Analysis of complement deposition and viral RNA in placentas of COVID-19 patients

Maternal COVID-19 exposure and placental characteristics

INTRODUCTION

The impact of COVID-19 on the placenta is poorly described, particularly among minority women.

MATERIALS AND METHODS

This is a retrospective case-control study. Micro- and macroscopic placental pathologic findings were compared for 15 COVID-19 positive and 36 negative mothers. Cases and controls were frequency matched on gestational age, race, maternal comorbidities, and delivery type. Data from the electronic medical record were supplemented with independent review of microscopic slides.

RESULTS

Placentas from cases and controls were similar except the median distance from the site of the cord insertion to the nearest disk margin was statistically significantly shorter among placentas from COVID-19 positive cases (3.5 versus 6.0 cm, p = 0.006). Case status was not associated with an increased risk of placental pathologies.

CONCLUSION

There are few pathologic differences between placentas of COVID-19 positive and negative mothers. Additional studies are needed to investigate the role of timing of infection.

Extracellular vesicles alter trophoblast function in pregnancies complicated by COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and resulting coronavirus disease (COVID-19) causes placental dysfunction, which increases the risk of adverse pregnancy outcomes. While abnormal placental pathology resulting from COVID-19 is common, direct infection of the placenta is rare. This suggests that pathophysiology associated with maternal COVID-19, rather than direct placental infection, is responsible for placental dysfunction and alteration of the placental transcriptome. We hypothesized that maternal circulating extracellular vesicles (EVs), altered by COVID-19 during pregnancy, contribute to placental dysfunction. To examine this hypothesis, we characterized maternal circulating EVs from pregnancies complicated by COVID-19 and tested their effects on trophoblast cell physiology in vitro . We found that the gestational timing of COVID-19 is a major determinant of circulating EV function and cargo. In vitro trophoblast exposure to EVs isolated from patients with an active infection at the time of delivery, but not EVs isolated from Controls, altered key trophoblast functions including hormone production and invasion. Thus, circulating EVs from participants with an active infection, both symptomatic and asymptomatic cases, can disrupt vital trophoblast functions. EV cargo differed between participants with COVID-19 and Controls, which may contribute to the disruption of the placental transcriptome and morphology. Our findings show that COVID-19 can have effects throughout pregnancy on circulating EVs and circulating EVs are likely to participate in placental dysfunction induced by COVID-19.

Diffusion-sensitized magnetic resonance imaging highlights placental microstructural damage in patients with previous SARS-CoV-2 pregnancy infection

INTRODUCTION

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been a major global health problem since December 2019. This work aimed to investigate whether pregnant women's mild and moderate SARS-CoV-2 infection was associated with microstructural and vascular changes in the placenta observable in vivo by Intravoxel Incoherent Motion (IVIM) at different gestational ages (GA).

METHODS

This was a retrospective, nested case-control of pregnant women during the SARS-CoV-2 pandemic (COVID-19 group, n = 14) compared to pre-pandemic healthy controls (n = 19). MRI IVIM protocol at 1.5T was constituted of diffusion-weighted (DW) images with TR/TE = 3100/76 ms and 10 b-values (0,10,30,50,75,100,200,400,700,1000s/mm2). Differences between IVIM parameters D (diffusion), and f (fractional perfusion) quantified in the two groups were evaluated using the ANOVA test with Bonferroni correction and linear correlation between IVIM metrics and GA, COVID-19 duration, the delay time between a positive SARS-CoV-2 test and MRI examination (delay-time exam+) was studied by Pearson-test.

RESULTS

D was significantly higher in the COVID-19 placentas compared to that of the age-matched healthy group (p < 0.04 in fetal and p < 0.007 in maternal site). No significant difference between f values was found in the two groups suggesting no-specific microstructural damage with no perfusion alteration (potentially quantified by f) in mild/moderate SARS-Cov-2 placentas. A significant negative correlation was found between D and GA in the COVID-19 placentas whereas no significant correlation was found in the control placentas reflecting a possible accelerated senescence process due to COVID-19.

DISCUSSION

We report impaired microstructural placental development during pregnancy and the absence of perfusion-IVIM parameter changes that may indicate no perfusion changing through microvessels and microvilli in the placentas of pregnancies with mild/moderate SARS-Cov-2 after reaching negativity.

Clinical Features of SARS-CoV-2 Infection During Pregnancy and Associated Placental Pathologies

SUMMARY

We reviewed the clinicopathologic findings of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-exposed placentas at our institution. We identified patients diagnosed with SARS-CoV-2 during pregnancy (March-October 2020). Clinical data included gestational age at diagnosis and delivery and maternal symptoms. Hematoxylin and eosin slides were reviewed for maternal vascular malperfusion, fetal vascular malperfusion, chronic villitis, amniotic fluid infection, intervillous thrombi, fibrin deposition, and infarction. Immunohistochemistry (IHC) for coronavirus spike protein and RNA in situ hybridization (ISH) for SARS-CoV-2 was performed on a subset of blocks. A review of placentas from age-matched patients received March-October 2019 was conducted as a comparison cohort. A total of 151 patients were identified. Placentas in the 2 groups were similar in weight for gestational age and had similar rates of maternal vascular malperfusion, fetal vascular malperfusion, amniotic fluid infection, intervillous thrombi, fibrin deposition, and infarction. Chronic villitis was the only significantly different pathologic finding between cases and controls (29% of cases showed chronic villitis vs. 8% of controls, P <0.001). Overall, 146/151 (96.7%) cases were negative for IHC and 129/133 (97%) cases were negative for RNA ISH. There were 4 cases that stained positively for IHC/ISH, 2 of which showed massive perivillous fibrin deposition, inflammation, and decidual arteriopathy. Coronavirus disease 2019 (COVID-19)-positive patients were more likely to self-identify as Hispanic and more likely to have public health insurance. Our data suggests SARS-CoV-2 exposed placentas that stain positively for SARS-CoV-2 show abnormal fibrin deposition, inflammatory changes, and decidual arteriopathy. The group of patients with clinical COVID-19 are more likely to show chronic villitis. IHC and ISH evidence of viral infection is rare.

Placental Histopathologic Findings of a Large Cohort of Patients With SARS-CoV-2 Infection During Pregnancy

Pregnant individuals with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are at a higher risk for adverse pregnancy outcomes. Previous small cohort studies have shown increased frequency of placental lesions associated with maternal vascular malperfusion, fetal vascular malperfusion, and inflammation among patients with SARS-CoV-2, without controlling for cardiometabolic risk factors among many such patients. We aimed to evaluate whether SARS-CoV-2 infection during pregnancy is independently associated with placental abnormalities when controlling for risk factors that could affect placental histopathology. Retrospective cohort study of placentas from singleton pregnancies in Kaiser Permanente Northern California from March to December 2020. Pathologic findings were compared among those with confirmed cases of SARS-CoV-2 during pregnancy and those without. We examined the association between SARS-CoV-2 infection and categorical placental pathologies, controlling for maternal age, gestational age, prepregnancy body mass index, gestational hypertension, preeclampsia/eclampsia, preexisting diabetes, history of thrombosis, and stillbirth. A total of 2,989 singleton gestation placentas were analyzed, 416 (13%) from pregnancies with SARS-CoV-2 infection and 2,573 (86%) from those without infection. Among placentas from pregnancies with SARS-CoV-2, 54.8% had evidence of inflammation, 27.1% maternal malperfusion abnormality, 20.7% massive perivillous fibrin or chronic villitis, 17.3% villous capillary abnormality, and 15.1% fetal malperfusion. After controlling for risks factors and stratifying interval time between SARS-CoV-2 infection and delivery, no association was found between placental abnormalities and SARS-CoV-2 infection during pregnancy. SARS-CoV-2 infection was not associated with an increased risk of placentally mediated adverse outcomes during pregnancy, compared with placentas sent for other indications, in this large diverse cohort.

The effects of COVID-19 on placental morphology

The impact of the COVID-19 infection, caused by Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), during the pandemic has been considerably more severe in pregnant women than non-pregnant women. Therefore, a review detailing the morphological alterations and physiological changes associated with COVID-19 during pregnancy and the effect that these changes have on the feto-placental unit is of high priority. This knowledge is crucial for these mothers, their babies and clinicians to ensure a healthy life post-pandemic. Hence, we review the placental morphological changes due to COVID-19 to enhance the general understanding of how pregnant mothers, their placentas and unborn children may have been affected by this pandemic. Based on current literature, we deduced that COVID-19 pregnancies were oxygen deficient, which could further result in other pregnancy-related complications like preeclampsia and IUGR. Therefore, we present an up-to-date review of the COVID-19 pathophysiological implications on the placenta, covering the function of the placenta in COVID-19, the effects of this virus on the placenta, its functions and its link to other gestational complications. Furthermore, we highlight the possible effects of COVID-19 therapeutic interventions on pregnant mothers and their unborn children. Based on the literature, we strongly suggest that consistent surveillance for the mothers and infants from COVID-19 pregnancies be prioritised in the future. Though the pandemic is now in the past, its effects are long-term, necessitating the monitoring of clinical manifestations in the near future.

