Routine screening for SARS CoV-2 in unselected pregnant women at delivery.

BACKGROUND: South America has become the epicenter of coronavirus pandemic. It seems that asymptomatic population may contribute importantly to the spread of the disease. Transmission from asymptomatic pregnant patients' needs to be characterized in larger population cohorts and symptom assessment needs to be standardized.
OBJECTIVE: To assess the prevalence of SARS CoV-2 infection in an unselected obstetrical population and to describe their presentation and clinical evolution.
METHODS: A cross-sectional study was designed. Medical records of pregnant women admitted at the Obstetrics & Gynecology department of Clínica Dávila for labor & delivery, between April 27th and June 7th, 2020 were reviewed. All patients were screened with RT-PCR for SARS CoV-2 at admission. After delivery, positive cases were inquired by the researchers for clinical symptoms presented before admission and clinical evolution. All neonates born from mothers with confirmed SARS CoV-2 were isolated and tested for SARS CoV-2 infection.
RESULTS: A total of 586 patients were tested for SARS CoV-2 during the study period. Outcomes were obtained from 583 patients which were included in the study. Thirty-seven pregnant women had a positive test for SARS CoV-2 at admission. Cumulative prevalence of confirmed SARS CoV-2 infection was 6.35% (37/583) [CI 95%: 4.63-8.65]. From confirmed cases, 43.2% (16/37) were asymptomatic. From symptomatic patients 85.7% (18/21) had mild symptoms and evolved without complications and 14.3% (3/21) presented severe symptoms requiring admission to intensive care unit. Only 5.4% (2/37) of the neonates born to mothers with a positive test at admission had a positive RT-PCR for SARS CoV-2.
CONCLUSION: In our study nearly half of pregnant patients with SARS CoV-2 were asymptomatic at the time of delivery. Universal screening, in endemic areas, is necessary for adequate patient isolation, prompt neonatal testing and targeted follow-up.

Introduction

Coronavirus disease 2019 (COVID-19), caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has been defined as a global public health emergency [1]. Six months after the emergence of this novel virus, South America has become the epicenter of COVID-19 pandemic.

It has been proposed that pregnant women should be considered a high-risk population, since gestation itself could be related with several pregnancy-related complications, higher susceptibility to respiratory pathogens and also can generate problems in terms of the spread of the infection due to the multiple interactions with the health-care system [2]. While initial evidence suggests that pregnant women were not at increased risk for COVID-19, neither developed a more severe disease compared to non-pregnant adults [3, 4], recent reports suggest increased rates of preterm birth [5], pneumonia and intensive care unit admission [6], and maternal mortality [6, 7].

Currently, it has become evident that asymptomatic-people dissemination may play an important role in the spread of the virus [8]. The reported rates of asymptomatic pregnant women ranges from 43% to 89%, with estimates from 4 to 9 undetected cases per each symptomatic patient, supporting universal screening as a possible strategy [9-15]. It is also well established that pregnant women keep their pregnancy supervised by healthcare professionals, allowing close follow-up of their clinical conditions. Therefore, it has been proposed that women admitted for delivery could provide a potential study group with useful estimates of virus circulation among general population [12, 13, 16]. Given the possibility there is a higher prevalence of SARS CoV-2 infection than reported just by symptoms, screening of unselected population may give a more accurate estimate. The former, becomes clinically relevant due to administration of personnel protection measures, proper patient isolation, prompt neonatal testing and targeted follow-up.

The main objective of this study was to assess point-prevalence of SARS CoV-2 infection in unselected obstetrical population at the time of delivery and to describe the presentation and clinical evolution of confirmed cases.

Methods

Setting

The study was conducted at the Obstetrics & Gynecology Department of Clínica Dávila, Santiago, Chile. Our institution is a private healthcare center that provides obstetrical care to nearly 5000 pregnant women per year. It is currently one of the largest obstetrics facilities in our country.

Study design and participants

All pregnant women admitted to labor & delivery between April 27th and June 7th, 2020, with no history of SARS CoV-2 disease during gestation were included. At admission triage, all women were screened for COVID-19 clinical symptoms including fever, cough and shortness of breath by trained personnel, and RT-PCR for SARS CoV-2 (Allplex 2019-nCoV Assay [17]) was performed by nasopharyngeal swab, unless a prior test with no more than 48 hours to admission was reported. Clinical management was carried out with Personal Protective Equipment levels C or D following recommendations [18], until RT-PCR for SARS CoV-2 report was provided.

After delivery, patients with a positive RT-PCR for SARS CoV-2 were inquired by researchers for clinical symptoms presented before the diagnosis (fever ≥ 37.8, cough, headache, shortness of breath, myalgia, odynophagia, nasal congestion, digestive symptoms (diarrhea / vomiting), anosmia, dysgeusia, anorexy) and followed-up for clinical evolution. (S1 Appendix) Following institutional guidelines, neonates born from mothers with the diagnosis of COVID-19, regardless of symptoms, were isolated and SARS CoV-2 RT-PCR was performed at 6 hours and 48–72 hours after delivery. Patients with history of COVID-19 confirmed by RT-PCR during pregnancy, or with less than 24 weeks of gestational age at admission were excluded.

The main objective was to establish the point-prevalence of SARS CoV-2 infection in our obstetrical population at delivery. Secondary objectives were: i) describe the rate of newborns confirmed with positive RT-PCR for SARS CoV-2; ii) evolution of confirmed cases; iii) frequency of adverse maternal outcomes (maternal intensive care unit admission, need of invasive ventilatory support, maternal death); iv) frequency of adverse perinatal outcomes (preterm birth, small for gestational age, 5 minute Apgar < 7, admission to neonatal intensive care unit, perinatal death). This study was approved by the Institutional review board of Clínica Dávila, and a waiver of consent was granted.

