Abstract
Objective
To evaluate if peri-pregnancy timing of a PCR+ test for SARS-CoV-2 RNA affects pregnancy outcomes and placental pathology.
Methods
This is a retrospective cohort study conducted in a tertiary center. Pregnancy outcomes and placental pathology were compiled for women who tested positive for SARS-CoV-2 RNA from a nasopharyngeal swab assessed by RT-PCR. The population comprised four groups that were PCR+ preconception (T0) or in the 1st (T1), 2nd (T2), or 3rd (T3) trimester of pregnancy. A fifth, control group (TC) tested PCR- for SARS-CoV-2 before delivery.
Results
Seventy-one pregnancies were studied. The T0 group exhibited lower gestational ages at delivery, had infants with the lowest birth weights, the highest rate of pregnancy loss before 20 weeks. Features of maternal vascular malperfusion and accelerated villous maturation were prominent findings in the histopathology of placentas from women PCR+ for SARS-CoV-2 RNA, especially in the T0 and the T1 groups.
Conclusion
Women at highest risk for pregnancy complications are those who test PCR+ for viral RNA preconception or during first trimester of pregnancy.
Keywords: SARS-CoV-2, Timing, COVID-19, Placental pathology, Pregnancy outcome, Neonatal outcome
1. Introduction
The data support pregnancy as a risk factor for severe disease associated with COVID-19 [1], [2], [3]. SARS-CoV-2 infection during pregnancy associates with numerous adverse pregnancy outcomes, including preeclampsia, preterm birth, and stillbirth, especially among pregnant women with clinically severe COVID-19 disease [2].
As an organ unique to pregnancy, the placenta is pivotal to pregnancy outcomes. A simplified view of the human chorioallantoic placental structure reveals two autonomous circulations interfaced by trophoblast on the connective tissue surface of villi. The two circulations are discreet and normally do not mix. The maternal circulation flows through arteriole blood vessels in the uterine bed, traverses the placental intervillous space, and exits via endometrial veins. The fetal circulation includes ramifying villous blood vessels that merge into vessels on the chorionic plate to connect to the umbilical cord and to provide circulation to the fetal body. Histopathological abnormalities in blood vessels, intervillous space, or villi can lead to characteristic microscopic features. For example, maternal hypertensive disorders commonly yield small placentas and microscopic features related to abnormal remodeling of decidual arterioles in the basal plate and superficial implantation, termed maternal vascular malperfusion (MVM). This histopathology may be localized or global within the placental disc, and may include infarct, accelerated villous maturation (AVM), distal villous hypoplasia and decidual arteriopathy. Umbilical cord disorders can also produce abnormalities in the fetal circulation (fetal vascular malperfusion, FVM), such as fetal vessel thrombosis, avascular villi, and villous stromal karyorrhexis [4]. The pathology may evolve with multiple lesions, interacting with each other to affect downstream organ function.
A review of 56 studies reporting on placental pathology of pregnant women with SARS-CoV-2 infection showed that the percentage of placental examinations with histopathologic findings of MVM (30.7 %), FVM (27.1 %), and acute (22.7 %) and chronic inflammation (25.7 %), was higher than expected [5]. However, our prior study of COVID-19 related placental pathology included a control population and demonstrated that placentas from women who were PCR+ for SARS-CoV-2 during the 3rd trimester did not show differences in histopathology compared with gestational age matched PCR- controls [6].
Whether the timing of maternal SARS-CoV-2 infection relative to conception influences pregnancy outcome or placental histopathology is debated [7].The above discrepancy among results raised the specific question of whether or not the timing in gestation a patient becomes SARS-CoV-2 PCR+ influences the pathology of the placenta at delivery [8]. Indeed, Glynn et al. reported that infection by SARS-CoV-2 < 14 days from delivery, designated acute onset infection, exhibited FVM lesions prominently. We tested the hypothesis that the time peri-pregnancy when a woman tests SARS-CoV-2 PCR+ influences pregnancy outcomes and placental pathology. We specifically question whether or not a positive PCR for SARS-CoV-2 during the 1st trimester leads to worse pregnancy outcomes, more severe placental pathology, or both compared to infections later in gestation.