COVID-19 Disease in Under-5 Children: Current Status and Strategies for Prevention including Vaccination

Since the coronavirus disease (COVID-19) pandemic hit the globe in early 2020, we have steadily gained insight into its pathogenesis; thereby improving surveillance and preventive measures. In contrast to other respiratory viruses, neonates and young children infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have a milder clinical presentation, with only a small proportion needing hospitalization and intensive care support. With the emergence of novel variants and improved testing services, there has been a higher incidence of COVID-19 disease reported among children and neonates. Despite this, the proportion of young children with severe disease has not increased. Key mechanisms that protect young children from severe COVID-19 disease include the placental barrier, differential expression of angiotensin-converting enzyme 2 (ACE-2) receptors, immature immune response, and passive transfer of antibodies via placenta and human milk. Implementing mass vaccination programs has been a major milestone in reducing the global disease burden. However, considering the lower risk of severe COVID-19 illness in young children and the limited evidence about long-term vaccine safety, the risk-benefit balance in children under five years of age is more complex. In this review, we do not support or undermine vaccination of young children but outline current evidence and guidelines, and highlight controversies, knowledge gaps, and ethical issues related to COVID-19 vaccination in young children. Regulatory bodies should consider the individual and community benefits of vaccinating younger children in their local epidemiological setting while planning regional immunization policies.

SARS-CoV-2 in Pregnancy, Birth and Puerperium. Guideline of the DGGG und DGPM (S2k-Level, AWMF Registry Number 015/092, March 2022)

Objective This S2k guideline of the German Society for Gynecology and Obstetrics (DGGG) and the German Society of Perinatal Medicine (DGPM) contains consensus-based recommendations for the care and treatment of pregnant women, parturient women, women who have recently given birth, and breastfeeding women with SARS-CoV-2 infection and their newborn infants. The aim of the guideline is to provide recommendations for action in the time of the COVID-19 pandemic for professionals caring for the above-listed groups of people.

Methods The PICO format was used to develop specific questions. A systematic targeted search of the literature was carried out using PubMed, and previously formulated statements and recommendations issued by the DGGG and the DGPM were used to summarize the evidence. This guideline also drew on research data from the CRONOS registry. As the data basis was insufficient for a purely evidence-based guideline, the guideline was compiled using an S2k-level consensus-based process. After summarizing and presenting the available data, the guideline authors drafted recommendations in response to the formulated PICO questions, which were then discussed and voted on.

Recommendations Recommendations on hygiene measures, prevention measures and care during pregnancy, delivery, the puerperium and while breastfeeding were prepared. They also included aspects relating to the monitoring of mother and child during and after infection with COVID-19, indications for thrombosis prophylaxis, caring for women with COVID-19 while they are giving birth, the presence of birth companions, postnatal care, and testing and monitoring the neonate during rooming-in or on the pediatric ward.

Histopathological Changes in Placenta of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Cov-2) Infection and Maternal and Perinatal Outcome in COVID-19

Background

Whether vertical transmission or placental pathology occurs after maternal infection during pregnancy remains unknown. There is a clear need for studies on the impact of COVID-19 on pregnancy outcome. A systemic inflammatory or hypercoagulable state may be the contributing factor for placental pathology.

Methods

The pregnant women with COVID-19 who delivered between May 2020 and May 2021 were followed and data were collected about pregnancy course and placentas were examined for macro- and microscopical changes and were compared to controls with non-infected women.

Results

Placenta of COVID-19-infected females had increased prevalence of decidual arteriopathy and placental injury reflecting hypoxia and uteroplacental insufficiency within the intervillous space. Features of maternal vascular malperfusion such as increased syncytial knots were present in 100% cases. Fibrinoid necrosis was seen in 100% cases and increased focal perivillous fibrin depositions were presented in 37.7% cases. About one fourth infected placentas had evidence of villitis. Even after matching for comorbidities like preeclampsia, these changes were present.

Conclusion

The most common pathological findings of the placenta of COVID-19 infections are signs of maternal and fetal malperfusion. Future studies should target infections in different stage of gestation, including first and second trimesters.

Impact of COVID-19 during pregnancy on placental pathology, maternal and neonatal outcome - A cross-sectional study on anemic term pregnant women from a tertiary care hospital in southern India

BACKGROUND

SARS-CoV-2 infection during pregnancy may cause adverse maternal, neonatal and placental outcomes. While tissue hypoxia is often reported in COVID-19 patients, pregnant women with anemia are suspected to be more prone to placental hypoxia-related injuries.

METHODS

This hospital-based cross-sectional study was conducted between August-November 2021, during COVID-19 second wave in India. Term pregnant women (N=212) admitted to hospital for delivery were enrolled consecutively. Since hospital admission mandated negative RT-PCR test for SARS-CoV-2 virus, none had active infection. Data on socio-demography, COVID-19 history, maternal, obstetric, and neonatal outcomes were recorded. Pre-delivery maternal and post-delivery cord blood samples were tested for hematological parameters and SARS-CoV-2 IgG. Placentae were studied for histology.

RESULTS

Of 212 women, 122 (58%) were seropositive for SARS-CoV-2 IgG, but none reported COVID-19 history; 134 (63.2%) were anemic. In seropositive women, hemoglobin (p=0.04), total WBC (p=0.009), lymphocytes (p=0.005) and neutrophils (p=0.02) were significantly higher, while ferritin was high, but not significant and neutrophils to lymphocytes (p=0.12) and platelets to lymphocytes ratios (p=0.03) were lower. Neonatal outcomes were similar. All RBC parameters and serum ferritin were significantly lower in anemic mothers but not in cord blood, except RDW that was significantly higher in both, maternal (p=0.007) and cord (p=0.008) blood from seropositive anemic group compared to other groups. Placental histology showed significant increase in villous hypervascularity (p=0.000), dilated villous capillaries (p=0.000), and syncytiotrophoblasts (p=0.02) in seropositive group, typically suggesting placental hypoxia. Maternal anemia was not associated with any histological parameters. Univariate and multivariate logistic regression analyses of placental histopathological adverse outcomes showed strong association with SARS-CoV-2 seropositivity but not with maternal anemia. When adjusted for several covariates, including anemia, SARS-CoV-2 seropositivity emerged as independent risk factor for severe chorangiosis (AOR 8.74, 95% CI 3.51-21.76, p<0.000), dilated blood vessels (AOR 12.74, 95% CI 5.46-29.75, p<0.000), syncytiotrophoblasts (AOR 2.86, 95% CI 1.36-5.99, p=0.005) and villus agglutination (AOR 9.27, 95% CI 3.68-23.32, p<0.000).

CONCLUSION

Asymptomatic COVID-19 during pregnancy seemed to be associated with various abnormal placental histopathologic changes related to placental hypoxia independent of maternal anemia status. Our data supports an independent role of SARS-CoV-2 in causing placental hypoxia in pregnant women.

PREGNANT WOMEN WITH COVID-19 AND PLACENTA ANGIOGENESIS

OBJECTIVE

Aim of our research was to conduct a clinical and laboratory analysis of the impact of COVID-19 on pregnancy and the condition of the fetus.

PATIENTS AND METHODS

Materials and Methods: At the first stage, we conducted a retrospective examination of 50 pregnant women treated at Ternopil Municipal Hospital No.2 (Ukraine) between November 2020 and January 2022 with the history of COVID-19, confirmed by PCR test, and 25 pregnant COVID-19 negative pregnant women (control group). At the second stage, we performed prospective cohort study and involved 40 pregnant women treated with the history of COVID-19, confirmed by PCR, and 10 pregnant COVID-19 negative women with a physiological course of pregnancy as a control group.Women were divided into the following groups: group I -10 women diagnosed with COVID-19 during the first trimester of pregnancy: group II-15 women diagnosed during the second trimester; group III-15 women diagnosed during the third trimester. Ultrasound examination and cardiotocograms were performed to assess fetus status. Blood samples were collected at delivery. To determine whether COVID-19 could alter placental angiogenesis, vascular endothelial growth factor A (VEGFA), PlGF and interleuin-32-α were assessed.

RESULTS

Results: We identified that concentration of VEGFA was 95.30±5.65 pg/ml in control group. In women who had COVID-19 in first trimester, this index was 1.3 times higher, in second trimester 1.63 times higher and in third trimester by 2 times compared to control group. PlGF concentration was only 27,4 percent in group I, 16 percent in group II and 30 percent in group III,compared to control group. Concentration of interleuin-32-α was 67.27±5.63 pg/ml in control group and increased to 167 percent in group I, by 2.8 times in group II and by 6.3 times in group III compared to control group.

CONCLUSION

Conclusions: COVID-19 has a negative impact on placental angiogenesis, including VEGFA and PlGF. Fetal post-COVID-19 syndrome requires timely diagnosis of disorders and further study. Post-COVID-19 syndrome is an immune-dependent pathology in which the processes of protracted cytokine activation occur in the body of a pregnant woman.

COVID-19 on Pregnancy Outcomes, Mental Health and Placenta: Focus in Latin America

The COVID-19 pandemic has impacted many aspects of health and society worldwide. One vulnerable group that faced SARS-CoV-2 infection is pregnant women, who were considered to have potentiated risk factors. In physiological pregnancy, maternal systems have several changes and adaptations to support fetal development. These changes involve regulations of cardiovascular, respiratory, and immunologic systems, among others, which SARS-CoV-2 could severely alter. Furthermore, the systemic effects of viral infection could be associated with placental dysfunction and adverse pregnancy outcomes, which have been studied from the start of the pandemic to date. Additionally, pregnancy is a condition of more significant mental health vulnerability, especially when faced with highly stressful situations. In this chapter, we have collected information on the effect of COVID-19 on maternal mortality, the SARS-CoV-2 infection rate in pregnancy, and the impact on pregnancy outcomes, maternal mental health, and placental function, with a particular focus on studies that consider the Latin American population.