Sample size estimation

To estimate the point-prevalence of SARS CoV-2 infection at the time of delivery, a sample size estimation was performed based on the following statistical assumptions: i) a target population of unknown size; ii) 95% confidence intervals; iii) precision of the prevalence estimator of 2.5%; iv) expected point-prevalence of 10% or less. Previous reports in literature have reported point-prevalence’s that ranged from 15.4% to 19.9% in obstetric population [7, 8, 11]. At the time this study was conceived, the national SARS CoV-2 incidence in Chile was in its initial stages; therefore a prevalence of 10% or less was considered plausible for our target population. The estimated sample size required to assess the prevalence of disease was 553 pregnancies. Assuming a maximum loss to follow-up of 5% throughout the study, a final sample of 583 patients was expected to be included. Based on the number of deliveries in our facility, we estimated that the entire sample required would be successfully obtained in a six-week period.

Statistical analysis

In quantitative variables, normality of distribution was assessed using Shapiro—Wilk normality test, and homogeneity of variances between groups was tested using Levene´s test. In variables fitting a Gaussian distribution, comparisons between groups were made using Student´s T-test (with adjustment for unequal variances if necessary). In variables not fitting a Gaussian distribution, Mann-Whitney U-test was used for comparisons. Comparison of categorical variables between groups was performed using Chi-square test or Fisher´s exact test as appropriate.

The overall prevalence of confirmed SARS CoV-2 infection at delivery was described using 95% confidence intervals. Estimates of prevalence were also obtained for each of the six weeks of the present study. The daily screening positivity rate observed in the study, and the daily-incidence rate in the city of Santiago (reported by the Ministry of Health) [19] were modeled using 5-period moving averages time series. Correlation between the observed screening positivity rate and the daily-incidence rate reported in the city of Santiago was estimated using Spearman's rho correlation coefficient.

Maternal and perinatal outcomes were described using absolute frequencies (percentages) and means (standard deviations). Odds ratios and mean differences were used to compare outcomes between groups. In categorical variables, risk estimations were calculated using simple or multivariate logistic regression analysis accounting for potential covariables if appropriate. In numerical variables, mean differences between groups were estimated using simple or multiple linear regression models, accounting for potential covariables if considered necessary.

Two-sided p-values of less than 0.05 were considered statistically significant. The statistical package used for analysis was Stata v.14.2 (StataCorp. 2015 Stata Statistical Software: Release 14. College Station, TX: StataCorp LP, USA)

Results

Sample description

A total of 586 patients were admitted and tested for SARS CoV-2 during the study period. Three cases were excluded: one was less than 24 weeks at the time of admission and the other two cases were term pregnancies, who had a previous diagnosis of COVID-19, with complete quarantine for 14 days, and no longer considered as active cases.

Finally, a total of 583 patients who delivered 586 newborns were included. Among them, 37 had a positive result for SARS CoV-2 at admission. Mean maternal age was 30.3 years and 48.9% of patients were nulliparous. Nearly 16% of our population presented at least one described risk factor for severe disease [20]. Overall, there were no significant differences between confirmed cases and controls in any of the maternal characteristics (Table 1).

Table 1

Main characteristics of the study population at admission.

	Confirmed SARS CoV-2 Infection. (N = 37)	Controls. (N = 546)	P-value.
Maternal age (years)	29.9 ± 6.4	30.4 ± 5.7	0.624
Twin gestations	0 (0.0)	3 (0.6)	-
Primiparous	19 (51.3)	266 (48.7)	0.756
Previous Cesarean Section	5 (13.5)	127 (23.3)	0.170
Maternal body mass index ≥30	5 (13.5)	74 (13.6)	0.995
Chronic Hypertension	0 (0.0)	8 (1.5)	-
Asthma	0 (0.0)	3 (0.6)	-
Pre-gestational diabetes mellitus	1 (2.7)	9 (1.7)	0.484
Active smoker	0 (0.0)	2 (0.4)	-

Data is presented as: means (± standard deviations) or absolute frequencies (%).

Screening findings

During the 6 weeks study period, the cumulative prevalence of confirmed SARS CoV-2 infection was 6.35% [CI 95%: 4.63–8.65]. Interestingly, we were able to observe a progressive increase in the rate of positive tests, starting with a point prevalence of 3.03% (3/96) during the first week and reaching an 8.89% (8/82) during the last week of the study. When we compared the daily positivity rate observed in our study group with the daily-incidence rate reported in Santiago de Chile, there was a statistical significant positive correlation between them (rho: 0.559, p-value < 0.001) (Fig 1), meaning that during the same period of time, regional incidence rate showed similar trends.

Fig 1

Screening performance per study week related to daily case incidence in Santiago de Chile.

Case description and maternal outcomes

From the 37 confirmed cases, 43.2% (16/37) were asymptomatic and 56.8% (21/37) were symptomatic at admission. Table 2 summarizes the characteristics of these patients.

Table 2

Case description of patients with a positive RT-PCR for SARS CoV-2 at admission.

