miscarriages [6].

Various studies of specific illnesses have suggested an association with risk of miscarriage. These include systemic lupus erythematosus [7], type 1 diabetes [8,9], celiac disease [10,11], asthma/allergies [12], thyroid disorders [13-16], Addison disease [17,18], type 2 diabetes [9,19,20], parathyroid disorders [21,22], Cushing syndrome [23], migraine [24], and epilepsy [25,26]. These scattered findings suggest that immunological, metabolic, or endocrinological mechanisms might be linked to miscarriage risk, any of which is biologically plausible since all play a role in development and function of the placenta [27-30]. However, most of these studies were based on relatively small samples, and most are retrospective and therefore susceptible to recall bias.

The Norwegian health registries contain comprehensive registration of all recognized pregnancies resulting in contact with healthcare services. Our objective was to study the risk of miscarriage in relation to women’s chronic illness present prior to pregnancy. We examined the risk of miscarriage across a broad range of illnesses, including autoimmune, cardiometabolic, endocrinological, neurological, allergic, and reproductive.

Methods

This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) and REporting of studies Conducted using Observational Routinely-collected Data (RECORD) guidelines (S1 RECORD Checklist). The study was conducted according to a prespecified analysis plan (S1 Analysis Plan). The only deviation from this plan was that we not only evaluated the risk of miscarriage according to the individual chronic diseases but also according to subgroups which might share underlying disease pathways.

Study population and data sources

We conducted a registry-based study using Norwegian national registries. The study population consisted of all registered pregnancies in Norway with an estimated date of conception between January 1, 2010 and December 31, 2016. Information on pregnancies came from 3 national health registries: the Medical Birth Registry of Norway, the Norwegian Patient Registry, and the general practitioner database. Hospital discharges in the patient registry are coded according to International Classification of Diseases (ICD) version 10, while the general practitioner database is coded according to the International Classification of Primary Care (ICPC-2) [31]. The birth registry includes information on all pregnancies ending at 12 gestational weeks or later (live births, stillbirths, late miscarriages, and late induced abortions). Miscarriages before 12 weeks were captured by registrations in the patient registry (with information on all contact with specialist healthcare services) and by the general practitioner database (with information on all contact with primary healthcare services). We used information from the patient registry to account for induced abortions. Ectopic pregnancies were excluded from the study. We linked information from the 3 health registries by using the unique personal identification numbers given to all Norwegian citizens. A description of the data sources and linkage procedures is provided in the Supplement Methods (S1 Text). The analysis was based on de-identified data. The study was approved and participant consent was waived by the Regional Committee for Medical and Health Research Ethics South-East, reference number 2014/404.

Pregnancy outcomes and identification of unique pregnancies

We identified live births and fetal deaths after 12 gestational weeks through the birth registry. We defined stillbirth as a fetal death at 20 gestational weeks or later, or death of a fetus with a birthweight of 500 grams or more. Miscarriage were defined as fetal deaths before 20 gestational weeks where the fetus also had a birthweight less than 500 grams. In addition, we used the patient registry to capture miscarriages before 12 completed gestational weeks using the following ICD-10 codes: hydatidiform mole (O01); blighted ovum and nonhydatidiform mole (O02.0); missed abortion (O02.1); other specified abnormal products of conception (O02.8); abnormal product of conception, unspecified (O02.9); spontaneous abortion (O03); and threatened abortion (O20.0). These are the diagnostic codes we previously used to identify miscarriages in the patient registry [32]. The following ICD-10 codes were used to define induced abortions in the patient registry: medical abortion (O04), other abortion (O05), and unspecified abortion (O06).

The present study expands our earlier definition of miscarriage by including events reported in the general practitioner database [32]. Registrations of bleeding in pregnancy (ICPC-2 code W03) or spontaneous abortion (ICPC-2 code W82) in the general practitioner database were included as miscarriages if there was no subsequent registration of delivery or birth.

