Placental SARS-CoV-2 distribution correlates with level of tissue oxygenation in COVID-19-associated necrotizing histiocytic intervillositis/perivillous fibrin deposition.

INTRODUCTION: Recent evidence supports the - rare - occurrence of vertical transplacental SARS-CoV-2 transmission. We previously determined that placental expression of angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 receptor, and associated viral cell entry regulators is upregulated by hypoxia. In the present study, we utilized a clinically relevant model of SARS-CoV-2-associated chronic histiocytic intervillositis/massive perivillous fibrin deposition (CHIV/MPFVD) to test the hypothesis that placental hypoxia may facilitate placental SARS-CoV-2 infection. METHODS: We performed a comparative immunohistochemical and/or RNAscope in-situ hybridization analysis of carbonic anhydrase IX (CAIX, hypoxia marker), ACE2 and SARS-CoV-2 expression in free-floating versus fibrin-encased chorionic villi in a 20-weeks' gestation placenta with SARS-CoV-2-associated CHIV/MPVFD. RESULTS: The levels of CAIX and ACE2 immunoreactivity were significantly higher in trophoblastic cells of fibrin-encased villi than in those of free-floating villi, consistent with hypoxia-induced ACE2 upregulation. SARS-CoV-2 showed a similar preferential localization to trophoblastic cells of fibrin-encased villi. DISCUSSION: The localization of SARS-CoV-2 to hypoxic, fibrin-encased villi in this placenta with CHIV/MPVFD suggests placental infection and, therefore, transplacental SARS-CoV-2 transmission may be promoted by hypoxic conditions, mediated by ACE2 and similar hypoxia-sensitive viral cell entry mechanisms. Understanding of a causative link between placental hypoxia and SARS-CoV-2 transmittability may potentially lead to the development of alternative strategies for prevention of intrauterine COVID-19 transmission.

Morphometric Parameters of Placental Villi in Parturient Women with COVID-19.

We performed a comparative morphological analysis of placental villi in parturient women with mild and moderate COVID-19 infection. The area and perimeter of terminal villi, their capillaries, and syncytiotrophoblast were assessed on immunohistochemical preparations with antibodies to CD31 using an image analysis system; the parameters of fetal vascular component in the placental villi were also assessed. Changes in the studied parameters differed in parturient women with mild and moderate COVID-19 infection. The observed increase in the total perimeter with a simultaneous decrease in the total capillary area and the degree of vascularization of the placental villi in parturient women with COVID-19 indicates impairment of circulation in the fetal compartment and the development of placental hypoxia, which can be the cause of unfavorable neonatal outcomes.

SARS-CoV-2 can infect and propagate in human placenta explants.

The ongoing SARS-CoV-2 pandemic continues to lead to high morbidity and mortality. During pregnancy, severe maternal and neonatal outcomes and placental pathological changes have been described. We evaluate SARS-CoV-2 infection at the maternal-fetal interface using precision-cut slices (PCSs) of human placenta. Remarkably, exposure of placenta PCSs to SARS-CoV-2 leads to a full replication cycle with infectious virus release. Moreover, the susceptibility of placental tissue to SARS-CoV-2 replication relates to the expression levels of ACE2. Viral proteins and/or viral RNA are detected in syncytiotrophoblasts, cytotrophoblasts, villous stroma, and possibly Hofbauer cells. While SARS-CoV-2 infection of placenta PCSs does not cause a detectable cytotoxicity or a pro-inflammatory cytokine response, an upregulation of one order of magnitude of interferon type III transcripts is measured. In conclusion, our data demonstrate the capacity of SARS-CoV-2 to infect and propagate in human placenta and constitute a basis for further investigation of SARS-CoV-2 biology at the maternal-fetal interface.

Massive Perivillous Fibrin Deposition and Chronic Histiocytic Intervillositis a Complication of SARS-CoV-2 Infection.