	Maternal outcomes						COVID-19 symptoms*		Newborn outcomes
Case #	Maternal Age	Symptomatic at Admission	Hospitalization (days)	Mechanical ventilation (days)	Oxygen requirement (days)	Admission Diagnosis	Spontaneously referred	At entry survey	GA (weeks, days)	BW (gr)	Apgar 1'	Apgar 5'	RT PCR for SARS COV-2 (6 & 48–72 hours)	Neonatal Unit admission**	Perinatal death
1	28	No	3				-	-	39 (2/7)	3660	9	9	-	-	-
2	41	Yes	13	0	9	ARI	-	+	37 (0/7)	2915	NE	NE	-	-	-
3	41	No	3				-	-	37 (5/7)	3110	9	9	-	-	-
4	35	No	3				-	-	39 (4/7)	3365	9	10	-	-	-
5	26	No	3				-	-	39 (5/7)	4170	9	10	-	-	-
6	23	No	3				-	+	38 (2/7)	2820	8	9	-	-	-
7	21	No	3				-	-	39 (0/7)	3150	9	10	-	-	-
8	30	No	3				-	+	39 (3/7)	2410	8	8	-	-	-
9	39	No	3				-	+	40 (2/7)	3840	9	9	+	-	-
10	42	No	3				-	-	39 (1/7)	3335	9	9	-	NIMCU	-
11	24	No	3				-	+	40 (3/7)	3590	9	9	-	-	-
12	27	No	3				-	+	38 (4/7)	3510	9	10	+	-	-
13	32	No	3				-	-	39 (2/7)	4530	9	10	-	-	-
14	38	No	3				-	+	38 (4/7)	3550	9	9	-	-	-
15	32	No	3				-	-	38 (5/7)	3630	9	9	-	-	-
16	27	Yes	18	10	14	ARI	+	+	38 (0/7)	2740	4	8	-	-	-
17	25	No	3				-	-	40 (3/7)	3375	9	10	-	-	-
18	31	No	3				-	-	38 (3/7)	3260	9	9	-	-	-
19	31	No	3				-	-	40 (4/7)	3630	9	9	-	NIMCU	-
20	27	No	3				+	+	39 (5/7)	3720	9	10	-	-	-
21	29	No	3				+	+	40 (2/7)	3310	9	9	-	-	-
22	25	No	3				-	-	37 (0/7)	2620	9	9	-	NICU	+
23	40	Yes	6	1	5	ARI	+	+	30 (0/7)	1850	1	5	-	NIMCU	-
24	25	No	3				-	+	38 (5/7)	3130	9	9	-	-	-
25	26	No	7			FGR	-	+	35 (0/7)	1965	9	9	-	NIMCU	-
26	39	No	3				-	-	38 (3/7)	3030	9	9	-	-	-
27	22	No	3				+	+	40 (0/7)	3125	9	10	-	-	-
28	20	No	3				+	+	36 (5/7)	2880	8	9	-	-	-
29	23	No	3				-	-	40 (1/7)	3355	9	9	-	-	-
30	17	No	4				-	+	38 (5/7)	3225	9	9	-	-	-
31	31	No	3				-	+	38 (0/7)	2745	9	9	-	-	-
32	32	No	5				-	-	39 (0/7)	3215	9	9	-	-	-
33	32	No	4				-	+	40 (0/7)	3465	9	9	-	-	-
34	26	No	4				-	-	39 (4/7)	3490	8	9	-	-	-
35	31	No	3				-	+	38 (2/7)	3720	7	9	-	-	-
36	34	No	3				-	+	36 (1/7)	2650	9	9	-	-	-
37	32	No	4				-	+	39 (5/7)	3385	9	9	-	-	-

“GA”: Gestational age; “BW”: Birthweight; “ARI”: Acute respiratory insufficiency; “FGR”: Fetal growth restriction; “NE”: Not evaluated.

* at least one symptom.

** Admission to Neonatal Intensive Care Unit (NICU) or Neonatal Intermediate Care Unit (NIMCU).

Among symptomatic cases, 71.4% (15/21) mentioned no symptoms at admission. However, after a structured interview was applied, they referred at least one symptom present during the previous days and were classified as symptomatic cases. S1 Fig shows symptom distribution according to patient survey.

Based on COVID-19 disease severity characteristics by Wu et al. [21] of symptomatic cases, 85.7% (18/21) had mild symptoms and evolved positively during hospitalization. The other 14.3% (3/21) presented severe symptoms and required admission to intensive care unit. Of them, 2 required invasive ventilatory support, representing 9.5% (2/21) of symptomatic cases and 5.4% (2/37) of all confirmed cases. There were no maternal deaths during the study period.

Perinatal outcomes

Overall, the mean gestational age at delivery was 38.8 weeks of gestational age, and the rate of preterm birth (<37 weeks of gestational age) was 5.29% (31/586). Mean birthweight was 3337.1 grams and the rate of small for gestational age newborns (<10th centile) was 5.12% (30/586). There were 49.5% (290/586) cesarean sections, and 10.1% (30/296) instrumental deliveries. Mean Apgar score at 1 and 5 minutes was 9, and the rate of low Apgar (<7 at 5 minutes) was 0.8% (5/585). Overall, there were no differences between confirmed cases and controls for each outcome evaluated Table 3 summarize main perinatal outcomes and S1 Table compares results among symptomatic and asymptomatic cases.

Table 3

Main perinatal outcomes.

	Confirmed SARS CoV-2 Infection. (N = 37)	Controls. (N = 549)	Estimated effect (IC 95%)	P-value.
Gestational age at delivery (weeks)	38.6 (± 1.9)	38.8 (± 1.7)	Mean Difference: 0.265 (-0.304 to 0.834)	0.361
Preterm birth	4 (10.8)	27 (4.9)	OR: 2.34 (0.77–7.10)	0.132
Birthweight (grams)	3344 (± 506)	3231 (± 532)	Mean Difference: 112.9 (- 56.5 to 282.2)	0.191
Small for gestational age	2 (5.4)	28 (5.1)	OR: 1.06 (0.24–4.65)	0.935
Cesarean delivery	18 (48.7)	272 (49.5)	OR: 0.96 (0.50–1.88)	0.916
Instrumental vaginal delivery	1 (2.7)	29 (5.3)	OR: 0.50 (0.07–3.76)	0.499
5th minute Apgar Score ≤ 7	1 (2.8)	4 (0.7)	OR: 2.47 (0.23–26.07)	0.451 (a)
Neonatal admission	5 (13.5)	28 (5.1)	OR: 2.45 (0.72–8.36)	0.154 (a)
Perinatal death	1 (2.7)	3 (0.6)	OR: 4.27 (0.41–43.90)	0.223 (a)

Data is presented as: means (± standard deviations) or absolute frequencies (%).

(a) Estimated effects adjusted by preterm delivery.