Pregnancies in the patient and general practitioner databases are not registered with unique pregnancy IDs, which means that follow-up visits for the same miscarriage produce multiple registrations. We took the following steps to define unique pregnancies. First, we required a minimum of 6 weeks (42 days) between 2 successive records of miscarriage in the patient registry, and a minimum of 3 months (90 days) between 2 successive records of miscarriage in the general practitioner database, to consider them distinct pregnancies. These cutoffs were chosen by inspecting the distribution of the time between registrations in the 2 registers. We used a longer time interval between the registrations in the general practitioner database, because women may have more and longer duration of follow-up visits with their general practitioners after a miscarriage. The routine postpartum checkup is done in general practice 6 weeks after delivery, and we required at least additional 6 weeks for the next registration to be defined as a new pregnancy. Second, we required that a record of a miscarriage or induced abortion in the patient or general practice databases be at least 6 weeks (patient registry) or 3 months (general practitioner database) after a registered delivery in the birth registry. Third, we excluded events registered as miscarriages or induced abortions that occurred within the gestational period of a registered pregnancy in the birth registry. For the 2 codes of threatened abortion (patient registry) and bleeding during pregnancy (general practitioner database), these were counted as miscarriages only if they did not have another code indicating the outcome of the pregnancy within 90 days.

Maternal chronic diseases

Diagnoses of chronic diseases were obtained from the patient and general practitioner databases. We included autoimmune diseases (autoimmune thyroiditis, systemic lupus erythematosus, type 1 diabetes, celiac disease, multiple sclerosis, rheumatoid arthritis/ankylosing spondylitis, ulcerative colitis, psoriasis, Addison disease, Crohn’s disease, haemolytic anemia), endocrinological diseases (Cushing syndrome, hypothyroidism, hyperthyroidism, hyperaldosteronism, hyperparathyroidism), cardiometabolic diseases (atherosclerosis, hypertensive disorders, type 2 diabetes), allergic diseases (asthma, allergic rhinitis, atopic dermatitis), neurological diseases (epilepsy, migraine), and reproductive diseases (polycystic ovary syndrome (PCOS) and endometriosis). We decided a priori what chronic diseases to include as exposures. The only notable changes based on what was decided a priori was the inclusion of an analysis of any cardiometabolic, any autoimmune, any reproductive, any endocrinological, any allergic, and any neurological diseases. In addition, autoimmune thyroiditis was included as part of review process. The various ICD-10 codes (specialist healthcare services) and ICPC-2 codes (primary healthcare services) used to capture the chronic disorders are listed in S1 Table. To reduce potential misclassification, we required 2 or more registrations of these diagnostic codes, with at least 1 registration prior to the pregnancy of interest. We estimated the duration of pregnancies in the birth registry by subtracting the estimated gestational age in days from the date of the birth. Since we did not have information on the gestational age of miscarriages or induced abortions identified in the patient and general practitioner databases, we required that a diagnosis of chronic diseases for these pregnancies be at least 12 weeks prior. Pregnancies with longer gestation than 12 weeks should be recorded in the birth registry.

Statistical analysis

We used generalized estimating equations with an exchangeable correlation structure to calculate the odds ratios (ORs) of miscarriage according to chronic conditions. We adjusted for the woman’s age at the start of pregnancy as a linear and squared term. We conducted additional multivariable analyses adjusting for the number of previous pregnancies. We also explored multivariable analyses with mutual adjustment for all underlying chronic diseases in the same model.

The risk of miscarriage is typically defined as the number of miscarriages divided by the sum of miscarriages and births. This definition does not take into account the competing risk of induced abortions. Pregnant women who intend to terminate their pregnancy are at risk of miscarriage up to the time of termination, but (by definition) there is no risk of birth. Miscarriages among these pregnancies contribute to the numerator of miscarriage risk with no corresponding contribution to the denominator, thus inflating the risk estimate for miscarriage. This bias can be adjusted by adding a portion of induced abortions to the denominator of miscarriage risk. We included 20% of induced abortions in the comparison group to account for the competing risk due to induced abortions. Details on the calculation of this adjustment value are provided in the Supplement Methods (S1 Text).

We explored stratified analyses by age (<35 years and 35 years and older) and by registration of the miscarriage in the specialist versus primary healthcare services. We also conducted a sensitivity analysis excluding molar pregnancies from the definition of miscarriage.

All analyses were conducted using STATA version 15 (Statacorp, Texas).

Patient and public involvement

No patients were involved in setting the research question or the outcome measures, nor were they involved in developing plans for recruitment, design, or implementation of the study. No patients were asked to advise on interpretation or writing up of results. There are no plans to disseminate the results of the research to study participants or the relevant patient community.