SARS-CoV-2 (COVID-19) as a possible risk factor for neurodevelopmental disorders

Pregnant women constitute one of the most vulnerable populations to be affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the cause of coronavirus disease 2019. SARS-CoV-2 infection during pregnancy could negatively impact fetal brain development via multiple mechanisms. Accumulating evidence indicates that mother to fetus transmission of SARS-CoV-2 does occur, albeit rarely. When it does occur, there is a potential for neuroinvasion via immune cells, retrograde axonal transport, and olfactory bulb and lymphatic pathways. In the absence of maternal to fetal transmission, there is still the potential for negative neurodevelopmental outcomes as a consequence of disrupted placental development and function leading to preeclampsia, preterm birth, and intrauterine growth restriction. In addition, maternal immune activation may lead to hypomyelination, microglial activation, white matter damage, and reduced neurogenesis in the developing fetus. Moreover, maternal immune activation can disrupt the maternal or fetal hypothalamic-pituitary-adrenal (HPA) axis leading to altered neurodevelopment. Finally, pro-inflammatory cytokines can potentially alter epigenetic processes within the developing brain. In this review, we address each of these potential mechanisms. We propose that SARS-CoV-2 could lead to neurodevelopmental disorders in a subset of pregnant women and that long-term studies are warranted.

Fetoplacental transmission and placental response to SARS-CoV-2: Evidence from the literature

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a dreadful novel coronavirus with global health concerns among pregnant women. To date, the vertical transmission of SARS-CoV-2 during pregnancy remains controversial. We briefly report recent findings of placental response to SARS-CoV-2 infection and updates on vertical transmission. We systematically searched PubMed and Google Scholar databases according to PRISMA guidelines for studies reporting the effects of SARS-CoV-2 infection on the placenta and possibility of vertical transmission. We identified 45 studies reporting 1,280 human placentas that were analyzed by molecular pathology methods and 11,112 placenta-derived cells from a publicly available database that was analyzed using bioinformatics tools. The main finding of this study is that the SARS-CoV-2 canonical entry receptors (ACE2 and TMPRSS2) are abundantly expressed on the placenta during the first trimester, and this expression diminishes across gestational age. Out of 45 eligible studies identified, 24 (53.34%) showed no evidence of vertical transmission, 15 (33.33%) supported the hypothesis of very rare, low possibility of vertical transmission and 6 (13.33%) were indecisive and had no comment on vertical transmission. Furthermore, 433 placentas from 12 studies were also identified for placental pathology investigation. There was evidence of at least one form of maternal vascular malperfusion (MVM), 57/433 (13.1%), fetal vascular malperfusion (FVM), 81/433 (18.7%) and placental inflammation with excessive infiltration of CD3+ CD8+ lymphocytes, CD68+ macrophages and CD20+ lymphocytes in most of the eligible studies. Decidual vasculopathy (3.2%), infarction (3.2%), chronic histiocytic intervillositis (6.0%), thrombi vasculopathy (5.1%) were also observed in most of the MVM and FVM reported cases. The results indicated that SARS-CoV-2 induces placenta inflammation, and placenta susceptibility to SARS-CoV-2 decreases across the pregnancy window. Thus, SARS-CoV-2 infection in early pregnancy may adversely affect the developing fetus.

Coronavirus disease 2019 and the placenta: A literature review

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has been implicated in the clinical pathology of multiple organs and organ systems. Due to the novelty of the disease, there is a need to review emerging literature to understand the profile of SARS-CoV-2 in the placenta. This review sought to evaluate the literature on the mediators, mechanism of entry, pathogenesis, detection, and pathology of SARS-CoV-2 in the placenta. Systematic literature searches found 96 eligible studies. Our review revealed that SARS-CoV-2 canonical mediators, angiotensin-converting enzyme-2 (ACE2), and transmembrane serine protease-2 (TMPRSS2) are variably expressed in various placenta compartments, including the villous cytotrophoblasts, syncytiotrophoblasts (STBs), and extravillous trophoblasts (EVTs) throughout pregnancy. Placental SARS-CoV-2 and coronavirus-associated receptors and factors (SCARFs), including basigin (BSG/CD147), dipeptidyl peptidase-4 (DPP4/CD26), cathepsin B/L (CTL B/L), furin, interferon-induced transmembrane protein (IFITM1-3), and lymphocyte antigen 6E (LY6E) may increase or reduce the permissiveness of the placenta to SARS-CoV-2. EVTs express genes that code for proteins that may drive viral pathogenesis in the placenta. Viral RNA, proteins, and particles were detected primarily in the STBs by in situ hybridization, immunohistochemistry, electron microscopy, and polymerase chain reaction. Placental pathology in SARS-CoV-2-infected placentas included maternal and fetal vascular malperfusion and a generally nonspecific inflammatory-immune response. The localization of SARS-CoV-2 receptors, proteases, and genes involved in coding proteins that drive viral pathogenesis in the placenta predisposes the placenta to SARS-CoV-2 infection variably in all pregnancy trimesters, with antecedent placental pathology. There is a need for further studies to explicate the mechanism of entry and pathogenesis of SARS-CoV-2 in the placenta.

COVID-19: the possibility, ways, mechanisms, and interruptions of mother-to-child transmission

Background

In December 2019, novel coronavirus pneumonia was detected in Wuhan, Hubei Province, China, and as the epidemic spread, such cases emerged worldwide. Recently, the World Health Organization (WHO) named a new mutant Omicron (B.1.1.529), which disrupts the binding of most antibodies to the S protein and has a greater ability to break through the vaccine, posing a serious risk to population safety. Positive pregnant women give birth to positive newborns despite appropriate isolation measures taken by medical staff, suggesting that we may have vertical transmission of the novel coronavirus. This article analyzes and studies the possible vertical transmission path of the new coronavirus in the perinatal period of pregnant women and the antibody-dependent enhancement (ADE), and puts forward effective preventive measures for positive pregnant women to provide further reference for clinical work.

Methods

We searched multiple databases, including PubMed, CNKI, Google Scholar, WHO COVID-19 database, and CDC database. Search terms included COVID-19, SARS-CoV-2, vertical transmission, Omicron, Vaginal, Breast Feeding, Vaccine, Neonatal, Severe acute respiratory syndrome coronavirus, Pregnancy, and Semen.

Selection criteria

The following criteria were also met: (1) positive maternal novel coronavirus nucleic acid test; (2) reporting of neonatal outcome; (3) language in Chinese or English; (4) study date or location indicated; (5) no suspected or confirmed duplicated reports.

Results

There is evidence of vertical transmission, and the risk of possible vertical transmission is 5.7% (75/1314). The article listed four possible vertical transmission routes, namely placental transmission, vaginal upstream transmission, breastfeeding transmission and monocyte, and macrophage transmission route, with placental transmission being the most probable. Meanwhile, SARS-CoV-2 may also enter the placenta to infect the fetus through antibody-dependent enhanced substitution mechanism. We recommend three methods for early surveillance of vertical transmission, namely nucleic acid testing, antibody screening, and antigen testing, and analyze their advantages and disadvantages. Finally, the article provides recommendations in four areas: labor management, neonatal management, nosocomial infection prevention and control, and vaccination. As well as suggesting effective preventive measures for positive pregnant women and analyzing the advantages and disadvantages of vaccination, it is recommended that pregnant women should be vaccinated promptly, but considering that the vaccine may cause fever, it is recommended to consider vaccination cautiously in the first trimester of pregnancy.

Conclusion

The article concludes that vertical transmission is possible, with placental transmission being the most likely, and that the risk of possible vertical transmission is 5.7% (75/1314). Good personal protection, patient isolation, ward disinfection, and vaccination are the best means of interrupting SARS-CoV-2.

Pathological involvement of placenta in COVID-19: a systematic review

The mammalian placenta, which is responsible for bonding between the mother and the fetus, is one of the first organs to develop. Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection has caused a great threat to public health and affected almost all the organs including the placenta. Owing to limited available data on vertical transmission and pathological changes in the placenta of SARS-CoV-2 positive patients, we aim to review and summarize histopathological and ultrastructural changes in the placental tissue following SARS-CoV-2 infection. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2009 guidelines were used for review writing. Multiple studies have reported significant pathological changes in the placental tissue of SARS-CoV-2 positive mothers. On the other hand, some studies have demonstrated either no or very little involvement of the placental tissue. The most common pathological changes reported are fetal and maternal vascular malformation, villitis of unknown etiology, thrombus formation in the intervillous space and sub-chorionic space, and chorangiosis. Reports on vertical transmission are less in number. The observations of this review present a strong base for the pathological involvement of the placenta in SARS-CoV-2 infected mothers. However, a smaller number of original studies have been done until now, and most of them have small sample sizes and lack matched control groups, which are the big limitations for drawing an effective conclusion at this stage. Antenatal care can be improved by a better understanding of the correlation between maternal SARS-CoV-2 infection and placental pathology in COVID-19.