During the study period, there were 33/586 (5.6%) newborns who required neonatal admission (either Neonatal Intensive Care Unit or Neonatal Intermediate Care Unit). Among them, 5 cases were deliveries from RT-PCR positive patients; newborn from case #10 was admitted due to cyanosis; newborn from case #19 was admitted due to transient tachypnea; newborn from case #22 was admitted due to septic shock; newborn from case #23 was admitted due to 30 weeks preterm birth; newborn from case #25 was admitted due to prenatal diagnosis of early fetal growth restriction. All of them presented a negative RT-PCR for SARS CoV-2.

Among 37 confirmed maternal cases, all newborns were initially isolated. Of them 94.6% (35/37) had a negative RT-PCR for SARS CoV-2 analysis at 6 and 72 hours after delivery. There were 2 (5.4%) newborns, both from asymptomatic mothers, who presented a positive RT-PCR for SARS CoV-2 at 6 and 72 hours, both were kept in isolation during maternal admission, evolved without symptoms, and were discharged to complete domiciliary quarantine with their mothers.

During our study four perinatal deaths were registered, 2 stillbirth and 2 neonatal death. Of the stillbirths, both mothers had a negative RT-PCR for SARS CoV-2. The first one occurred at 38 weeks and was attributable to a prenatal diagnosis of trisomy 18. The second, was a perinatal death at 40 weeks of gestational age, without any referable cause at the moment of this report. Of the neonatal deaths, the first one was a spontaneous preterm birth of 27 weeks who died after 6 hours of delivery, with negative maternal RT-PCR for SARS CoV-2 but findings consistent with severe connatal infection. The second one was a newborn delivered at 37 weeks of gestational age, from a patient with a positive RT-PCR for SARS CoV-2 at admission (case #22), who rapidly evolved with a septic shock and died after 26 hours. The neonatal RT-PCR for SARS CoV-2 taken at 6 hours of life was negative. Finally, based on a positive blood culture, neonatal death was attributed to a severe sepsis caused by Streptococcus agalactiae.

Discussion

Principal findings

Our study on universal screening among unselected obstetrical population reveals an overall prevalence of 6.35% of SARS-CoV-2 infections at delivery. Interestingly, nearly half of these cases were asymptomatic at the time of delivery, and of the symptomatic cases nearly 70% referred symptoms only after a targeted interrogation. The later, demonstrates a not negligible reporting bias among patients with very mild symptoms.

Results in the context of what is known

It could be argued that previous reports on universal screening in obstetrics population do not provide information on the local situation of the pandemic, so it is difficult to estimate the real implications and external validity of their findings. Moreover, as it has been stated, the different time points of patient recruitment along with the rising and falling phase of the pandemic curve, explain the different rates of positive RT‐PCR results [22]. Therefore, in areas with high prevalence of infection, it could be expected that more women may be positive but asymptomatic [23]. This could be seen in reports by Sutton et al. [10], Vintzileos et al. [9], Bianco et al. [13] and Dória et al. [16] All of them were conducted in areas and timepoints with reported high prevalence of infection [24], and showed higher observed SARS-CoV-2 infection prevalence, ranging between 11 and 19%, with up to 15% of asymptomatic confirmed cases among screened population. On the other side, reports by Naqvi et al. [25] and Gagliardi et al. [12], reported a low performance of universal screening based either on an overall lower disease burden in their region or due to a referred “steady state” of virus circulation, with less than 1% of asymptomatic confirmed cases. In an intermediate epidemiological situation [24] reports by Khalil et al. [11], Miller et al. [14] and Ochiai et al. [26] presented observed SARS-CoV-2 infection prevalence ranging between 3 and 7%, with up to 6% of asymptomatic confirmed cases among screened population, which are similar to our findings.

In our study, at the moment of the initial recruitment, according to the official data reported by the National Ministry of Health, there were about 7858 confirmed cases of SARS CoV-2 in the city of Santiago, with a cumulative incidence of 96.7 per 100000 habitants. In the following weeks, there was a progressive increase in daily incidence, reaching at the end of our study a total of 112136 confirmed cases and a cumulative incidence of 1380 per 100000 habitants. The above explains the increase in cases in our obstetrical population registered during the study period. According to our results, it could be argued that current rates of SARS CoV-2 infection among general population are underestimated, and this is only partially explained by asymptomatic cases.

Regarding asymptomatic population, almost all previous studies report higher rates of asymptomatic patients [9–13, 16, 26]. This could be explained by how case definition changed as the pandemic evolved, leading to a non-standardized definition in literature, and by differences among studied populations. Also, the extent of symptom evaluation at admission is a key factor in the reported prevalence of asymptomatic patients. In our study there was a high rate of reporting bias (patients not referring symptoms spontaneously but with positive ones when a targeted anamnesis was applied) of nearly 70%. This could be due to the fact that a significant number of symptoms of COVID-19 disease overlap with those related to physiological changes during pregnancy. The above highlights the importance of targeted symptom assessment, the need of proper patient education on signs & symptoms and the potential limitation of a diagnostic strategy based only in patients’ symptoms report.

Regarding perinatal outcomes, we found no significative differences between groups. It's important to highlight that our study was not designed to assess the differences in perinatal outcomes, so careful interpretation should be taken. However, we did notice a trend to a higher rate of preterm birth among our study population, which is in line with recent reports [5, 27–30]. We also had an unexpected high rate of perinatal death, but after analyzing each case individually, causal association with SARS CoV-2 infection seems unlikely.

Clinical implications

Taking into account our findings and the available literature, in endemic areas, it seems reasonable to perform universal screening for SARS CoV-2 infection to all patients admitted in labor as it detects an important percentage of patients that would not be detected by conventional clinical screening based only in clinical manifestations of the disease. Moreover, when compared against data reported by the National Ministry of Health, trends among our obstetric population may be a reflection of what was happening in the city of Santiago at the same time. As it has been suggested that there is a strong possibility that community infection prevalence may far exceed what is currently being reported [14]. So, universal screening to obstetric population may provide insight to estimates general population prevalence of SARS CoV-2 infection.