Results

We identified 593,009 pregnancies to 278,159 women with an estimated date of conception between January 1, 2010 and December 31, 2016 (Fig 1). Of these pregnancies, 409,952 (69.1%) ended in a live birth, 1,740 (0.3%) in stillbirth, 95,641 (16.1%) in induced abortion, while 85,676 (14.5%) in miscarriage. Miscarriage risk as a proportion of miscarriages plus live and stillbirths was 17.3%, reduced to 16.6% after adjusting for the competing risk of induced abortions. The mean age of women at the start of pregnancy was 29.7 years (SD 5.6 years). Fewer than 18% of women had a recorded chronic illness before pregnancy (Table 1), with the most common condition being allergic rhinitis (4%).

Fig 1

Illustration of identification of unique pregnancies across the birth, patient, and general practitioner databases.

Table 1

Prevalence of chronic diseases prior to pregnancy among 593,009 pregnancies in Norway between 2010 and 2016.

Group of diseases	Diseases	No. pregnancies to women with underlying chronic diseases (% out of all pregnancies)	No. pregnancies to women with chronic diseases ending in a miscarriage (% out of exposed pregnancies)
Autoimmune diseases	Type 1 diabetes	1,808 (0.30)	289 (18.6)
	Celiac disease	791 (0.13)	130 (18.8)
	Systemic lupus erythematosus	246 (0.04)	43 (20.2)
	Multiple sclerosis	720 (0.12)	162 (19.4)
	Rheumatoid arthritis/ Ankylosing spondylitis	2,559 (0.43)	418 (18.7)
	Ulcerative colitis	2,817 (0.48)	456 (18.3)
	Psoriasis	3,160 (0.53)	601 (17.4)
	Crohn’s disease	1,603 (0.27)	289 (21.0)
	Addison disease	56 (0.01)	11 (22.9)
	Haemolytic anemia	194 (0.03)	34 (21.1)
	Autoimmune thyroiditis	455 (0.08)	80 (20.9)
Cardiometabolic diseases	Type 2 diabetes	1,951 (0.33)	428 (25.1)
	Hypertensive disorders	5,334 (0.90)	1,085 (23.2)
	Atherosclerosis	66 (0.01)	21 (42.9)
Endocrinological diseases	Hypothyroidism	8,372 (1.41)	1,394 (18.6)
	Hyperthyroidism	2,374 (0.40)	378 (18.1)
	Hypoparathyroidism	29 (0.005)	9 (34.6)
	Hyperparathyroidism	128 (0.02)	22 (21.0)
	Cushing syndrome	31 (0.01)	10 (34.4)
Neurological diseases	Epilepsy	2,563 (0.43)	375 (17.8)
	Migraine	18,594 (3.14)	2,851 (17.7)
Allergic diseases	Asthma	16,294 (2.75)	2,405 (17.4)
	Allergic rhinitis	23,652 (3.99)	3,393 (16.2)
	Atopic dermatitis	7,674 (1.29)	1,020 (15.6)
Reproductive diseases	Polycystic ovary syndrome	83 (0.01)	20 (24.7)
	Endometriosis	4,827 (0.81)	1,011 (22.4)

After adjusting for women’s age, the category of illness with the strongest relation to miscarriage risk was cardiometabolic diseases (OR 1.25; 95% CI: 1.20, 1.31; p-value <0.001) (Fig 2). All 3 conditions in this category had substantial associations with miscarriage risk: atherosclerosis (OR 2.22; 95% CI: 1.42 to 3.49; p-value <0.001), type 2 diabetes (OR 1.38; 95% CI: 1.26 to 1.51; p-value <0.001), and hypertensive disorders (OR 1.19; 95% CI: 1.13 to 1.26; p-value <0.001). The category of reproductive diseases was the only other category with substantial risk (OR 1.22; 95% CI: 1.15, 1.29; p-value <0.001), although there were only 2 conditions in this category (endometriosis (OR 1.22; 95% CI: 1.15 to 1.29; p-value <0.001) and PCOS (OR 1.34; 95% CI: 0.87 to 2.08; p-value 0.2).

Fig 2

Adjusted odds ratios (ORs)* of miscarriage according to the presence of chronic conditions prior to the start of pregnancy (n = 593,009).

*The ORs are adjusted for the woman’s age at the start of pregnancy as a linear and a squared term.

Among the other categories, a few conditions showed strong associations, including hypoparathyroidism (OR 2.58; 95% CI: 1.35 to 4.92; p-value 0.004), Cushing syndrome (OR 1.97; 95% CI: 1.06 to 3.65; p-value 0.03), Crohn’s disease (OR 1.31; 95% CI: 1.18 to 1.45; p-value <0.001), and type 1 diabetes (OR 1.11; 95% CI: 1.01, 1.23; p-value 0.04). Adjustment for woman’s age was important for unbiased estimates, as shown by the attenuation of the unadjusted results (S1 Fig). The sensitivity analysis excluding molar pregnancies from the definition of miscarriage showed similar results as the main analysis (S2 Fig).