2. Methods
2.1. Institution review board approval
This study was approved under IRB ID# 201902092 by the institutional Office of Institution Review Board.
2.2. Study design
We conducted a retrospective cohort study between April 2020 and September 2021. Maternal SARS-CoV-2 PCR results were identified from the laboratory information system. We retrieved the corresponding obstetrical and newborn data and the written pathology reports, and original specimens from placenta or products of conception, for further analysis.
2.3. Study population
Patients were universally tested on admission to labor and delivery and were tested for cause (for example, if they had respiratory symptoms) at other times. In general patients were tested once before labor and delivery. Patients' chart was also reviewed for SARS-CoV-2 PCR testing. Patients were assigned to a trimester for onset of infection based on the time of their 1st positive PCR test. Patients testing PCR+ for SARS-CoV-2 were classified into four groups: pre-conception during the study period (T0), in the 1st (T1), 2nd (T2), or 3rd (T3) trimester of pregnancy. A fifth group (TC) served as control pregnancies, who tested negative by PCR and delivered a singleton newborn in the 3rd trimester and had a placenta pathology evaluation due to comorbidities or for any other reason. For the T0 group, based on gestational age obtained by obstetric ultrasonography, we estimated the difference between the COVID-19 testing date and the conception date. The current study was an expansion of a prior study, by adding more patients with PCR+ for SARS-CoV-2 before and during 1st or 2nd trimesters of pregnancy [7].
2.4. Submission criteria and methodology for placental examination
Placentas were submitted to pathology following established guidelines [7] for evaluation of maternal or fetal conditions or gross abnormalities of the placenta [8]. Notably, a maternal positive SARS-CoV-2 test was included as an indication for placental submission. All placentas from the pregnant woman who tested positive for SARS-CoV-2 were expected to be submitted for pathological examination. Placental reports were composed by pathologists who were board certified in Anatomical and Gynecological Pathology fellowship training, or board certified in both Anatomical and Pediatric Pathology. Slides stained with hematoxylin and eosin (H&E) in selected cases, where the pathology report was unclear, were centrally reviewed, and a final disposition made by a board-certified pediatric pathologist (MH) blinded to clinical history, as previously described [6].
Gross and microscopic features were extracted from the pathology reports, including the following: placental trimmed weight, placental weight percentile, cord insertion, features of MVM including infarcts, retroplacental hemorrhage, distal villous hypoplasia, AVM and decidual arteriopathy, features of FVM, including thrombosis, avascular villi, intramural fibrin deposition, villous stromal-vascular karyorrhexis, chorangiosis, delayed villous maturation, villous edema, perivillous fibrin type fibrinoid deposition, acute and chronic inflammation, as recommended5. Placental weight percentile for gestational age was determined based on a published chart [9]. For acute inflammation, we sub-categorized into maternal inflammatory response, represented by acute chorioamnionitis, and fetal inflammatory response, represented by acute vasculitis of umbilical cord, chorionic plate blood vessels, and acute funisitis of the umbilical cord. For chronic inflammation, we sub-categorized into villitis of unknown etiology, chronic chorioamnionitis and chronic (lymphoplasmacytic) deciduitis. We specifically searched for features of SARS-CoV-2 placentitis [10], including the triad of histiocytic intervillositis, increased perivillous fibrin, and villous trophoblastic necrosis.
2.5. Clinical information
Maternal age, obstetric history, respiratory symptoms, maternal comorbidities, including history of hypertension and diabetes before or during gestation, cardiomyopathy, uterine malformations, gestational age (GA) of SARS-CoV-2 PCR testing, GA at delivery, birth weight, one- and five-minute APGAR scores, and COVID-19 vaccination history were extracted from the electronic medical records. Severity of COVID-19 was classified based on clinical spectrum of SARS-CoV-2 from National Institute of Health (NIH) as asymptomatic, if the individual tested positive without any symptom consistent with COVID-19; mild, if the individual presented with fever, cough, sore throat, malaise, headache, muscle pain, nausea, vomiting, diarrhea, loss of taste or smell without shortness of breath or need for hospital admission; moderate, if the individual showed lower respiratory tract disease with dyspnea or need for oxygen supplementation by nasal cannula; and severe, if the individual needed mechanical ventilation or was admitted to the intensive care unit due to COVID-19 [11].