Research implications

Real implications of COVID-19 disease in the obstetrics population are still largely unknown. So far, conclusions drawn from available literature are reasonably hindered by the context of an evolving pandemic and different approaches across nations. Until larger nation-based reports are available, definitive conclusions cannot be made.

Also, given the consistently high rates of asymptomatic infection, implications and long-term outcomes among this non-identified subset of “recovered” ongoing pregnancies (and their newborns) are somehow alarming. Serological assessment at third trimester as a way of screening for this population could be considered, yet several issues such as cross reactivity, antibody kinetics and cost effectiveness remain to be resolved [31].

Strengths and limitations

The main strength of our study is that our institution is one of the largest obstetric centers in our country allowing to gather a large sample of patients’ representative of local population in a short period of time. This is important due to the unpredictable behavior of the pandemic. Also, to the best of our knowledge, this is one of the largest reports on universal screening in unselected obstetrics population. We also acknowledge several limitations: First, we were not able to assess for maternal serologic status, therefore we cannot rule-out that some of our patients may already have recovered from an asymptomatic infection. Second, we did not perform an active follow-up, including targeted anamnesis, of non-infected cases, so we are not able to assess if some proportion of our patients were at early stages of incubation and developed the disease after being discharged from our institution. Third, several sources of variability have been reported from RT-PCR obtained from nasopharyngeal swab [32], so the possibility of false negative results in our patients, especially those who were asymptomatic at admission could not be discarded, and point prevalence could be underestimated. Bronchoalveolar lavage has been reported to present higher sensibilities than nasopharyngeal swab [33], but the use of invasive (high-risk aerosolizing) diagnostic measure seems disproportionate in the context of asymptomatic population. Also, it has been reported that non-enhanced chest CT presents higher sensibilities than RT-PCR [34]. However, according with current recommendations of the American College of Radiology (ACR) [35], we did not perform on systematic basis imagenologic studies to all patients. Finally, regarding newborns with confirmed infection, we did not perform amniotic fluid nor placental analysis, therefore we are not able to establish any conclusion regarding potential vertical transmission.

Conclusion

The point prevalence found in our study is 6.35%, with nearly 50% of them being asymptomatic. Universal screening in unselected population at delivery, should be considered in endemic areas as provide good estimates of population-level prevalence of SARS CoV-2 infection, allowing adequate with protection of health team, proper patient isolation, prompt neonatal testing and targeted follow-up.

Symptom distribution according to patient survey.

(TIFF)

Click here for additional data file.

Entry survey (for confirmed cases).

(DOCX)

Click here for additional data file.

Maternal and pregnancy outcomes, according to presence of clinical symptoms in patients with positive RT-PCR for SARS CoV-2 infection.

(DOCX)

Click here for additional data file.

29 Jul 2020

PONE-D-20-20646

Routine screening for SARS CoV-2 in unselected pregnant women at delivery.

PLOS ONE

Dear Dr. Caradeux,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Three expert reviewers handled your manuscript. We are very thankful for their time and efforts. Although some interest was found in your study, several major concerns overshadowed this enthusiasm. These concerns relate to the need to state a proper rationale and directional hypothesis; there are questions about group comparisons and the need to detail whether there were other complications in these women; more specifics should be provided about some of the methods, including symptoms used to characterize SARS-CoV-2 infection; there are suggestions to improve the data presentation; and the discussion needs to be more developed based on inclusion of additional supportive publications from the literature. Please address all of the reviewers' comments in your revised manuscript.

Please submit your revised manuscript by Sep 12 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Frank T. Spradley

Academic Editor

PLOS ONE

Journal requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for stating in the text of your manuscript "This study was approved by the Institutional review board of Clinica Davila.". Please also add this information to your ethics statement in the online submission form.

3. Please include additional information regarding the structured interview guide used in the study (line 167 of manuscript) and ensure that you have provided sufficient details that others could replicate the analyses. If it is not under a copyright more restrictive than CC-BY, please include a copy, in both the original language and English, as Supporting Information.

4. Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

Reviewer #3: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The paper is well written, however, the author needs to give the paper a purpose, give good scientific reasons to what their findings implicate. They also have to try and investigate further on the cases where the babies were born with the virus. They did not specify whether the babies were born from mothers with asymptomatic covid-19, mild symptomatic covid-19 or the aggressive type. This is a very important point that may explain the vertical transmission.

Also, the authors need to state whether the mothers had other complications besides covid-19. This could explain the difference in the aggressiveness of the virus among the women.

Reviewer #2: This is a relevant paper. The pandemic is rapidly increasing in Latin American countries and more information is needed to provide the best possible care for pregnant women. There have been some articles about universal COVID-19 screening in pregnant population, none of the in Latin American countries to the best of my knowledge, and there is still a lot of disparities in data worldwide and a lot that we still don't know about this virus and its implications during pregnancy. Early diagnosis and proper management could make a difference in outcomes . Other interesting points include the pandemic growth visualization as the same time as positive pregnant cases are increasing; and detailed fetal outcomes including reasons for intensive care unit admission.

Some considerations for the authors:

(1) In my opinion, one of the most interesting innovations of the study is a structured interview on maternal symptoms, leading to an important drop in the number of asymptomatic pregnant women. The questionnaire (anex) was applied after birth, but I could not understand if the woman was asked only about symptoms previous to birth or whether symptoms that started after delivery were also reported. Also, how the symptoms onset information (if available) was treated by the authors. I would suggest that this specific aspect should be addressed in the Discussion using previous reports of universal screening programs as reference. Did other authors report how they assessed symptoms? Would an approach like the one adopted in your study impact the very high prevalence of asymptomatic pregnant women we are seeing in studies from US(Campbell et al 2020, Sutton et al 2020, Vintzileos et al 2020), UK (Khalil et al 2020), Japan (Ochiai et al 2020), Portugal (Doria et al 2020), etc.?

This issue of differences in prevalence of asymptomatic cases depending on the assessment method should appear objectively in the abstract. It may be an important tool that might be used by others in triage or upon admission to improve symptoms screening process until further studies. You could explore this better in the Discussion section and mention the need of furthers studies to examine accuracy, etc.