Adjusted results were largely consistent when stratified by women’s age (dichtomized at age 35) (S3 Fig), with some exceptions. Miscarriage risk was far stronger among older women with atherosclerosis and PCOS than among younger, while the risk of miscarriage associated with Cushing syndrome and hyperparathyroidism was stronger among the younger women.

Women with miscarriages who were seen only by general practitioners were slightly younger (mean 0.8 years) and less likely to have chronic disorders than women seen by specialists (S2 Table). The risk of miscarriage by maternal age was the same for miscarriages identified in the patient and general practitioner databases (S4 Fig). The associations between chronic conditions and risk of miscarriage were confined largely to miscarriages referred to specialist healthcare services (S5 Fig).

The risk of miscarriage was higher if a woman had more than one chronic disease. The OR of miscarriage with any one chronic disease was 1.01 (95% CI: 0.99 to 1.04; p-value 0.4), increasing to 1.14 (95% CI: 1.07 to 1.20; p-value <0.001) with any two and 1.49 (95% CI: 1.25 to 1.78; p-value <0.001) with any three (Table 2). The main findings were robust to mutual adjustment for other underlying chronic disorders (S6 Fig).

Table 2

The adjusted* odds ratios (OR) of miscarriage according to number of preexisting chronic conditions registered prior to pregnancy in 593,009 pregnancies.

Number of chronic diseases present before pregnancy	Adjusted* OR	95% CI
0	1.00 (reference)
1	1.01	0.99, 1.04
2	1.14	1.07, 1.20
3 or more	1.49	1.25, 1.78

*Adjusted for the woman’s age at the start of pregnancy.

Discussion

Combining information from 3 national health registries, we found that the risk of miscarriage was largely unaffected by the presence of a chronic disease in the mother. A distinct increase in miscarriage risk was present among women with cardiometabolic diseases and a few other illnesses (Crohn’s disease, Cushing syndrome, hypoparathyroidism, and endometriosis). Women with two or more chronic diseases were at increased risk regardless of their illness.

It has previously been shown that women with a history of miscarriages are at increased risk of subsequent cardiovascular disease [33]. Our data suggest that miscarriage risk does not cause cardiovascular disease, but rather that preexisting cardiometabolic health might influence the risk of miscarriage. We observed a clear pattern of increased miscarriage risk across all 3 diseases included in our category of cardiometabolic diseases (atherosclerosis, hypertension, and type 2 diabetes). One previous study has reported a link between hypertension and miscarriage risk [34], although this has not been consistently found [35]. Previous studies also support an increased risk of miscarriage among women with type 2 diabetes, including 1 case–control study that retrospectively collected information on history of miscarriages, and 2 clinical chart reviews [9,19,20].

Taking these results together, cardiometabolic health seems an important contributor to a successful pregnancy. It is already well established that women with cardiovascular risk factors are at increased risk of preeclampsia and preterm delivery [36]. It would not be surprising if miscarriage risk should be added to this list. Women undergo extensive hemodynamic and metabolic changes during pregnancy, with an increase in blood volume, heart rate, glucose levels, and an altered lipid profile [37-39]. It is plausible that women with poorer cardiometabolic health prior to pregnancy (such as elevated blood pressure or glucose levels) might not adapt as well to pregnancy, rendering them at higher risk of miscarriage. These underlying biological mechanisms deserve further exploration. An increased risk of miscarriage among women with Cushing syndrome could also be related to cardiometabolic mechanisms [23].

A meta-analysis of 9 retrospective studies of women with endometriosis suggested an increased history of miscarriage [40]. A previous prospective study also found an increased risk with endometriosis [41]. A possible biological pathway might be the progesterone resistance in women with endometriosis, leading to dysregulation of genes important in embryo implantation and the subsequent greater risk of pregnancy loss [42,43].

A higher risk of miscarriage among women with Crohn’s disease has not previously been reported, although other autoimmune diseases have been linked to miscarriage risk [7-11,23]. We likewise saw borderline increased risk with other autoimmune conditions. Pregnant women undergo a shift from a Th1 immune profile (which often characterizes autoimmune disorders) to a Th2 profile (which often characterizes allergic disorders), and this shift helps to ensure a successful pregnancy by facilitating an immune tolerance towards the embryo [44,45]. An insufficient immune adaptation during pregnancy may be associated with an increased risk of fetal loss [46].