Adverse pregnancy and neonatal outcomes included preterm birth if before 37 weeks' GA, preeclampsia, intrauterine fetal demise (IUFD), neonatal death, and neonatal intensive care unit (NICU) admission.
2.6. SARS-CoV-2 testing
Testing for pregnant women via nasopharyngeal swabs was performed at the Molecular Infectious Disease Laboratory of Barnes-Jewish Hospital. The 2019-Novel Coronavirus Assay (COVID-19) real-time polymerase chain reaction (RT-PCR) assay was used to detect the presence of SARS-CoV-2 RNA.
2.7. Statistical analysis
The Shapiro–Wilks test was used to check normality of the distribution of continuous outcome variables. For normal distributed data, the mean and standard deviation and comparisons among groups were carried out using one-way ANOVA. For non-parametric values, median and interquartile range was obtained, and groups were compared by Kruskal-Wallis. If significant, post-hoc pairwise comparison was conducted using Tukey's Studentized Range test or Dunn's Test if appropriate. Chi-square or Fisher's exact test was used for categorical variables. Significance was set as P < 0.05. All statistical tests were performed with SAS 9.4 (SAS Inc., Cary, NC) and R programming version 4.1.2 (Vienna, Austria).
3. Results
3.1. Demographic features
Seventy-one pregnancies were studied, including 19 that were PCR- in the 3rd trimester (TC) and 52 that were maternal SARS-CoV-2 PCR+. Maternal age, comorbidities, and mode of delivery did not differ significantly among the groups (Table 1 ). Among patients testing positive, 11 were in the T0 group, 8 were in the T1 group, 16 were in the T2, and 17 were in the T3. T0 group ranged from 12 to 399 days, with a median of 97 days and an inter-quartile ratio of IQR 32–222 days.
Table 1.
Maternal demographics, pregnancy, and neonatal outcomes (T0 = COVID-19 before pregnancy; T1 = COVID-19 during 1st of gestation; T2 = 2nd of gestation; T3 = 3rd of gestation; TC = no COVID). For comorbidities, preeclampsia, cesarean delivery, preterm birth, stillborn, NICU admission, APGAR and birth weight analysis, we exclude patients who had a pregnancy loss <20 weeks.
| Features | T0 (N = 11) | T1 (N = 8) | T2 (N = 16) | T3 (N = 17) | TC (N = 19) | P-value |
|---|---|---|---|---|---|---|
| Mean maternal age in years (range) | 30.8 ± 4.7 (25–39) | 27.1 ± 5.1 (19–34) | 30.8 ± 5.9 (20–39) | 26.1 ± 7.2 (15–37) | 26.9 ± 5.9 (18–37) | 0.11 |
| Comorbidities | 4/7 (26.3 %) | 3/8 (37.5 %) | 5/16 (31.3 %) | 1/17 (5.9 %) | 5/14 (26.3 %) | 0.28 |
| Preeclampsia | 2/7 (28.6 %) | 4/8 (50 %) | 4/16 (25 %) | 0/17 (0.0 %) | 4/19 (21.1 %) | 0.06 |
| Pregnancy loss before 20 weeks | 4/11 (36.4 %) | 0/8 (0.0 %) | 0/16 (0.0 %) | 0/17 (0.0 %) | 0/19 (0.0 %) | <0.01 |
| Cesarean deliverya | 2/7 (28.6 %) | 3/8 (37.5 %) | 10/16 (65.5 %) | 7/17 (41.18 %) | 4/15 (21.1 %) | 0.10 |
| Preterm birtha | 5/7 (71.3 %) | 4/8 (50 %) | 4/16 (25 %) | 7/17 (23.5 %) | 3/19 (15.8 %) | 0.05 |
| Stillborna | 0/7 | 0/8 | 0/16 | 0/17 | 0/19 | N/A |
| Neonatal deatha | 2/7 (28.6 %) | 0/8 (0 %) | 0/16 (0 %) | 1/17 (5.9 %) | 0/19 (0 %) | 0.02 |
| NICU admissiona | 2/7 (28.6 %) | 2/8 (25.0 %) | 3/16 (18.8 %) | 4/17 (23.5 %) | 7/18 (38.9 %) | 0.11 |
| Median APGAR 1 min (range)a | 8.0 (6.0–8.0) | 8.0 (6.0–8.0) | 8.0 (3.0–9.0) | 9.0 (1.0–8.0) | 8.0 (3.0–8.0) | 0.46 |
| Median APGAR 5 min (range)a | 8.0 (5.0–9.0) | 9.0 (8.0–9.0) | 9.0 (8.0–9.0) | 9.0 (2.0–9.0) | 9.0 (7.0–9.0) | 0.19 |
| Mean birth weight in g (range)a | 2011.4 ± 979.9 (660.0–3150.0) | 2595.0 ± 291.3 (2160.0–3040.0) | 3012.0 ± 744.1 (1990.0–4706.0) | 2904.7 ± 472.1 (2180–3710) | 2839.44 ± 728.9 (1370.0–3980.0) | 0.02 |
Excluding cases with pregnancy loss <20 weeks.