SARS-CoV-2 infection and COVID-19 vaccination in pregnancy

SARS-CoV-2 infection poses increased risks of poor outcomes during pregnancy, including preterm birth and stillbirth. There is also developing concern over the effects of SARS-CoV-2 infection on the placenta, and these effects seem to vary between different viral variants. Despite these risks, many pregnant individuals have been reluctant to be vaccinated against the virus owing to safety concerns. We now have extensive data confirming the safety and effectiveness of COVID-19 vaccination during pregnancy, although it will also be necessary to determine the effectiveness of these vaccines specifically against newly emerging viral variants, including Omicron. In this Progress article, I cover recent developments in our understanding of the risks of SARS-CoV-2 infection in pregnancy, and how vaccination can reduce these.

Placental Ultrasonographical Findings during SARS-CoV-2 Infection

Infection with SARS-CoV-2 virus (COVID-19) during pregnancy has been associated with several complications. Increasing evidence suggests that COVID-19 infection leaves tell-tale signs of placental injury. During ultrasound examination and placental evaluation of COVID-19 infected pregnancies, we recorded signs of placental involvement, with findings indicating malperfusion, chorangiosis, deciduitis, and subchorionitis. Early detection of placental damage through the use of specific ultrasound findings could indicate which pregnancies are at increased risk for complications.

Inflammatory responses in the placenta upon SARS-CoV-2 infection late in pregnancy

The effect of SARS-CoV-2 infection on placental function is not well understood. Analysis of placentas from women who tested positive at delivery showed SARS-CoV-2 genomic and subgenomic RNA in 22 out of 52 placentas. Placentas from two mothers with symptomatic COVID-19 whose pregnancies resulted in adverse outcomes for the fetuses contained high levels of viral Alpha variant RNA. The RNA was localized to the trophoblasts that cover the fetal chorionic villi in direct contact with maternal blood. The intervillous spaces and villi were infiltrated with maternal macrophages and T cells. Transcriptome analysis showed an increased expression of chemokines and pathways associated with viral infection and inflammation. Infection of placental cultures with live SARS-CoV-2 and spike protein-pseudotyped lentivirus showed infection of syncytiotrophoblast and, in rare cases, endothelial cells mediated by ACE2 and Neuropilin-1. Viruses with Alpha, Beta, and Delta variant spikes infected the placental cultures at significantly greater levels.

Severe Acute Respiratory Syndrome Coronavirus 2 Infection in Pregnancy. A Non-systematic Review of Clinical Presentation, Potential Effects of Physiological Adaptations in Pregnancy, and Placental Vascular Alterations

In December 2019, the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) rapidly spread to become a pandemic. To date, increasing evidence has described the potential negative impact of SARS-CoV-2 infection on pregnant women. Although the pathophysiology of coronavirus disease 2019 (COVID-19) is not entirely understood, there is emerging evidence that it causes a severe systemic inflammatory response associated with vascular alterations that could be of special interest considering some physiological changes in pregnancy. Additionally, these alterations may affect the physiology of the placenta and are associated with pregnancy complications and abnormal histologic findings. On the other hand, data about the vaccine against SARS-CoV-2 are limited, but the risks of administering COVID-19 vaccines during pregnancy appear to be minimal. This review summarizes the current literature on SARSCoV2 virus infection, the development of COVID-19 and its relationship with physiological changes, and angiotensin-converting enzyme 2 (ACE2) function during pregnancy. We have particularly emphasized evidence coming from Latin American countries.

A review of the main placenta histopathological findings reported in coronavirus disease 2019

Several studies have reported that pregnant women are more susceptible to contracting the SARS-CoV-2 disease. However, SARS-CoV-2 infection studies have limited evidence regarding its impact on pregnancy, particularly its pathological effects on the maternal–fetal interface. This review emphasized the placental structures and immunomodulatory defense mechanism against the viral infection COVID and highlighted the spectrum of reported histopathological changes from SARS-CoV-2-infected mothers' placenta to contribute to the knowledge of the nature of this placental pathology. Further studies where collaborations that seek to maximize sample numbers analyzed can be performed to improve the generalizability and reliability of the findings. This can lead to improved knowledge on the relationship between placental dysfunction and pathology from maternal SARS-CoV-2 infection. Consequently, this can help improve maternity care delivery during the pandemic.

A Standardization Protocol for the In Situ Detection of SARS-CoV2 RNA and Proteins

This manuscript details a stringent protocol for the in situ detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) RNA and 4 different viral proteins: envelope, spike, membrane, and nucleocapsid. Key aspects of the protocol are: (1) analysis of adjacent (serial) sections for viral RNA and at least 2 viral proteins; (2) cytologic alterations in the cells scored as virus positive based on an hematoxylin and eosin stain; (3) in situ demonstration of a host response in the cells scored as virus positive; (4) co-labeling experiments that show that the viral RNA and/or proteins co-localize with each other and the angiotensin converting enzyme 2 (ACE2) receptor; and (5) lack of signal in equivalent tissues obtained before the pandemic. Optimization conditions for the four viral proteins as well as the ACE2 receptor were each antigen retrieval in an EDTA solution which facilitates co-expression analyses. It is recommended not to use either electron microscopy or qRTPCR as methods to corroborate in situ SARS-CoV2 detection. This stringent protocol, that relies on sequentially labeled serial sections and can be completed in one working day, demonstrated the following: (1) infectious SARS-CoV2 is abundant in the lung in fatal coronavirus disease-2019 and is seen primarily in macrophages and endothelial cells; (2) circulating viral capsid proteins (spike, envelope, membrane without RNA) are evident in multiple organs including the skin and brain where it is endocytosed by ACE2+ cells and induce an endothelialitis; (3) both the infectious virus and circulating spike protein induce complement activation and cytologic changes in the viral positive cells.

SARS-CoV-2 and Placental Pathology: Malperfusion Patterns Are Dependent on Timing of Infection During Pregnancy

The extent to which severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection at different points in the pregnancy timeline may affect maternal and fetal outcomes remains unknown. We sought to characterize the impact of SARS-CoV-2 infection proximate and remote from delivery on placental pathology. We performed a secondary analysis of placental pathology from a prospective cohort of universally tested SARS-CoV-2 positive women >20 weeks gestation at 1 institution. Subjects were categorized as having acute or nonacute SARS-CoV-2 based on infection <14 or ≥14 days from delivery admission, respectively, determined by nasopharyngeal swab, symptom history, and serologies, when available. A subset of SARS-CoV-2 negative women represented negative controls. Placental pathology was available for 90/97 (92.8%) of SARS-CoV-2 positive women, of which 26 were from women with acute SARS-CoV-2 infection and 64 were from women with nonacute SARS-CoV-2. Fetal vascular malperfusion lesions were significantly more frequent among the acute SARS-CoV-2 group compared with the nonacute SARS-CoV-2 group (53.8% vs. 18.8%; P=0.002), while frequency of maternal vascular malperfusion lesions did not differ by timing of infection (30.8% vs. 29.7%; P>0.99). When including 188 SARS-CoV-2 negative placentas, significant differences in frequency of fetal vascular malperfusion lesions remained between acute, nonacute and control cases (53.8% vs. 18.8% vs. 13.2%, respectively; P<0.001). No differences were noted in obstetric or neonatal outcomes between acutely and nonacutely infected women. Our findings indicate timing of infection in relation to delivery may alter placental pathology, with potential clinical implications for risk of thromboembolic events and impact on fetal health.

[Review of new evidence about the possible vertical transmission of coronavirus disease-2019]

OBJECTIVE

To conduct a systematic review of original peer-reviewed studies, containing data on the identification of SARS-CoV-2 in clinical samples of amniotic fluid, placenta or membranes, umbilical cord blood, and human milk, from women with a clinically or confirmed diagnosis of COVID-19. These studies should have been published after the guide for the management of patients with COVID-19 from World Health Organization guide (available in March 13, 2020).

RESULTS

Seventeen studies were included, in which 143 clinical samples were identified (38 of amniotic fluid; 34 of placentas or membranes; 39 from umbilical cord blood and 32 from human milk). Among the 143 samples, nine were positive for SARS-CoV-2 RNA (one amniotic fluid sample obtained before rupturing the membranes; six samples of placenta or membranes, although authors indicate the possibility of contamination by maternal blood in three of these, and two samples of human milk).

CONCLUSIONS

Following our search criteria, we found no studies that demonstrate the detection of SARS-CoV-2, in conjunction with viral isolation and the evaluation of the infective capacity of viral particles, in clinical samples of amniotic fluid, placenta or membranes, umbilical cord blood and human milk, from women with a confirmed or clinical diagnosis of COVID-19. However, vertical transmission cannot be ruled out, larger studies are required that ideally locate in situ RNA and protein of SARS-CoV-2, as well as isolation that demonstrate the infective capacity of the viral particles.

The Effect of COVID-19 Infection During Pregnancy; Evaluating Neonatal Outcomes and the Impact of the B.1.1.7. Variant

BACKGROUND

Coronavirus disease 2019 (COVID-19) infection during pregnancy has been associated with adverse perinatal outcomes. We aim to evaluate the neonatal outcomes including the incidence of preterm birth, admission to the neonatal unit and incidence of congenital anomalies in this cohort. We will also describe these outcomes in the context of the B.1.1.7. variant outbreak, the dominant variant in Ireland since January 2021, which has had a greater impact on pregnant patients.