Limitations and strengths

Our study had important limitations. We acknowledge that the strict definition of miscarriage refers to uterine pregnancies. In our registry study, we defined the outcome as miscarriages or pregnancies that did not survive to 16 weeks; ectopic pregnancies were excluded. We were also unable to adjust for some potential confounding factors. Women’s socioeconomic position and lifestyle characteristics (e.g., body mass index and smoking during pregnancy) have been reported to be associated with the risk of miscarriage [47-49]. Uncontrolled confounding by these factors might have contributed to our results, especially for hypertension and type 2 diabetes. We used E-values to estimate the magnitude of the relationship that any unmeasured confounder would have to have to completely explain away our findings [50]. An unmeasured confounder would have to be associated with a 2-fold increased risk of both miscarriage and type 2 diabetes to completely attenuate their observed association, while the unmeasured confounder would have to be associated with a 1.74 increased risk of both miscarriage and endometriosis to completely attenuate their observed association. We were able to identify only miscarriages that resulted in contact with healthcare services (primary or secondary healthcare services). Very early miscarriages where the woman did not know she was pregnant or did not choose to seek medical attention could not be included. We also acknowledge that defining pregnancy outcomes based on administrative codes in the registries might have caused misclassification due to our inability to confirm the outcome by clinical examinations. Our findings might also not be generalizable to populations with different ethnic compositions or populations without universal healthcare services. We might have underestimated the number of women with chronic diseases based on information from the registries. This could have resulted in an attenuation of the observed associations due to the presence of chronic diseases also among some women defined as disease free. However, the registration of chronic diseases in the registries have been shown to have a high validity [31,51].

We also did not have information on treatment the women may have been receiving for these conditions, so we cannot distinguish between the effects of underlying diseases and the medications used to treat those diseases. The proportion of women with preexisting chronic conditions is also likely underestimated, as compared with the prevalence of some of these diseases from other pregnant populations [52,53]. This may be due in part to our conservative approach, requiring 2 diagnostic registrations in order to assign a disease to a woman.

In our previous study [32], based on pregnancies in the birth registry and the patient registry, the total risk of miscarriage risk was 13%, which captured miscarriages seen by specialists healthcare services. In the present analysis, we were able to add miscarriages diagnosed by general practitioners, which increased the risk of miscarriage to 16%. While this is at the upper end of the usual range, it is similar to reports from a British general practitioner database [54]. Our study is, to our knowledge, unique in its size (a whole nation), its inclusion of all recognized pregnancies seen by primary or specialist healthcare services, and its basis in recorded medical data.

In conclusion, maternal chronic diseases were largely unassociated with increased risk of miscarriage, although diseases related to cardiometabolic health were consistently linked to elevated miscarriage risk. A better understanding of the potential biological processes underlying these associations might eventually suggest ways to improve pregnancy outcomes.

(DOCX)

Click here for additional data file.

(DOCX)

Click here for additional data file.

Supplementary methods.

(DOCX)

Click here for additional data file.

Diagnostic codes used to define chronic diseases in specialist care (ICD-10 codes), and in primary care (ICPC-2 codes).

(DOCX)

Click here for additional data file.

Prevalence of preexisting chronic diseases prior to pregnancy within miscarriages identified in the specialist and primary healthcare services.

(DOCX)

Click here for additional data file.

Unadjusted odds ratios of miscarriage according to the presence of chronic conditions prior to pregnancy.

(DOCX)

Click here for additional data file.

Adjusted odds ratios of miscarriage according to the presence of chronic conditions prior to pregnancy excluding molar pregnancies.

(DOCX)

Click here for additional data file.

Adjusted odds ratios of miscarriage according to the presence of chronic conditions prior to pregnancy stratified by whether the mother was younger than 35 years (n = 481,579) or 35 years or higher (n = 111,430).

(DOCX)

Click here for additional data file.

Age-associated risk of miscarriage identified in specialist (n = 62,974 pregnancies) or primary (n = 22,702 pregnancies) healthcare services.

(DOCX)

Click here for additional data file.

Adjusted odds ratios of miscarriage according to the presence of chronic conditions prior to pregnancy according to whether the miscarriage was identified in the specialist (n = 62,974 pregnancies) or primary healthcare (n = 22,702 pregnancies).

(DOCX)

Click here for additional data file.