All patients in the T1 and 91 % in the T0 group presented the mild form of COVID-19 infection, with none presenting the moderate or severe form. Conversely, 62 % and 35 % of patients in T2 and T3 groups, respectively, presented the mild form of COVID-19 (Table 2 ).
Table 2.
Distribution and comparison of COVID-19 infection severity among the participants.
| Severity | T0 (N = 11) | T1 (N = 8) | T2 (N = 16) | T3 (N = 17) | TC (N = 19) | P-value |
|---|---|---|---|---|---|---|
| Asymptomatic | 1/11 (9.09 %) | 0/8 (0 %) | 2/16 (12.50 %) | 8/17 (47.06 %) | N/A | 0.03⁎ |
| Mild | 10/11 (90.91 %) | 8/8 (100 %) | 10/16 (62.50 %) | 6/17 (35.29 %) | N/A | |
| Moderate | 0/11 (0 %) | 8/8 (0 %) | 3/16 (18.75 %) | 2/17 (11.76 %) | N/A | |
| Severe | 0/11 (0 %) | 0/8 (0 %) | 0/16 (0 %) | 1/17 (5.88 %) | N/A | |
| Missing data | 0/11 (0 %) | 0/8 (0 %) | 1/16 (6.25 %) | 0/17 (0 %) | 19/19 (100 %) |
P-value was calculated excluding Tc.
3.2. Pregnancy outcomes
Pregnancy loss before 20 weeks was seen only in the T0 group who tested PCR+ before conception. Preterm labor was more often seen in the T0 group, but the trend was at the borderline for statistical significance (P = 0.05; Table 1). Importantly, GA at delivery in T0 patients was remarkably lower when compared to all other groups (Fig. 1A). Among all PCR+ groups progressing to delivery, there was a significant difference (P = 0.01) in preterm birth rates. Infection in the T1 group associated with a non-significant (P = 0.06) higher incidence of preeclampsia, and preeclampsia frequencies were similar among all other groups (Table 1). Furthermore, no statistical differences were seen regarding cesarean delivery rate among the participants. None of the pregnancies resulted in stillbirth.
Fig. 1.
A: Distribution and comparison of gestational ages at delivery among groups – T0, T1, T2, T3, and TC (P = 0.01). Significance difference seen due to comparison of T0 with remaining groups. B: Differences in birth weight among groups, P < 0.01 (T0 = COVID-19 before pregnancy; T1 = COVID-19 during 1st of gestation; T2 = 2nd of gestation; T3 = 3rd of gestation; TC = no COVID). Significance difference seen due to comparison of T0 with remaining groups.
3.3. Neonatal outcomes
Birth weight at delivery was lowest in T0 patients (2100 g mean birthweight) who were infected preconception, compared to TC controls (2900 g mean birthweight), followed by T1 patients infected during the first trimester of gestation (P < 0.01; Figs. 1B). Two of seven (28.6 %) T0 patients who were infected by SARS-CoV-2 preconception had a neonatal demise, but only one of 17 patients (5.9 %) who developed a SARS-CoV-2 PCR+ test during the third trimester of gestation (T3) had babies who died in the neonatal period (P = 0.02). No neonatal demises occurred in the T1, T2, or TC patient groups. APGAR scores at one- and five- minutes and neonatal intensive care admissions were no different among the groups (Table 1).