METHODS

This was a retrospective study of liveborn infants, delivered between 1st March 2020 and 1st March 2021, to women with a severe acute respiratory syndrome coronavirus 2 diagnosis during pregnancy, in a tertiary maternity hospital (8,500 deliveries/year). Clinical data were collected, and analyses were performed to evaluate the impact of maternal symptom status, time from diagnosis to delivery and the B.1.1.7. variant on neonatal outcome.

RESULTS

In total 133 infants (1.6%) were born to women with severe acute respiratory syndrome coronavirus 2 identified during pregnancy. The median birth weight was 3.45 kg and gestational age at birth was 39.3 weeks. 14 infants (10.5%) were preterm. 22 infants (16.5%) required admission to the neonatal unit and 7 (5.3%) were small for gestational age. There was no difference in growth, preterm birth or neonatal unit admission based on maternal symptom status or infection after the outbreak of B.1.1.7. as the dominant strain.

CONCLUSIONS

Following a COVID-19 infection in pregnancy, there was no increase in the incidence of preterm birth or neonatal intensive care unit admission compared with 5-year hospital data. Maternal symptom status did not influence neonatal outcomes. Further studies to evaluate the impact of COVID-19 in early pregnancy, the variants of concern, particularly the emerging Delta variant and COVID-19 placentitis are required.

COVID-19 in pregnancy: What we know from the first year of the pandemic

The COVID-19 pandemic has infected nearly 178 million people and claimed the lives of over 3.8 million in less than 15 months. This has prompted a flurry of research studies into the mechanisms and effects of SARS-CoV-2 viral infection in humans. However, studies examining the effects of COVID-19 in pregnant women, their placentae and their babies remain limited. Furthermore, reports of safety and efficacy of vaccines for SARS-CoV-2 in pregnancy are limited. This review concisely summarises the case studies and research on COVID-19 in pregnancy, to date. It also reviews the mechanism of infection with SARS-CoV-2, and its reliance and effects upon the renin-angiotensin-aldosterone system. Overall, the data suggest that infection during pregnancy can be dangerous at any time, but this risk to both the mother and fetus, as well as placental damage, increases during the third trimester. The possibility of vertical transmission, which is explored in this review, remains contentious. However, maternal infection with SARS-CoV-2 can increase risk of miscarriage, preterm birth and stillbirth, which is likely due to damage to the placenta.

Frequent Placental SARS-CoV-2 in Patients with COVID-19-Associated Hypertensive Disorders of Pregnancy

Introduction

Studies described an increased frequency of hypertensive disorders of pregnancy (HDP) after a COVID-19 episode. There is limited evidence about SARS-CoV-2 viral load in placenta. This study aimed to investigate the relationship between SARS-CoV-2 viral load in the placenta and clinical development of HDP after COVID-19 throughout different periods of gestation.

Methods

This is a case-control study in women with and without gestational hypertensive disorders after SARS-CoV-2 infection diagnosed by RT-PCR during pregnancy. Patients were matched by gestational age at the moment of COVID-19 diagnosis. We performed an analysis of SARS-CoV-2 RNA levels in placenta.

Results

A total of 28 women were enrolled. Sixteen patients were diagnosed with COVID-19 during the third trimester and the remaining 12 patients in the other trimesters. Ten placentas (35.7%) were positive for SARS-CoV-2, 9 of them (9/14, 64.3%) belonged to the HDP group versus 1 (1/14, 7.2%) in the control group (p = 0.009). Those cases with the highest loads of viral RNA developed severe preeclampsia (PE).

Conclusion

Among women diagnosed with COVID-19 during pregnancy, the presence of SARS-CoV-2 in the placenta was more frequent among women suffering from PE or gestational hypertension. Furthermore, the most severe cases of HDP were associated with high placental viral load, not necessarily associated with a positive nasopharyngeal RT-PCR at delivery. Our data suggest that SARS-CoV-2 infection during pregnancy could trigger gestational hypertensive disorders through persistent placental infection and resulting placental damage.

The immunologic response to severe acute respiratory syndrome coronavirus 2

Background: The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has precipitated the worst global pandemic in a century, which has caused millions of infections and deaths as well as massive economic repercussions. Objective: As with any pathogenic virus, it is crucial to understand its unique interactions with the human immune system so that pharmaceutical and prophylactic interventions can be deployed to effectively control the pandemic. Methods: A literature search by using PubMed was conducted in 2020 with variants of the terms "COVID-19," "SARS-CoV-2," and "immunological response." English language articles that presented original data about the immunologic response to coronavirus disease 2019 (COVID-19) were selected for review. This article reviewed the current understanding of the innate and adaptive immune responses to SARS-CoV-2 infection, including their relationship to current therapeutic and diagnostic strategies. Results: SARS-CoV-2 uses several unique molecular techniques to evade detection by the innate immune system early in the course of infection, and upregulation of these innate immune pathways may possibly accelerate the time to recovery and prevent severe disease. Although the majority of cases results in the patients' recovery, a significant proportion of infections result in deaths prompted by the host's inflammatory overreaction to the infection, a response that can be attenuated with corticosteroids and potentially other immune modulators. Conclusion: Current work by the scientific community to further understand how SARS-CoV-2 interacts with the human immune system will be invaluable to our response and preparedness for future coronavirus pandemics.

Placental histopathology after SARS-CoV-2 infection in pregnancy: a systematic review and meta-analysis

OBJECTIVE

This study aimed to report the spectrum of placental pathology findings in pregnancies complicated by SARS-CoV-2 infection.

DATA SOURCES

MEDLINE, Embase, Google Scholar, and the Web of Science databases were searched up to August 11, 2021.

STUDY ELIGIBILITY CRITERIA

Histopathologic anomalies included maternal vascular malperfusion, fetal vascular malperfusion, acute inflammatory pathology, chronic inflammatory pathology, increased perivillous fibrin, and intervillous thrombosis. Moreover, subanalyses of symptomatic women only and high-risk pregnancies were performed.

METHODS

Histopathologic analysis of the placenta included gross examination, histopathology on hematoxylin and eosin, immunohistochemistry, fluorescence in situ hybridization, quantitative reverse transcription-polymerase chain reaction on placental tissue, and transmission electron microscope. Random-effect meta-analyses were used to analyze the data.

RESULTS

A total of 56 studies (1008 pregnancies) were included. Maternal vascular malperfusion was reported in 30.7% of placentas (95% confidence interval, 20.3-42.1), whereas fetal vascular malperfusion was observed in 27.08 % of cases (95% confidence interval, 19.2-35.6). Acute and chronic inflammatory pathologies were reported in 22.68% (95% confidence interval, 16.9-29.0) and 25.65% (95% confidence interval, 18.4-33.6) of cases, respectively. Increased perivillous fibrin was observed in 32.7% (95% confidence interval, 24.1-42.0) of placentas undergoing histopathologic analysis, whereas intervillous thrombosis was observed in 14.6% of cases (95% confidence interval, 9.7-20.2). Other placental findings, including a basal plate with attached myometrial fibers, microscopic accretism, villous edema, increased circulating nucleated red blood cells, or membranes with hemorrhage, were reported in 37.5% of cases (95% confidence interval, 28.0-47.5), whereas only 17.5% of cases (95% confidence interval, 10.9-25.2) did not present any abnormal histologic findings. The subanalyses according to maternal symptoms owing to SARS-CoV-2 infection or the presence of a high-risk pregnancy showed a similar distribution of the different histopathologic anomalies to that reported in the main analysis. Moreover, the risk of placental histopathologic anomalies was higher when considering only case-control studies comparing women with SARS-CoV-2 infection with healthy controls.

CONCLUSION

In pregnant women with SARS-CoV-2 infection, a significant proportion of placentas showed histopathologic findings, suggesting placental hypoperfusion and inflammation. Future multicenter prospective blinded studies are needed to correlate these placental lesions with pregnancy outcomes.

The skin as a critical window in unveiling the pathophysiologic principles of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), is a single-stranded RNA virus whose sequence is known. COVID-19 is associated with a heterogeneous clinical phenotype ranging from asymptomatic to fatal disease. It appears that access to nasopharyngeal respiratory epithelia expressing angiotensin-converting enzyme (ACE) 2, the receptor for SARS-CoV-2, is followed by viral replication in the pulmonary alveolar septal capillary bed. We have demonstrated in earlier studies that incomplete viral particles, termed pseudovirions, dock to deep subcutaneous and other vascular beds, potentially contributing to the prothrombotic state and systemic complement activation that characterizes severe and critical COVID-19. A variety of skin eruptions have been described in the setting of SARS-CoV-2 infection and more recently, after COVID-19 vaccination. The vaccines deliver a laboratory-synthesized mRNA that encodes a protein that is identical to the spike glycoprotein of SARS-CoV-2, allowing the production of immunogenic spike glycoprotein that will then elicit T cell and B cell adaptive immune responses. In this contribution, we review an array of cutaneous manifestations of COVID-19 that provide an opportunity to study critical pathophysiologic mechanisms that underlie all clinical facets of COVID-19, ranging from asymptomatic/mild to severe and critical COVID-19. We classify cutaneous COVID-19 according to underlying pathophysiologic principles. In this regard we propose three main pathways: (1) complement mediated thrombotic vascular injury syndromes deploying the alternative and mannan binding lectin pathways and resulting in the elaboration of cytokines like interleukin 6 from endothelium in the setting of severe and critical COVID-19 and (2) the robust T cell and type I interferon-driven inflammatory and (3) humoral-driven immune complex mediated vasculitic cutaneous reactions observed with mild and moderate COVID-19. Presented are novel data on cutaneous vaccine reactions that manifest a clinical and morphologic parallel with similar eruptions observed in patients with mild and moderate COVID-19 and in some cases represent systemic eczematoid hypersensitivity reactions to a putative vaccine-based antigen versus unmasking subclinical hypersensitivity due to immune enhancing effects of the vaccine. Finally, we demonstrate for the first time the localization of human synthesized spike glycoprotein after the COVID-19 vaccine to the cutaneous and subcutaneous vasculature confirming the ability of SARS-CoV-2 spike glycoprotein to bind endothelium in the absence of intact virus.