Adjusted odds ratios of miscarriage according to the presence of chronic conditions prior to pregnancy mutually adjusting for other chronic conditions.

(DOCX)

Click here for additional data file.

17 Aug 2020

Dear Dr Magnus,

Thank you for submitting your manuscript entitled "Risk of miscarriage in women with chronic diseases" for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff as well as by an academic editor with relevant expertise and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript within two working days, i.e. by .

Login to Editorial Manager here: https://www.editorialmanager.com/pmedicine

Once your full submission is complete, your paper will undergo a series of checks in preparation for peer review. Once your manuscript has passed all checks it will be sent out for review.

Feel free to email us at plosmedicine@plos.org if you have any queries relating to your submission.

Kind regards,

Artur Arikainen,

Associate Editor

PLOS Medicine

30 Nov 2020

Dear Dr. Magnus,

Thank you very much for submitting your manuscript "Risk of miscarriage in women with chronic diseases" (PMEDICINE-D-20-03922R1) 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 three independent reviewers, including a statistical reviewer (r#1). The reviews are appended at the bottom of this email and any accompanying reviewer attachments can be seen via the link below:

[LINK]

In light of these reviews, I am afraid that we will not be able to accept the manuscript for publication in the journal in its current form, but 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, and we plan to seek re-review by one or more of the reviewers.

In revising the manuscript for further consideration, your revisions should address the specific points made by each reviewer and the 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.

In addition, we request that you upload any figures associated with your paper as individual TIF or EPS files with 300dpi resolution at resubmission; please read our figure guidelines for more information on our requirements: http://journals.plos.org/plosmedicine/s/figures. While revising your submission, please upload your figure files to the PACE digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at PLOSMedicine@plos.org.

We expect to receive your revised manuscript by Dec 21 2020 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.***

We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. 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. If new competing interests are declared later in the revision process, this may also hold up the submission. 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. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

Please use the following link to submit the revised manuscript:

https://www.editorialmanager.com/pmedicine/

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. For instructions see http://journals.plos.org/plosmedicine/s/submission-guidelines#loc-methods.

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,

Emma Veitch, PhD

PLOS Medicine

On behalf of Artur Arikainen, PhD, Associate Editor,

PLOS Medicine

plosmedicine.org

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

Requests from the editors:

*Please revise your title according to PLOS Medicine's style - we'd suggest this includes an indication of the study design (eg, "registry linkage study) in the subtitle (ie, after a colon).

*In the paper the authors define the study as a prospective-registry-based study, however given the analysis uses routinely collected data (the medical birth registry, the Norwegian Patient Registry, and the general practitioner database), presumably the data existed in those registries before the plan to draw them together and analyse them for the purposes of this question, was developed? In which case it might be better to define it as retrospective (in the sense the data existed before the analysis plan)? More clarity on this would be helpful.

*We'd suggest using the RECORD guideline (developed to help reporting of analyses conducted using registry linkage/routinely collected data) - https://www.equator-network.org/reporting-guidelines/record/. In this case please include the completed RECORD checklist as Supporting Information. Please add the following statement, or similar, to the Methods: "This study is reported as per the RECORD guideline (S1 Checklist)". When completing the checklist, please use section and paragraph numbers, rather than page numbers.

*In the last sentence of the Abstract Methods and Findings section, please include a brief note about any key limitation(s) of the study's methodology. Specifically, a reviewer notes that there are major limitations in terms of the ability to adjust for possible (likely) confounders in this study, and this certainly should be mentioned.

*Can the authors clarify at what point the analytical plan used in this paper was developed - 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.

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

Comments from the reviewers:

Reviewer #1: I confine my remarks to statistical aspects of this paper. These were well done. My only concern is about confidence intervals (I am glad the authors did not include p values). But, since the authors have the entire population, what are these CIs? Some people posit a "super-population" of some sort. I'm not a big fan of this, pregnancies in Norway are not a random sample of pregnancies world wide (for one thing, health care is much better there than in almost any other country). But this needs to be addressed.

I'd be fine with no CIs, but others might object.

Peter Flom

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

Reviewer #2: This is a fairly straightforward analysis of whether chronic disease is associated miscarriage. Strengths of the paper are the large, population-based dataset, consistent coding, and careful consideration of analytic issues, such as competing risk due to induced abortion.