3.4. Placental histology
No significant differences were observed for placental weights, birth weights or fetoplacental weight ratios, percentage of small-for-gestational age placentas defined as placental weight < 10th percentile),or large-for-gestational age defined as placental weight > 90th percentile. Among all patients with PCR+ at any time in the peri-pregnancy period, 63.0 % of placentas demonstrated features of MVM and 44.7 % showed AVM. Moreover, >70 % of placentas in the T0, T1, and T2 groups had features of MVM, significantly higher than the T3 and TC groups. The T0 and T1 groups also had the highest frequency of AVM in their placentas, while TC patients who were PCR- for SARS-CoV-2 presented the lowest incidence (P < 0.01) of this histopathology (Table 3 , Fig. 2 ).
Table 3.
Histopathological features of placentas (T0 = COVID-19 before pregnancy; T1 = COVID-19 during 1st of gestation; T2 = 2nd of gestation; T3 = 3rd of gestation; TC = no COVID).
| Histologic feature | All groups infected | T0 (N = 7) | T1 (N = 8) | T2 (N = 16) | T3 (N = 17) | TC (N = 19) | P-value |
|---|---|---|---|---|---|---|---|
| Mean placental weight in g (range) | 330.0 ± 152.4 (149.0–550.0) | 404.1 ± 85.9 (264.0–537.0) | 467.6 ± 123.6 (246.0–699.0) | 451.5 ± 75.4 (337.5–577.0) | 434.5 ± 106.6 (255.4–632.8) | 0.09 | |
| Small-for-gestational age placenta | 3 | 6 | 10 | 11 | 11 | 0.74 | |
| Large-for-gestational age placenta | 0 | 0 | 1 | 0 | 0 | 0.45 | |
| Mean birth weight: Placental weight ratio (range) | 5.8 ± 1.5 3.8–8.5 |
6.8 ± 2.1 4.0–10.6 |
6.6 ± 1.3 3.1–9.4 |
6.5 ± 0.9 5.2–8.3 |
6.6 ± 1.1 4.2–8.6 |
0.70 | |
| Maternal vascular mal perfusion | 29/46 (63.0 %)a | 5/7 (71.4 %) | 5/7 (71.4 %) | 11/15 (73.3 %)b | 8/17 (47.1 %) | 6/19 (31.6 %) | 0.03 |
| Accelerated villous maturation | 21/47 (44.7 %)a | 5/7 (71.4 %)b | 5/7 (71.4 %)b | 6/15 (37.5 %) | 3/17 (17.6 %) | 2/19 (10.5 %) | <0.01 |
| Fetal vascular mal perfusion | 8/45 (17.8 %) | 1/7 (14.3 %) | 1/6 (16.6 %) | 1/15 (6.7 %) | 6/17 (35.3 %) | 7/19 (36.8 %) | 0.12 |
| Maternal inflammatory response | 4/45 (8.9 %) | 1/7 (14.3 %) | 1/7 (14.3 %) | 0/15 (0.0 %) | 2/17 (11.7 %) | 3/19 (15.8 %) | 0.11 |
| Fetal inflammatory response | 4/45 (8.9 %) | 2/7 (11.7 %) | 0/7 (0.0 %) | 0/15 (0.0 %) | 2/17 (11.7 %) | 4/19 (21.1 %) | 0.18 |
| Chronic inflammation | 4/45 (8.9 %) | 1/7 (14.3 %) | 2/7 (11.8 %) | 1/15 (6.7 %) | 0/17 (0 %) | 2/19 (10.5 %) | 0.26 |
Comparison between T+ vs Tc.
Comparison between T3 vs Tc.
Fig. 2.