(2) In the introduction around line 58 when referring that pregnant women are not at increased risk of the disease, it is interesting to state that, regardless initial reports affirming that, near misses and maternal deaths with COVID-19 have been reported in several countries worldwide, including Brazil (Takemoto et al 2020) and Mexico (Lumbreras et al 2020) in the LAC region. Additionally, reports from the US CDC (Ellington et al 2020) and Sweden health authority (Collin et al 2020) observed an increased risk of ICU admission and mechanical ventilation in pregnant vs non-pregnant women;

(3) Figure 1 is remarkably interesting, but the image definition in the version I received is poor. I also believe that there is some repetition of data in both this Figure and Table 2. Maybe figure would be sufficient given that you include the absolute numbers with the corresponding percentages, being an easier way to visualize the information;

(4) In Results, it would be better if you include both n and percentages (ex line 149);

(5) Line 189 and Table 4: In my opinion, Apgar scores should be presented as dichotomous variable outcome (not means), or medians with IQR. Mean Apgar score is not something really useful for readers, for example if you have one Apgar 1 and one Apgar 10, the mean would be 5. What does this actually mean?

Reviewer #3: The authors analyzed nearly 600 patients admitted to the gynecology and obstetrics department in an area endemic to SARS-CoV-2. Although the SARS-CoV-2 has been spreading for months, the real impact on pregnancy is still to be defined, therefore new epidemiological data are welcome in this context.

This report appears to be methodologically correct, but I have some comments to improve the article:

-“Nonetheless, 59 available evidence suggests that pregnant women are not at increased risk for COVID-19, 60 neither develop a more severe disease compared to non-pregnant adults.(3,4)”

This statement appears too strong and the data reported in the literature are conflicting. This statement could lead the reader of this article to underestimate the impact of COVID-19 in pregnancy. Please consider expanding this point on the basis of works that also suggest a negative impact on pregnancy compared to the general population

Consider this papers (for examples):

-Pregnant and postpartum women with SARS-CoV-2 infection in intensive care in Sweden. https://doi.org/10.1111/aogs.13901

-Severe maternal morbidity and mortality associated with COVID-19: The risk should not be down-played. https://doi.org/10.1111/aogs.13900

- The tragedy of COVID‐19 in Brazil: 124 maternal deaths and counting. https://doi.org/10.1002/ijgo.13300

-“During the same 159 period of time, national and regional incidence rate showed similar trends.”

Please add a reference on this important issue and report here the cumulative prevalence in the general population in the same period (I read that this data is reported in discussion section, but it would be useful to report it here too, furthermore is referred only to the city of Santiago).

-Please, in the method section, you should report which symptoms were considered suggestive for SARS-CoV-2. The different symptoms should be reported as a percentage in the results.

-Although the numbers of positive pregnant women are relatively low, is it possible to have comparison between the asymptomatic and the symptomatic about the maternal and the fetal outcomes? Maybe it can be presented as supplementary material with a short comment in the main text.

- The data of the work by Sutton et al are rightly reported in your paper, but the discussion should be enriched considering similar works from other geographic realities, for example consider these for a comparison with your experience:

COVID-19 infection among asymptomatic and symptomatic pregnant women: Two weeks of confirmed presentations to an affiliated pair of New York City hospitals DOI: 10.1016/j.ajogmf.2020.100118

The "scar" of a pandemic: cumulative incidence of COVID-19 during the first trimester of pregnancy. DOI: 10.1002/jmv.26267

Characteristics and outcomes of pregnant women admitted to hospital with confirmed SARS-CoV-2 infection in UK: national population based cohort study DOI: 10.1136/bmj.m2107

COVID-19 Obstetrics Task Force, Lombardy, Italy: Executive management summary and short report of outcome DOI: 10.1002/ijgo.13162

-Clarify that universal screening should be performed only in endemic areas. In places where the coronavirus is not endemic it would be just a waste of resources.

- The references do not follow the instructions of the authors. Please correct them.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (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. Registration is free. 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 PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

24 Aug 2020

Dear Editor & reviewers, we are grateful for the opportunity to improve our manuscript according to the reviewers suggestions. Please find below and itemized answers to all the reviewers queries.

Reviewer #1:

- The paper is well written, however, the author needs to give the paper a purpose, give good scientific reasons to what their findings implicate.

According to the reviewer suggestion, this paragraph has been included in the manuscript introduction. “Given the possibility there is a higher prevalence of SARS CoV-2 infection than reported just by symptoms, screening of unselected population may give a more accurate estimate. The former, becomes clinically relevant due to administration of personnel protection measures, proper patient isolation, prompt neonatal testing and targeted follow-up.”

- They also have to try and investigate further on the cases where the babies were born with the virus. They did not specify whether the babies were born from mothers with asymptomatic covid-19, mild symptomatic covid-19 or the aggressive type. This is a very important point that may explain the vertical transmission.

We fully agree with the need for more research on vertical transmission. However, as stated in our study limitations, we did not perform direct placental nor amniotic fluid assessment so we are not able to draw any conclusion from our results. Regarding babies with positive RT-PCR for SARS COV-2 both were born from asymptomatic mothers, the former has been clarified in the manuscript. Table 3 also details which cases were symptomatic at admission.

The following has been added on the manuscript “Among 37 confirmed maternal cases, all newborns were initially isolated. Of them 94.6% (35/37) had a negative RT-PCR for SARS CoV-2 analysis at 6 and 72 hours after delivery. There were 2 (5.4%) newborns, both from asymptomatic mothers, who presented a positive RT-PCR for SARS CoV-2 at 6 and 72 hours, both were kept in isolation during maternal admission, evolved without symptoms, and were discharged to complete domiciliary quarantine with their mothers.”

- Also, the authors need to state whether the mothers had other complications besides covid-19. This could explain the difference in the aggressiveness of the virus among the women.