The authors discuss the possibility of missing diagnosis of chronic disease, but have less to say about missing diagnosis of miscarriage. Many early miscarriages are not clinically treated, many are probably not reported, and others are not even noticed. The authors discuss the overall incidence and how it compares to other populations, but not this issue. I also don't see discussion of the fact that women under treatment for some conditions may also be more aware of their bodies, or more likely to report to doctors if they do miscarry, particularly for a condition like endometriosis. An additional possible issue is competing risk from subfertility, which might be a cause for the lack of relationship with some outcomes (it is possible that some of the medications used to treat epilepsy could cause very early, i.e. undetectable, losses or infertility.)

The authors do consider the possibility of confounding, which they are able to address only to a limited extent. I would like to see this emphasized a bit more in the abstract.

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

Reviewer #3: This study reports on the prospective risk of miscarriage in women with a preexisting chronic disease based on 6 years of all reported pregnancies in Norway (2010-2016). The study design ensures that the chronic disease is diagnosed prior to the pregnancy loss. The authors also undertake the task of estimating how many of the terminated pregnancies would have ended as a pregnancy loss if not the termination had been undertaken. The study is larger than previous studies, however no new information is given by the study.

Major issues.

Terminology: Miscarriage is per definition a loss of a confirmed intrauterine pregnancy. This requires that the pregnancy has been scanned, identification of villi or fetus in the expelled pregnancy or in the evacuate. The authors use miscarriage despite several of their included pregnancies are not confirmed intrauterine - please instead use pregnancy loss.

Definition: It is unclear why the authors included molar pregnancies in their definition of miscarriage. Please explain.

Selection of chronic diseases: On what basis was chronic diseases included in the analysis - why was Hashimoto thyroiditis not included? Known to be the most common autoimmune manifestation in women of reproductive age and previously found to be associated with the risk of pregnancy loss.

Validation of diagnosis: Please include information of diagnosis validation of the included diagnoses. It is surprising that only 1% of the included women suffer from PCOS. This is the most common endocrine disorder in reproductive aged women and supposed to be as high as 5-10%.

Why are numbers of pregnancy losses (the core of this manuscript) not mentioned in Table 1 as it is in supplementary table 2?

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

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

[LINK]

14 Dec 2020

Submitted filename: 20201213_Response_letter.docx

Click here for additional data file.

19 Jan 2021

Dear Dr. Magnus,

Thank you very much for re-submitting your manuscript "Risk of miscarriage in women with chronic diseases: a Norwegian registry linkage study" (PMEDICINE-D-20-03922R2) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor and it was also seen again by two reviewers. 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 each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and 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.

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 Jan 26 2021 11:59PM.

Sincerely,

Artur Arikainen

Associate Editor

PLOS Medicine

plosmedicine.org

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

Requests from Editors:

1. Please address the reviewer #3’s comment on correct use of terminology – this has also been requested by the Academic Editor. Further consideration of your manuscript is contingent on this being addressed.

2. Title: Please amend to: “Risk of pregnancy loss in women with chronic diseases in Norway: A registry linkage study”

3. Short title: Please amend to: “Chronic diseases and pregnancy loss”

4. Please include line numbers in the margin throughout.

5. Abstract:

a. Please remove “prospectively” here and throughout, since your analysis itself is retrospective.

b. Please remove “retrospective” when describing the study here and throughout, since “registry-based” already implies a retrospective analysis.

c. Please include p values for your comparisons, alongside 95% CIs.

d. At the end of the ‘Methods and findings’ subsection, please state more clearly: “Limitations of this study were…”. You could also mention the rareness of some conditions as a further limitation, eg. Cushing’s syndrome.

e. Conclusions: Please begin with “In this registry study, we found that…”

6. Page 3: Delete keywords.

7. Author Summary: Amend to: “To our knowledge, none of the existing studies have…”

8. Please remove spaces from within citations, eg: “…environmental factors [5,6].”

9. Results: Please include p values for your comparisons, alongside 95% CIs.

10. Discussion: Please amend to: “Our study is, to our knowledge, unique in its…”

11. Pages 17-18: Please remove the Author Contributions, Data Availability Statement, Funding, and Competing interests sections – these are taken from the online submission form.

12. References:

a. Please remove city and country from journal names, eg. “(London, England)”.

b. Please delete this from reference 32: “at www.icmje.org/coi_disclosure.pdf and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.”

c. Please delete this from reference 36: “Copyright 2018, The Author(s).”