Typical histopathology of placentas from patients who tested PCR+ for SARS-CoV-2 RNA. A: Villous morphology of a placenta at 32 weeks GA, appearing unusually similar to villi of a term placenta, with numerous small diameter or hyper mature villi. H&E, 40×. B: Avascular villi from a placenta delivered at 39 weeks' GA from a patient PCR+ for SARS-CoV-2 RNA. There are normal villi with fetal villous blood vessels apparent in the upper field, but the central portion shows chorionic villi with loss of fetal villous capillaries and deposits of hyaline fibrosis. H&E, 200×. C: Acute chorioamnionitis with numerous neutrophils distributed from the sub chorionic intervillous space (bottom) to the amniocyte covering the chorionic plate (top). H&E, 100×. D: High grade villitis of unknown etiology, with inflammatory cells colonizing more than ten adjacent villi. H&E, 200×. E: SARS-CoV-2 placentitis showing the triad of histiocytic inter-villositis, intervillous fibrin deposition and trophoblastic necrosis. H&E, 100×. F: Image of SARS-CoV-2 placentitis after specimen immunostaining for CD68 as a histiocyte, macrophage marker. The field shows the triad listed in E, with intervillous space cells immune-stained for CD68. 100×.
Features of FVM were not significantly different among the PCR+ and PCR- groups. Importantly, there were no differences in the histological features of inflammation among the placentas, including maternal acute inflammatory response, fetal acute inflammatory response, and chronic inflammation (Table 3). None of the PCR+ groups nor the control group exhibited chronic histiocytic intervillositis (Fig. 2E and F). There were no other group differences in the histopathology.
4. Discussion
To our best knowledge, this is the first article that found different pregnancy and pathology outcomes according to the timing of SARS-CoV-2 infection. The data support our hypothesis that the time peri-pregnancy when a woman tests SARS-CoV-2 PCR+ influences both pregnancy outcomes and placental pathology. We found that T0 patients who were infected by SARS-CoV-2 before the pregnancy delivered at the lowest GA, had infants with the lowest birth weight, had the most pregnancy losses before 20 weeks, and experienced some neonatal deaths, compared to other groups. Moreover, T1 patients with COVID-19 during the 1st trimester of pregnancy had a higher incidence of preterm labor, when compared to the other groups. There was a high frequency of MVM and AVM in the placental pathology of PCR+ patients, especially in T0 and T1 patients, respectively, compared to the other groups.
Pregnancy generally worsens COVID-19 outcomes [2], but how timing of infection during pregnancy influences outcomes is poorly understood [1], [2], [3], [12]. Indeed, while there are >50 studies of placental pathology in delivered patients, only four cases of miscarriage and one neonatal death were reported among 324 pregnancies compiled from 24 of the studies [12]. Pathological examination in gonadal and uterine tissues of COVID-19 infected patients is limited [13] and the ability to relate timing of infection and pregnancy GA has not previously been done. Collectively, the data indicate that patients testing PCR+ for SARS CoV-2 RNA in preconception and in early pregnancy are at high risk for sub-optimal pregnancy outcome and should receive antenatal surveillance tuned to the high risk for adverse obstetrical outcomes.
4.1. COVID-19 and pregnancy outcome, and potential mechanisms
The mechanisms involved in poor pregnancy outcomes in pregnancies infected early with SARS-CoV-2 virus remain speculative at this point in the pandemic. They include different expression of ACE2 at different time of pregnancy including preconception, virus related chronic inflammation, chronic presence of virus in uterine bed or abnormal angiogenesis of local uterine/placental microenvironment. The “long COVID” is a condition attracting more and more attention, with a broad spectrum of subacute and/or chronic symptoms and signs that follow the acute phase of SARS-CoV-2 infection [14]. Pathophysiology, prevalence, or during of “long COVID” are all not known. We speculate that it would be interesting to see if the more adverse outcome associated with preconception SARS-CoV-2 infection part of this “long COVID”, which seems to be independent of the severity of the acute SARS-CoV-2 infection. Unfortunately, we do not have enough data to analyze “long COVID” in our study population. Interestingly, none of patients who had COVID-19 before pregnancy and at early pregnancy presented moderate or severe symptoms, in contrast to those who had COVID-19 during 2nd and 3rd trimester, despite our findings of worse gestational outcomes seen in the T0 and T1 groups.