We agree with the reviewer's concern. However, this study was designed as a prevalence study, so details regarding maternal obstetric-related outcomes (e.g preclampsia) were out of the scope of this report. Moreover, maternal outcomes among our population are part of a larger multicenter ongoing collaborative study. So, in the light of the above we would prefer not to extend on this topic.

Reviewer #2:

- In my opinion, one of the most interesting innovations of the study is a structured interview on maternal symptoms, leading to an important drop in the number of asymptomatic pregnant women. The questionnaire (anex) was applied after birth, but I could not understand if the woman was asked only about symptoms previous to birth or whether symptoms that started after delivery were also reported.

This is has been clarified according to suggestion, both on the Abstract and Methods section

“After delivery, patients with a positive RT-PCR for SARS CoV-2 were inquired by researchers for clinical symptoms presented before the diagnosis (fever ≥ 37.8, cough, headache, shortness of breath, myalgia, odynophagia, nasal congestion, digestive symptoms (diarrhea / vomiting), anosmia, dysgeusia, anorexy) and followed-up for clinical evolution. (S1 Appendix)”

- Also, how the symptoms onset information (if available) was treated by the authors. I would suggest that this specific aspect should be addressed in the Discussion using previous reports of universal screening programs as reference. Did other authors report how they assessed symptoms? Would an approach like the one adopted in your study impact the very high prevalence of asymptomatic pregnant women we are seeing in studies from US(Campbell et al 2020, Sutton et al 2020, Vintzileos et al 2020), UK (Khalil et al 2020), Japan (Ochiai et al 2020), Portugal (Doria et al 2020), etc.?

This has been taken into account and added in the discussion section (“Results in the context of what is known” and “Strengths and limitations”) as follows: “While most previous studies report higher rates of asymptomatic patients, [10,11,21] one reports significantly less asymptomatic positivity rates.[22] This could be explained by how the definition of case changed as the pandemic evolved, leading to no standardized definition in literature, and by differences among studied populations. Also, the extent of symptom evaluation at admission is a key factor in the reported prevalence of asymptomatic patients. In our study there was a higher rate of reporting bias (patients not referring symptoms spontaneously but with positive ones when a targeted anamnesis was applied) of nearly 70%. This could be due to the fact that a significant number of symptoms of COVID-19 disease overlap with those related to physiological changes during pregnancy. The above highlights the importance of targeted symptom assessment, the need of proper patient education on signs & symptoms and the potential limitation of a diagnostic strategy based only in patients’ symptoms report.”

- This issue of differences in prevalence of asymptomatic cases depending on the assessment method should appear objectively in the abstract. It may be an important tool that might be used by others in triage or upon admission to improve symptoms screening process until further studies. You could explore this better in the Discussion section and mention the need of further studies to examine accuracy, etc.

The following has been included according to suggestions. “Transmission from asymptomatic pregnant patients’ needs to be characterized in larger population cohorts and symptom assessment needs to be standardized”

- In the introduction around line 58 when referring that pregnant women are not at increased risk of the disease, it is interesting to state that, regardless initial reports affirming that, near misses and maternal deaths with COVID-19 have been reported in several countries worldwide, including Brazil (Takemoto et al 2020) and Mexico (Lumbreras et al 2020) in the LAC region. Additionally, reports from the US CDC (Ellington et al 2020) and Sweden health authority (Collin et al 2020) observed an increased risk of ICU admission and mechanical ventilation in pregnant vs non-pregnant women;

It has been modified according to suggestion, as follows : “While initial evidence suggests that pregnant women were not at increased risk for COVID-19, neither developed a more severe disease compared to non-pregnant adults,(3,4) recent reports suggest increased rates of preterm birth, [5] pneumonia and intensive care unit admission, [6] and maternal mortality, [6,7]

- Figure 1 is remarkably interesting, but the image definition in the version I received is poor. I also believe that there is some repetition of data in both this Figure and Table 2. Maybe figure would be sufficient given that you include the absolute numbers with the corresponding percentages, being an easier way to visualize the information;

According to the reviewer suggestion, Figure 1 quality has been improved and Table 2 has been deleted.

- In Results, it would be better if you include both n and percentages (ex line 149);

According to the reviewer suggestion, it has been corrected across the manuscript.

- Line 189 and Table 4: In my opinion, Apgar scores should be presented as dichotomous variable outcome (not means), or medians with IQR. Mean Apgar score is not something really useful for readers, for example if you have one Apgar 1 and one Apgar 10, the mean would be 5. What does this actually mean?

According to the reviewer suggestion. Mean Apgar scores have been deleted and data is now presented only as dichotomous variables.

Reviewer #3:

- “Nonetheless, available evidence suggests that pregnant women are not at increased risk for COVID-19, neither develop a more severe disease compared to non-pregnant adults.(3,4)” This statement appears too strong and the data reported in the literature are conflicting. This statement could lead the reader of this article to underestimate the impact of COVID-19 in pregnancy. Please consider expanding this point on the basis of works that also suggest a negative impact on pregnancy compared to the general population.

Please see response to Reviewer 2 #4.

- “During the same period of time, national and regional incidence rate showed similar trends.” Please add a reference on this important issue and report here the cumulative prevalence in the general population in the same period (I read that this data is reported in discussion section, but it would be useful to report it here too, furthermore is referred only to the city of Santiago).

The cited text corresponds to an introduction and explanation to the following sentence in the manuscript. It has been corrected by clarifying at the end of the presentation or our analysis. Figure 1 is constructed with data of the National Ministry of Health, previously cited on the text. For better understanding it now reads as follows: “When we compared the daily positivity rate observed in our study group with the daily-incidence rate reported in Santiago, there was a statistical significant positive correlation between them (rho: 0.559, p-value < 0.001)(Figure 1), meaning that during the same period of time, regional incidence rate showed similar trends”

- Please, in the method section, you should report which symptoms were considered suggestive for SARS-CoV-2. The different symptoms should be reported as a percentage in the results.