Haematological parameters and coagulation in umbilical cord blood following COVID-19 infection in pregnancy

Objective

The aim of this study was to evaluate infants, born to women with SARS-CoV-2 detected during pregnancy, for evidence of haematological abnormalities or hypercoagulability in umbilical cord blood.

Study design

This was a prospective observational case-control study of infants born to women who had SARS-CoV-2 RNA detected by PCR at any time during their pregnancy (n = 15). The study was carried out in a Tertiary University Maternity Hospital (8,500 deliveries/year) in Ireland. This study was approved by the Hospital Research Ethics Committee and written consent was obtained. Umbilical cord blood samples were collected at delivery, full blood count and Calibrated Automated Thrombography were performed. Demographics and clinical outcomes were recorded. Healthy term infants, previously recruited as controls to a larger study prior to the outbreak of COVID-19, were the historical control population (n = 10).

Results

Infants born to women with SARS-CoV-2 had similar growth parameters (birth weight 3600 g v 3680 g, p = 0.83) and clinical outcomes to healthy controls, such as need for resuscitation at birth (2 (13.3%) v 1 (10%), p = 1.0) and NICU admission (1 (6.7%) v 2 (20%), p = 0.54). Haematological parameters (Haemoglobin, platelet, white cell and lymphocyte counts) in the COVID-19 group were all within normal neonatal reference ranges. Calibrated Automated Thrombography revealed no differences in any thrombin generation parameters (lag time (p = 0.92), endogenous thrombin potential (p = 0.24), peak thrombin (p = 0.44), time to peak thrombin (p = 0.94)) between the two groups.

Conclusion

In this prospective study including eligible cases in a very large population of approximately 1500 women, there was no evidence of derangement of the haematological parameters or hypercoagulability in umbilical cord blood due to COVID-19. Further research is required to investigate the pathological placental changes, particularly COVID-19 placentitis and the impact of different strains of SARS-CoV-2 (particularly the B.1.1.7 and the emerging Delta variant) and the severity and timing of infection on the developing fetus.

COVID-19 in pregnancy: placental pathological patterns and effect on perinatal outcome in five cases

INTRODUCTION

COVID-19, the disease caused by the novel coronavirus SARS-CoV-2, is a severe systemic thrombotic syndrome that emerged in 2019, with an ensuing pandemic. To evaluate the impact of this disease on placental tissue and perinatal outcome, histological, immunohistochemical and ultrastructural analyses of placental tissue were performed for five cases of pregnant women with COVID-19.

CASE REPORTS

All five pregnant women in this series developed COVID-19 in late pregnancy. Two patients experienced respiratory distress, and computed tomography revealed signs of pneumonia, with bilateral involvement, multiple lobular and subsegmental areas of consolidation and ground-glass opacities. Histological studies of placental tissue revealed the presence of slight signs of maternal vascular underperfusion (MVUs) or foetal vascular underperfusion (FVUs) lesions and mild inflammatory lesions. CD15 immunoreactivity in the placental tissue was low in all cases, demonstrating that in these cases there was not severe foetal hypoxia/asphyxia risk for newborns or distal vascular immaturity. In all cases examined, ultrastructural analyses showed spherical-like coronavirus particles with an electron intermediate-density core as well as projections from the surface as spike-like structures in the syncytiotrophoblasts. At term, all of the women delivered newborns who were negative for SARS-CoV-2 by nasopharyngeal testing in their first day of life. All newborns were exclusively breastfed and were discharged on the 3rd day of life.

CONCLUSIONS

In conclusion, placental patterns in pregnancy due to COVID-19 in the late stage of gestation indicate no evidence of vertical trans-placental SARS-CoV-2 transmission or a significant impact on the perinatal outcome of newborns, in both mild and more severe cases.

Fetal pulmonary artery Doppler evaluation in pregnant women after recovery from COVID-19

Objective

To evaluate fetal lung development using pulmonary artery Doppler in pregnant women who had recovered from COVID‐19.

Methods

The prospective case–control study included 41 pregnant women who had recovered from COVID‐19 and 43 healthy pregnant women (control group). All the women in the study group had been diagnosed with COVID‐19 and had completed a quarantine period.

Results

The demographic data of patients were similar in the groups (P > 0.05). Main pulmonary artery peak systolic velocity was higher and pulsatility indices were lower in pregnant women who recovered from COVID‐19 compared to the controls (P < 0.001, P = 0.001). Acceleration time, ejection time, and acceleration/ejection time ratio (PATET) of the fetal MPA Doppler were significantly decreased in pregnant women who recovered from COVID‐19 (P < 0.001, P = 0.036, and P = 0.002, respectively). The patients who had recovered from COVID‐19 were divided into two groups: those treated with expectant management and those treated in hospital. The pulmonary artery acceleration time and PATET ratio were significantly lower in the group treated in the hospital (P = 0.023 and P = 0.045, respectively).

Conclusion

Detailed Doppler evaluations of the pulmonary artery may help in evaluating the fetal adverse effects of COVID‐19 disease.

Detailed Doppler evaluations of the pulmonary artery may help in evaluating the fetal adverse effects of COVID‐19 disease.

Placental histopathology after SARS-CoV-2 infection in pregnancy: a systematic review and meta-analysis

OBJECTIVE

This study aimed to report the spectrum of placental pathology findings in pregnancies complicated by SARS-CoV-2 infection.

DATA SOURCES

MEDLINE, Embase, Google Scholar, and the Web of Science databases were searched up to August 11, 2021.

STUDY ELIGIBILITY CRITERIA

Histopathologic anomalies included maternal vascular malperfusion, fetal vascular malperfusion, acute inflammatory pathology, chronic inflammatory pathology, increased perivillous fibrin, and intervillous thrombosis. Moreover, subanalyses of symptomatic women only and high-risk pregnancies were performed.

METHODS

Histopathologic analysis of the placenta included gross examination, histopathology on hematoxylin and eosin, immunohistochemistry, fluorescence in situ hybridization, quantitative reverse transcription-polymerase chain reaction on placental tissue, and transmission electron microscope. Random-effect meta-analyses were used to analyze the data.

RESULTS

A total of 56 studies (1008 pregnancies) were included. Maternal vascular malperfusion was reported in 30.7% of placentas (95% confidence interval, 20.3-42.1), whereas fetal vascular malperfusion was observed in 27.08 % of cases (95% confidence interval, 19.2-35.6). Acute and chronic inflammatory pathologies were reported in 22.68% (95% confidence interval, 16.9-29.0) and 25.65% (95% confidence interval, 18.4-33.6) of cases, respectively. Increased perivillous fibrin was observed in 32.7% (95% confidence interval, 24.1-42.0) of placentas undergoing histopathologic analysis, whereas intervillous thrombosis was observed in 14.6% of cases (95% confidence interval, 9.7-20.2). Other placental findings, including a basal plate with attached myometrial fibers, microscopic accretism, villous edema, increased circulating nucleated red blood cells, or membranes with hemorrhage, were reported in 37.5% of cases (95% confidence interval, 28.0-47.5), whereas only 17.5% of cases (95% confidence interval, 10.9-25.2) did not present any abnormal histologic findings. The subanalyses according to maternal symptoms owing to SARS-CoV-2 infection or the presence of a high-risk pregnancy showed a similar distribution of the different histopathologic anomalies to that reported in the main analysis. Moreover, the risk of placental histopathologic anomalies was higher when considering only case-control studies comparing women with SARS-CoV-2 infection with healthy controls.

CONCLUSION

In pregnant women with SARS-CoV-2 infection, a significant proportion of placentas showed histopathologic findings, suggesting placental hypoperfusion and inflammation. Future multicenter prospective blinded studies are needed to correlate these placental lesions with pregnancy outcomes.