Angiotensin converting enzyme 2 (ACE2), which is the entry point receptor of SARS-CoV-2 into human cells, is expressed in a wide array of cells in human placenta and there is an increased expression of ACE2 from the early to mid-secretory phases to early pregnancy [15], [16], [17]. This pattern of expression implies an increase in ACE2 during the implantation [18], suggesting abundant receptors are available peri-implantation for SARS-CoV-2 to bind, establish infection, and influence the development of the decidua, trophectoderm, and chorioallantoic placenta at the beginning of pregnancy. This observation suggests one potential mechanism by which the poorest gestational outcomes are seen in women testing PCR+ for SARS-CoV-2 viral RNA preconception and in the 1st trimester of pregnancy. The effects on development could continue well beyond the time viral shedding ceases. TMPRSS2 is a serine protease that increases protein priming to increase infectivity for SARS-CoV-2 infection [13], [19], [20]. The presence of SARS-CoV-2 is highest in maternal decidua, increases angiotensin II receptor type 1 (AT1R), and increases soluble fms-like tyrosine kinase-1 (sFlt-1; also known as VEGF-1 receptor). Thus, we consider that preconception or early gestational infections by SARS-CoV-2 may result in an increased burden of virus in local utero-placental vasculature, predisposing to endothelial injury, microthrombi, and local ischemia.
4.2. SARS-CoV-2 infection, maternal vascular malperfusion and accelerated villous maturation
We discovered a high incidence of the histopathology for MVM and AVM in placentas of PCR+ women [20]. MVM reflects the structural changes induced by an impaired maternal blood supply to the feto-placental unit. MVM is characteristic of hypertensive disorders in pregnancy, which are well known to derive from superficial implantation, failed remodeling of maternal uterine spiral arterioles, and increased maternal levels of the antiangiogenic mediator sFlt-1. MVM associates with higher-than-expected SGA newborns in pregnancies with hypertensive disorders, and a higher incidence of MVM in the pregnancies testing PCR+ may partly explain the disproportionately low birthweights delivered among the group testing positive for SARS-CoV-2. Notably, preeclampsia was not more common in PCR+ vs. PCR- pregnancies in our study. We speculate there was an adequate balance of angiogenic/antiangiogenic mediators, or lack of maternal susceptibility to any imbalances, in women infected with SARS-CoV-2.
4.3. Strengths and limitations of our study
The strengths of our study are the correlation of SARS-CoV-2 PCR+ test results preconception, and at each trimester, with maternal and neonatal outcomes. All groups were similar for maternal age, comorbidities, and rate of Cesarean delivery. Moreover, the detailed analyses of the placentas were conducted by board certified pathologists. A final strength of the study was collection of vaccination status. We believe the fact that only five patients were vaccinated, spread among the groups, effectively eliminates vaccination status as a confounding independent variable in the results.
Limitations of our study include the retrospective design, single center analysis of patients and small sample size. Lack of placental tissue testing by RT-PCR or immunohistochemistry was another limitation but this could be a direction for future studies. The fact that the control group was tested close to the delivery date is a limitation of the study. We limited bias as best we could by conducting blinded analyses of clinical data extracted, pathology reports, and specimen slides reviewed. We do not have an extensive list of all possible comorbidities. Additionally, some groups had a small sample size, making a beta statistical error more likely in our results. Finally, the PCR-control group without infection by SARS-CoV-2 was tested close to their delivery date and not throughout gestation. This approach was pragmatic yet has the potential to miss an asymptomatic patient with a PCR+ result earlier in gestation. At this point, no serologic assays have been proven to efficiently identify previous exposure by SARS-CoV-2, since they do not capture cellular-mediated immunity and the duration of humoral response is unclear [21].
In conclusion, our single institution experience confirms our hypothesis that the time peri-pregnancy when a woman tests PCR+ for SARS-CoV-2 RNA influences clinical outcomes and placental pathology. Importantly, mothers testing PCR+ for SARS-CoV-2 RNA preconception, or during early gestation, are at most risk for adverse clinical outcomes and placental pathology. This finding is important to consider in public health approaches to limit adverse effects of COVID for patients desiring pregnancy, not only during the pandemic but also, for those who may delay childbearing and yet already be at higher risk from having a previous SARS-CoV-2 infection.
Declaration of competing interest
All co-authors declare no conflict of interest. This study was supported by faculty developmental fund to Dr. Mai He by the Department of Pathology & Immunology, Washington University in St. Louis School of Medicine.
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