All of the symptoms suggestive of SARS CoV-2 are presented on the S1 Appendix as targeted anamnesis was made with that survey. We added a S1 Figure where symptom frequencies are shown.

- Although the numbers of positive pregnant women are relatively low, is it possible to have comparison between the asymptomatic and the symptomatic about the maternal and the fetal outcomes? Maybe it can be presented as supplementary material with a short comment in the main text.

According to the reviewer suggestion, requested analysis has been added as supplementary material S2 Appendix. “Table 3 summarize main perinatal outcomes and S2 Appendix compares results among symptomatic and asymptomatic cases.”

- The data of the work by Sutton et al are rightly reported in your paper, but the discussion should be enriched considering similar works from other geographic realities, for example consider these for a comparison with your experience:

Discussion has been extended in order to consider other reports. Please see response to Reviewer 2 #2.

- Clarify that universal screening should be performed only in endemic areas. In places where the coronavirus is not endemic it would be just a waste of resources.

Changes have been made according to suggestion. It now reads as follows “It appears that universal screening, at least in endemic areas, in unselected obstetrical population at delivery may provide good estimates of population-level prevalence of SARS CoV-2 infection, and better management of the obstetrical population, with protection of health team, proper patient isolation, prompt neonatal testing and targeted follow-up.”

- The references do not follow the instructions of the authors. Please correct them.

They have been corrected according to requirements.

Submitted filename: Response to reviewers.docx

Click here for additional data file.

7 Sep 2020

PONE-D-20-20646R1

Routine screening for SARS CoV-2 in unselected pregnant women at delivery.

PLOS ONE

Dear Dr. Caradeux,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

SPECIFIC ACADEMIC EDITOR COMMENTS: There are still some comments from one of the reviewers. The discussion still needs to be strengthened with inclusion of all relevant citations. Please address ALL comments in your revised manuscript.

Please submit your revised manuscript by Oct 22 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Frank T. Spradley

Academic Editor

PLOS ONE

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

Reviewer #2: (No Response)

Reviewer #3: Most of this referee's requests have been considered.

However, the discussion still appears too weak.

If the final message of the authors is to propose a universal screening for SARS-CoV-2 in pregnancy in ednemic area, it is essential to compare in depth with other epidemiological realities as already suggested.

Moreover manuscripts reported in my previous review with important epidemiological data have not been considered in this revised paper (DOI: 10.1016/j.ajogmf.2020.100118, DOI: 10.1002/jmv.26267, DOI: 10.1002/ijgo.13162), but again, if the aim is to propose a universal screening for COVID-19 in pregnancy, I believe it is essential to mention and discuss them in order to provide readers of this paper a better idea of the global picture on the pandemic in pregnancy

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (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. Registration is free. 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 PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

10 Sep 2020

Dear Editor, please find below and itemized answers to all the reviewers queries according to journal requested format.

Reviewer #3: Most of this referee's requests have been considered. However, the discussion still appears too weak. If the final message of the authors is to propose a universal screening for SARS-CoV-2 in pregnancy in endemic area, it is essential to compare in depth with other epidemiological realities as already suggested. Moreover manuscripts reported in my previous review with important epidemiological data have not been considered in this revised paper (DOI: 10.1016/j.ajogmf.2020.100118, DOI: 10.1002/jmv.26267, DOI:10.1002/ijgo.13162), but again, if the aim is to propose a universal screening for COVID-19 in pregnancy, I believe it is essential to mention and discuss them in order to provide readers of this paper a better idea of the global picture on the pandemic in pregnancy.

Reviewer suggestion has been considered and changes have been made according to recommendations across the manuscript in order to strengthen our arguments and emphasize the role of universal screening among obstetric population. Regarding comparison to previous reports it’s our believe that a full “in dept” analysis of pandemic situation between different geographic areas is beyond the scope of our study as several complex factors should be taken into account to proper comparison, such as social dynamics, population healthcare access or government policies. It’s true that some of the recommended references by the reviewer (Cosma S, et al.) compare different realities thought accumulative incidence, however the former is this directly affected by testing number. Nonetheless, in order to allow the reader a better interpretation of reported results the following paragraph has been added into the discussion section:

“It could be argued that previous reports on universal screening in obstetrics population do not provide information on the local situation of the pandemic, so it is difficult to estimate the real implications and external validity of their findings. Moreover, as it has been stated, the different time points of patient recruitment along with the rising and falling phase of the pandemic curve, explain the different rates of positive RT‐PCR results.[22] Therefore, in areas with high prevalence of infection, it could be expected that more women may be positive but asymptomatic.[23] This could be seen in reports by Sutton et al.[10], Vintzileos et al.[9], Bianco et al.[13] and Dória et al.[16] All of them were conducted in areas and timepoints with reported high prevalence of infection,[24] and showed higher observed SARS-CoV-2 infection prevalence, ranging between 11 and 19%, with up to 15% of asymptomatic confirmed cases among screened population. On the other side, reports by Naqvi et al.[25] and Gagliardi et al.[12], reported a low performance of universal screening based either on an overall lower disease burden in their region or due to a referred “steady state” of virus circulation, with less than 1% of asymptomatic confirmed cases. In an intermediate epidemiological situation reports by Khalil et al.[11], Miller et al.[14] and Ochiai et al.[26] presented observed SARS-CoV-2 infection prevalence ranging between 3 and 7%, with up to 6% of asymptomatic confirmed cases among screened population, which are similar to our findings.”

Submitted filename: Response to reviewers 2.docx

Click here for additional data file.

16 Sep 2020

Routine screening for SARS CoV-2 in unselected pregnant women at delivery.

PONE-D-20-20646R2

Dear Dr. Caradeux,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Frank T. Spradley

Academic Editor

PLOS ONE

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #3: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #3: No

21 Sep 2020

PONE-D-20-20646R2

Routine screening for SARS CoV-2 in unselected pregnant women at delivery.

Dear Dr. Caradeux:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Frank T. Spradley

Academic Editor

PLOS ONE