13. 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) and REporting of studies Conducted using Observational Routinely-collected Data (RECORD) guidelines (S1 Checklist)." (and rename the file accordingly)

14. When completing the STROBE/RECORD checklist, please use section and paragraph numbers, rather than page numbers.

---

Comments from Reviewers:

Reviewer #1: The authors have addressed my concerns and I now recommend publication

Peter Flom

Reviewer #3: I am highly surprised that this experienced and respected author group in their rebuttal to PLOS MEDICINE have not responded to a reviewer comment and therefore without any notice keep using miscarriage. To use miscarriage, they should be certain that the pregnancy had been confirmed intrauterine. In practical terms had been scanned, or villi had been identified or the fetus had been visible in the bleeding or the pregnancy material. Clinical researchers changed the terminology to pregnancy loss several years ago unless certain that the losses are intrauterine. I think women pregnant with a gestational age <12 and no prior ultrasound scans with a large bleeding prior to or on their way to hospital who present with an empty uterus at ultrasound and no evaluation of the bleeding will be included in this study.

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

[LINK]

23 Jan 2021

Submitted filename: Response_letter.docx

Click here for additional data file.

27 Jan 2021

Dear Dr. Magnus,

Thank you very much for re-submitting your manuscript "Risk of miscarriage in women with chronic diseases: a Norwegian registry linkage study" (PMEDICINE-D-20-03922R3) for review by PLOS Medicine.

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 minor issues that need to be addressed are listed at the end of this email.

***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 each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and 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.

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 Feb 03 2021 11:59PM.

Sincerely,

Artur Arikainen,

Associate Editor

PLOS Medicine

plosmedicine.org

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

Requests from Editors:

1. Title: Thank you for your reply regarding the terminology – this is fine to leave as is, as we discussed. However, please nevertheless amend to the following to better fit our journal style: “Risk of miscarriage in women with chronic diseases in Norway: A registry linkage study”

2. Abstract: Please add some brief summary demographics for participants (eg. age).

3. Results/Figures and Abstract: Please present p values to 3 decimal places consistently, or “p<0.001”.

4. When completing the STROBE/RECORD checklist, please use section and paragraph numbers, rather than line or page numbers (these will change in the final published version).

Comments from Reviewers:

n/a

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

[LINK]

28 Mar 2021

Dear Dr. Magnus,

Thank you very much for re-submitting your manuscript "Risk of miscarriage in women with chronic diseases in Norway: A registry linkage study" (PMEDICINE-D-20-03922R4) for consideration at PLOS Medicine. We apologize for the delay in contacting you: Dr Arikainen has recently left the journal.

I have discussed the paper with editorial colleagues and I am pleased to tell you that, provided the remaining editorial and production issues are fully dealt with, we expect to be able 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. Please take these into account before resubmitting your manuscript.

***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 each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and 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 hope 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.

Please let me know if you have any questions, and we look forward to receiving the revised manuscript shortly.

Sincerely,

Richard Turner PhD

Senior Editor, PLOS Medicine

rturner@plos.org

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

Requests from Editors:

Please amend your data statement to: "Study data are available on application via helsedata.no, subject to the necessary ethics approvals." or similar.

Please make that "risk of miscarriage" at line 57.

Please state early in the Methods section whether the study had a protocol or prespecified analysis plan. Please highlight analyses that were not prespecified.

Our Academic Editor has requested that you deal with referee 3's comment explicitly in your discussion section. We ask that you do this by amending the wording at line 322, and suggest: "Our study had important limitations. We acknowledge that the strict definition of miscarriage refers to uterine pregnancies. In our registry study, we defined the outcome as miscarriages or pregnancies that did not survive to 16 weeks; ectopic pregnancies were excluded." or similar.

***

31 Mar 2021

Submitted filename: Response_Letter.docx

Click here for additional data file.

1 Apr 2021

Dear Dr Magnus,

On behalf of my colleagues and our Academic Editor Dr Myers, I am pleased to inform you that we have agreed to publish your manuscript "Risk of miscarriage in women with chronic diseases in Norway: A registry linkage study" (PMEDICINE-D-20-03922R5) in PLOS Medicine.

We ask you to address two further issues:

If available, please attach your study analysis plan as a supplementary document, referred to around line 106;

There is a sense of imbalance in the current presentation: around lines 50 and 66, for example, there is an emphasis on associations of miscarriage with cardiometabolic conditions, whereas in the Discussion (around lines 280 and 368) the emphasis is more on an absence of associations with chronic conditions, and we suggest amending the wording to harmonise the different parts of your paper.

Before your manuscript can be formally accepted you will also 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.

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,

Richard Turner, PhD

Senior Editor, PLOS Medicine

rturner@plos.org