Role of ACE2 in pregnancy and potential implications for COVID-19 susceptibility

In times of coronavirus disease 2019 (COVID-19), the impact of severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 infection on pregnancy is still unclear. The presence of angiotensin-converting enzyme (ACE) 2 (ACE2), the main receptor for SARS-CoV-2, in human placentas indicates that this organ can be vulnerable for viral infection during pregnancy. However, for this to happen, additional molecular processes are critical to allow viral entry in cells, its replication and disease manifestation, particularly in the placenta and/or feto-maternal circulation. Beyond the risk of vertical transmission, COVID-19 is also proposed to deplete ACE2 protein and its biological actions in the placenta. It is postulated that such effects may impair essential processes during placentation and maternal hemodynamic adaptations in COVID-19 pregnancy, features also observed in several disorders of pregnancy. This review gathers information indicating risks and protective features related to ACE2 changes in COVID-19 pregnancies. First, we describe the mechanisms of SARS-CoV-2 infection having ACE2 as a main entry door and current evidence of viral infection in the placenta. Further, we discuss the central role of ACE2 in physiological systems such as the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS), both active during placentation and hemodynamic adaptations of pregnancy. Significant knowledge gaps are also identified and should be urgently filled to better understand the fate of ACE2 in COVID-19 pregnancies and the potential associated risks. Emerging knowledge will be able to improve the early stratification of high-risk pregnancies with COVID-19 exposure as well as to guide better management and follow-up of these mothers and their children.

Defining Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Placentitis: A Report of 7 Cases with Confirmatory In Situ Hybridization, Distinct Histomorphologic Features, and Evidence of Complement Deposition

CONTEXT

-Case reports and rare case series have demonstrated variable placental pathology in the setting of maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In rare small studies demonstrating infection of the placental parenchyma, histologic manifestations have included variable degrees of histiocytic intervillositis, perivillous fibrin deposition, and syncytiotrophoblast necrosis.

OBJECTIVE

-To characterize the placental pathological features of SARS-CoV-2 infected placentas, irrespective of fetal-maternal transmission, and to examine the frequency of C4d activation in such cases.

DESIGN

-Retrospective study of seven placentas from mothers with active SARS-CoV-2 infection and placental infection as demonstrated by RNA in situ hybridization.

RESULTS

-Six placentas were from live-born neonates (5 singletons, 1 non-fused diamniotic-dichorionic twin placenta), and one was from a stillbirth. Five of the eight neonates (including the stillbirth) tested negative for SARS-CoV-2, and all were negative for neonatal infection. The remaining three neonates were well at time of discharge. All placentas were positive for SARS-CoV-2 infection by RNA in situ hybridization and demonstrated variable degrees of histiocytic intervillositis, perivillous fibrin deposition, and trophoblast necrosis. Three cases demonstrated features of fetal vascular malperfusion. CD68 highlighted intervillous histiocytes. C4d expression was present along the villous borders in 6 of 7 cases.

CONCLUSIONS

-SARS-CoV-2 placentitis is defined by the triad of histiocytic intervillositis, perivillous fibrin deposition, and trophoblast necrosis. The features may occur in cases without confirmed transplacental transmission. The damage caused by SARS-CoV-2 placentitis is likely mediated by complement activation.

Immunological and physiopathological approach of COVID-19 in pregnancy

Coronavirus disease-2019 (COVID-19) related to Coronavirus-2 (SARS-CoV-2) is a worldwide health concern. Despite the majority of patients will evolve asymptomatic or mild-moderate upper respiratory tract infections, 20% will develop severe disease. Based on current pathogenetic knowledge, a severe COVID-19 form is mainly a hyperinflammatory, immune-mediated disorder, triggered by a viral infection. Due to their particular immunological features, pregnant women are supposed to be particularly susceptible to complicate by intracellular infections as well as immunological disturbances. As an example, immune-thrombosis has been identified as a common immune-mediated and pathogenic phenomenon both in COVID-19, in obstetric diseases and in COVID-19 pregnant women. According to extensive published clinical data, is rationale to expect an interference with the normal development of pregnancy in selected SARS-CoV-2-infected cases, mainly during third trimester.This manuscript provides insights of research to elucidate the potential harmful responses to SARS-CoV-2 and /or other coronavirus infections, as well as bidirectional interactions between COVID-19 and pregnancy to improve their respective management.

SARS-CoV-2 Infects Syncytiotrophoblast and Activates Inflammatory Responses in the Placenta

SARS-CoV-2 infection during pregnancy leads to an increased risk of adverse pregnancy outcomes. Although the placenta itself can be a target of virus infection, most neonates are virus free and are born healthy or recover quickly. Here, we investigated the impact of SARS-CoV-2 infection on the placenta from a cohort of women who were infected late during pregnancy and had tested nasal swab positive for SARS-CoV-2 by qRT-PCR at delivery. SARS-CoV-2 genomic and subgenomic RNA was detected in 23 out of 54 placentas. Two placentas with high virus content were obtained from mothers who presented with severe COVID-19 and whose pregnancies resulted in adverse outcomes for the fetuses, including intrauterine fetal demise and a preterm delivered baby still in newborn intensive care. Examination of the placental samples with high virus content showed efficient SARS-CoV-2 infection, using RNA in situ hybridization to detect genomic and replicating viral RNA, and immunohistochemistry to detect SARS-CoV-2 nucleocapsid protein. Infection was restricted to syncytiotrophoblast cells that envelope the fetal chorionic villi and are in direct contact with maternal blood. The infected placentas displayed massive infiltration of maternal immune cells including macrophages into intervillous spaces, potentially contributing to inflammation of the tissue. Ex vivo infection of placental cultures with SARS-CoV-2 or with SARS-CoV-2 spike (S) protein pseudotyped lentivirus targeted mostly syncytiotrophoblast and in rare events endothelial cells. Infection was reduced by using blocking antibodies against ACE2 and against Neuropilin 1, suggesting that SARS-CoV-2 may utilize alternative receptors for entry into placental cells.

[Impact of SARS-CoV-2/COVID-19 on the placenta]

Ein besonderes Augenmerk bei der durch das Severe-acute-respiratory-syndrome-Coronavirus‑2 (SARS-CoV-2) hervorgerufenen Coronaviruskrankheit 2019 (COVID-19) wurde von Beginn an auf die Gruppe der Schwangeren gelegt.

Nach einer Einführung zur Immunabwehr der Plazenta und viralen plazentaren Infektionen, beschreiben wir die morphologischen Veränderungen der Plazenta bei SARS-CoV-2-Infektion der Mutter, ziehen Vergleiche zur SARS-Epidemie und diskutieren die Frage der vertikalen Transmission von SARS-CoV‑2 von der Mutter auf das Neugeborene.

Die häufigsten pathologischen Befunde der Plazenta bestehen in Zeichen der maternalen und auch fetalen Malperfusion sowie immunologisch bzw. thromboinflammatorisch vermittelten Veränderungen. Es finden sich Infarkte, deziduale Vaskulopathie sowie Thromben im fetalen Kreislauf und Vermehrung avaskulärer Villi. Daneben zeigen sich in einigen Fällen Entzündungsreaktionen mit Villitis und Intervillositis sowie eine Vaskulitis fetaler Gefäße. Zudem konnte der Nachweis erbracht werden, dass SARS-CoV‑2 die Plazenta direkt infizieren kann. Somit ist auch eine vertikale Transmission möglich.

Ein COVID-19-spezifisches Schädigungsmuster der Plazenta liegt bislang nicht vor, obwohl der Nachweis von fetaler Thrombovaskulitis, Villitis und Intervillositis sowie einer fetalen und maternalen Malperfusion in Analogie zu der bereits bekannten allgemeinen Pathophysiologie von COVID-19 (Entzündungsreaktion und Mikrozirkulationsstörung) interpretiert werden könnte. Der Nachweis viraler RNA in den fetalen Kompartimenten der Plazenta/der Nabelschnur zeugt von der vertikalen SARS-CoV‑2 Transmission.

Histologic and Immunohistochemical Evaluation of 65 Placentas From Women With Polymerase Chain Reaction-Proven Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection

CONTEXT.—

Coronavirus disease 2019 (COVID-19) has been shown to have effects outside of the respiratory system. Placental pathology in the setting of maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection remains a topic of great interest because earlier studies have shown mixed results.

OBJECTIVE.—

To ascertain whether maternal SARS-CoV-2 infection is associated with any specific placental histopathology, and to evaluate the virus's propensity for direct placental involvement.

DESIGN.—

Placentas from 65 women with polymerase chain reaction-proven SARS-CoV-2 infection underwent histologic evaluation using Amsterdam consensus group criteria and terminology. Another 85 placentas from women without SARS-CoV-2 constituted the negative control group. A total of 64 of the placentas from the SARS-CoV-2-positive group underwent immunohistochemical staining for SARS-CoV-2 nucleocapsid protein.

RESULTS.—

Pathologic findings were divided into maternal vascular malperfusion, fetal vascular malperfusion, chronic inflammatory lesions, amniotic fluid infection sequence, increased perivillous fibrin, intervillous thrombi, increased subchorionic fibrin, meconium-laden macrophages (M-LMs) within fetal membranes, and chorangiosis. There was no statistically significant difference in prevalence of any specific placental histopathology between the SARS-CoV-2-positive and SARS-CoV-2-negative groups. There was no immunohistochemical evidence of SARS-CoV-2 virus in any of the 64 placentas that underwent staining for viral nucleocapsid protein.

CONCLUSIONS.—

Our study results and a literature review suggest that there is no characteristic histopathology in most placentas from women with SARS-CoV-2 infection. Likewise, direct placental involvement by SARS-CoV-2 is a rare event.

COVID and Animal Trials: A Systematic Review

Extensive work is being done to form targeted drugs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection; however, it is imperative to have a safe and effective vaccine against the same to win the war against this pandemic. For creating an efficacious vaccine, a proper animal model needs to be selected which can have an acceptable similarity of response as well as effects when administered to humans. For the present research, extensive search was conducted in MEDLINE and bioRxiv and medRxiv servers which were published in the English language from January 1, 2020, to August 20, 2020. Search terms included animal models, SARS-CoV-2, COVID-19, immune response against coronavirus, nonhuman primates, mice, ferrets, and macaques. In our study, creating an adequate immune response mimicking the response as in humans, as the endpoint, was considered as inclusion criterion while assessment of any additional therapies like safety as well as minimal tolerable dose using animal models as well as formation of adequate sample size of these models against COVID-19 was not considered. In our search, 163 articles were shortlisted, of them only 20 articles were finally included in our study which addressed to our inclusion and exclusion criterion. Our research articles focused on nonhuman primates, mice, hamsters, ferrets, cats, and dogs, with the main goal to investigate the role of animal models in the pathogenesis of COVID-19. It was evident in our research that animal models only mimic limited signs and symptoms experienced in COVID infection as compared to infections in humans. However, they are still essential to understand the pathogenesis, transmissibility of viral particles, and vaccine testing.

The Immunological Role of the Placenta in SARS-CoV-2 Infection-Viral Transmission, Immune Regulation, and Lactoferrin Activity

A pandemic of acute respiratory infections, due to a new type of coronavirus, can cause Severe Acute Respiratory Syndrome 2 (SARS-CoV-2) and has created the need for a better understanding of the clinical, epidemiological, and pathological features of COVID-19, especially in high-risk groups, such as pregnant women. Viral infections in pregnant women may have a much more severe course, and result in an increase in the rate of complications, including spontaneous abortion, stillbirth, and premature birth-which may cause long-term consequences in the offspring. In this review, we focus on the mother-fetal-placenta interface and its role in the potential transmission of SARS-CoV-2, including expression of viral receptors and proteases, placental pathology, and the presence of the virus in neonatal tissues and fluids. This review summarizes the current knowledge on the anti-viral activity of lactoferrin during viral infection in pregnant women, analyzes its role in the pathogenicity of pandemic virus particles, and describes the potential evidence for placental blocking/limiting of the transmission of the virus.

Association Between COVID-19 Pregnant Women Symptoms Severity and Placental Morphologic Features

Since the beginning of the pandemic, few papers describe the placenta’s morphological and morphometrical features in SARS-CoV-2–positive pregnant women. Alterations, such as low placental weight, accelerated villous maturation, decidual vasculopathy, infarcts, thrombosis of fetal placental vessels, and chronic histiocytic intervillositis (CHI), have been described.

Effects of SARS-CoV-2 infection on human reproduction

The worldwide infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) impacts human health and life on multiple levels. People infected with SARS-CoV-2 suffer from physical disorders and psychological distress. At present, no direct evidence indicates that SARS-CoV-2 negatively influences human reproduction, and the possibility that gametes and embryos are affected requires further investigation. To evaluate the potential effects of SARS-CoV-2 infection on human reproduction and fetal health, this review summarizes the basic and clinical research of SARS-CoV-2 on reproduction up to date, hoping to offer guidance and advice to people at reproductive age and provide clues for the prevention and treatment of associated diseases.

Immunothrombosis in COVID-19: Implications of Neutrophil Extracellular Traps

SARS-CoV-2 is a member of the family of coronaviruses associated with severe outbreaks of respiratory diseases in recent decades and is the causative agent of the COVID-19 pandemic. The recognition by and activation of the innate immune response recruits neutrophils, which, through their different mechanisms of action, form extracellular neutrophil traps, playing a role in infection control and trapping viral, bacterial, and fungal etiological agents. However, in patients with COVID-19, activation at the vascular level, combined with other cells and inflammatory mediators, leads to thrombotic events and disseminated intravascular coagulation, thus leading to a series of clinical manifestations in cerebrovascular, cardiac, pulmonary, and kidney disease while promoting severe disease and mortality. Previous studies of hospitalized patients with COVID-19 have shown that elevated levels of markers specific for NETs, such as free DNA, MPO, and H3Cit, are strongly associated with the total neutrophil count; with acute phase reactants that include CRP, D-dimer, lactate dehydrogenase, and interleukin secretion; and with an increased risk of severe COVID-19. This study analyzed the interactions between NETs and the activation pathways involved in immunothrombotic processes in patients with COVID-19.

Placenta histopathology in SARS-CoV-2 infection: analysis of a consecutive series and comparison with control cohorts

Infection by SARS-CoV-2 has been shown to involve a wide range of organs and tissues, leading to a kaleidoscope of clinical conditions. Within this spectrum, an involvement of the fetal-maternal unit could be expected, but, so far, the histopathological evaluation of placentas delivered by women with SARS-CoV-2 infection did not show distinct hallmarks. A consecutive series of 11 placentas, delivered by 10 women with COVID-19 admitted to our Obstetrics and Gynecology clinic have been investigated and compared to a control cohort of 58 pre-COVID-19 placentas and 28 placentas delivered by women who had a previous cesarean section. Four out of eleven placentas showed changes consistent with chronic villitis/villitis of unknown etiology (VUE), while in one case, chronic histiocytic intervillositis was diagnosed. Thrombo-hemorrhagic alterations were observed in a subset of cases. Compared to the control cohort, chronic villitis/VUE (p < 0.001), chronic deciduitis (p = 0.023), microvascular thrombosis (p = 0.003), presence of infarction areas (p = 0.047) and of accelerated villous maturation (p = 0.005) showed higher frequencies in placentas delivered by women with COVID-19. Chronic villitis/VUE (p = 0.003) and accelerated villous maturation (p = 0.019) remained statistically significant by restricting the analysis to placentas delivered after a previous cesarean section. The observed differences in terms of pathological findings could be consistent with SARS-CoV-2 pathogenesis, but just a subset of alterations remained statistically significant after adjusting for a previous cesarean section. A careful consideration of potential confounders is warranted in future studies exploring the relationship between COVID-19 and pregnancy.

Pregnant women with COVID-19: the placental involvement and consequences

SARS-CoV-2, the leading cause of COVID-19 pandemic, was detected for the first time in Wuhan. In this study, we investigated the potential undesirable maternal and feto-neonatal consequences of COVID-19, and the related pathophysiological alterations in mother, neonate, and especially in the placenta as a vital organ, were reviewed. Also, the possibility of vertical transmission of virus and placental abnormalities were evaluated. The pregnant women were a vulnerable population for COVID-19, and several obstetric consequences were reported following SARS-CoV-2 infection. The higher risk of abruption, preterm labor, maternal death, stillbirth, intrauterine growth restriction, and newborns with fetal distress were adverse pregnancy and perinatal outcomes of COVID-19. Despite the ACE2 expression on placental components was confirmed, there is no agreement on the mother-child vertical transmission of this virus. Therefore, feto-neonatal consequences might be associated with placental abnormalities. The placental abnormalities are characterized by feto-maternal vascular malperfusion. Additionally, these adverse consequences lead to early termination of pregnancy in some cases, mostly via cesarean section. The pregnant women screening, coordination between healthcare personnel and neonatal unit, and infected women quarantine may decrease the risk of maternal and neonatal death after delivery.

Term Human Placental Trophoblasts Express SARS-CoV-2 Entry Factors ACE2, TMPRSS2, and Furin

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has had a massive impact on human lives worldwide. While the airborne SARS-CoV-2 primarily affects the lungs, viremia is not uncommon. As placental trophoblasts are directly bathed in maternal blood, they are vulnerable to SARS-CoV-2. Intriguingly, the human fetus is largely spared from SARS-CoV-2 infection. We tested whether the human placenta expresses the main SARS-CoV-2 entry factors angiotensin-converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2), and furin and showed that ACE2 and TMPRSS2 are expressed in the trophoblast rather than in other placental villous cells. While furin is expressed in the main placental villous cell types, we surveyed, trophoblasts exhibit the highest expression. In line with the expression of these entry factors, we demonstrated that a SARS-CoV-2 pseudovirus could enter primary human trophoblasts. Mechanisms underlying placental defense against SARS-CoV-2 infection likely involve postentry processing, which may be germane for mitigating interventions against SARS-CoV-2.

IMPORTANCE Pregnant women worldwide have been affected by COVID-19. As the virus is commonly spread to various organs via the bloodstream and because human placental trophoblasts are directly bathed in maternal blood, feto-placental infection by SARS-CoV-2 seems likely. However, despite the heightened risk to pregnant women, thus far the transmission risk of COVID-19 to the feto-placental unit seems extremely low. This has been recently attributed to a negligible expression of SARS-CoV-2 entry factors in the human placenta. We therefore sought to explore the expression of the entry factors ACE2 and TMPRSS2 in the different cell types of human placental villi. Using a combination of transcriptome sequencing (RNA-seq), real-time quantitative PCR (RT-qPCR), in situ hybridization, and immunofluorescence, we found that trophoblasts, but not the other main villous cell types, express ACE2 and TMPRSS2, with a broad expression of furin. Correspondingly, we also showed that primary human trophoblasts are permissive to entry of SARS-CoV-2 pseudovirus particles.