An emerging complication of COVID-19 (SARS-CoV-2) infection is reported. A 23-year-old patient presented with high temperature and reduced fetal movements at 25 + 5/40 weeks of gestation. RT-PCR proved maternal COVID-19 infection. Ultrasound examination confirmed intrauterine death. Placenta histology showed necrosis of the villous trophoblast, associated with Chronic Histiocytic Intervillositis (CHI) and Massive Perivillous Fibrin Deposition (MPFD) with up to 90% - of the intervillous spaces being involved. Immunohistochemistry showed CD68 positive histiocytes in the intervillous spaces and the villous trophoblast was positive for the COVID-19 spike protein. RNA scope signal was indicative of the presence of the viral genome and active viral replication in the villous trophoblastic cells, respectively. MPFD is a gradually developing end-stage disease with various etiology, including autoimmune and alloimmune maternal response to antigens expressed at the feto-maternal interface and frequently accompanies chronic alloimmune villitis or histiocytic intervillositis. Covid-19 infection is associated with similar pattern of histological changes of the placenta leading to placental insufficiency and fetal death. This case report supports maternal- fetal vertical transmission of SARS-CoV-2 virus leading to placental insufficiency and fetal demise. MPFD and CHI appear to be the typical placental histology for SARS-CoV-2 virus infection associated fetal demise.

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.

Placental SARS-CoV-2 in a pregnant woman with mild COVID-19 disease.

The full impact of coronavirus disease 2019 (COVID-19) on pregnancy remains uncharacterized. Current literature suggests minimal maternal, fetal, and neonatal morbidity and mortality. COVID-19 manifestations appear similar between pregnant and nonpregnant women. We present a case of placental severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in a woman with mild COVID-19 disease, then review the literature. Reverse transcriptase polymerase chain reaction was performed to detect SARS-CoV-2. Immunohistochemistry staining was performed with specific monoclonal antibodies to detect SARS-CoV-2 antigen or to identify trophoblasts. A 29-year-old multigravida presented at 40-4/7 weeks for labor induction. With myalgias 2 days prior, she tested positive for SARS-CoV-2. We demonstrate maternal vascular malperfusion, with no fetal vascular malperfusion, as well as SARS-CoV-2 virus in chorionic villi endothelial cells, and also rarely in trophoblasts. To our knowledge, this is the first report of placental SARS-CoV-2 despite mild COVID-19 disease (no symptoms of COVID-19 aside from myalgias); patient had no fever, cough, or shortness of breath, but only myalgias and sick contacts. Despite her mild COVID-19 disease in pregnancy, we demonstrate placental vasculopathy and presence of SARS-CoV-2 virus across the placenta. Evidence of placental COVID-19 raises concern for placental vasculopathy (potentially leading to fetal growth restriction and other pregnancy complications) and possible vertical transmission-especially for pregnant women who may be exposed to COVID-19 in early pregnancy. This raises important questions of whether future pregnancy guidance should include stricter pandemic precautions, such as screening for a wider array of COVID-19 symptoms, increased antenatal surveillance, and possibly routine COVID-19 testing throughout pregnancy.

Chronic Histiocytic Intervillositis With Trophoblast Necrosis Is a Risk Factor Associated With Placental Infection From Coronavirus Disease 2019 (COVID-19) and Intrauterine Maternal-Fetal Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Transmission in Live-Born and Stillborn Infants.

CONTEXT.­: The number of neonates with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is increasing, and in a few there are reports of intrauterine infection. OBJECTIVE.­: To characterize the placental pathology findings in a preselected cohort of neonates infected by transplacental transmission arising from maternal infection with SARS-CoV-2, and to identify pathology risk factors for placental and fetal infection. DESIGN.­: Case-based retrospective analysis by a multinational group of 19 perinatal specialists of the placental pathology findings from 2 cohorts of infants delivered to mothers testing positive for SARS-CoV-2: live-born neonates infected via transplacental transmission who tested positive for SARS-CoV-2 after delivery and had SARS-CoV-2 identified in cells of the placental fetal compartment by molecular pathology, and stillborn infants with syncytiotrophoblast positive for SARS-CoV-2. RESULTS.­: In placentas from all 6 live-born neonates acquiring SARS-CoV-2 via transplacental transmission, the syncytiotrophoblast was positive for coronavirus using immunohistochemistry, RNA in situ hybridization, or both. All 6 placentas had chronic histiocytic intervillositis and necrosis of the syncytiotrophoblast. The 5 stillborn/terminated infants had placental pathology findings that were similar, including SARS-CoV-2 infection of the syncytiotrophoblast, chronic histiocytic intervillositis, and syncytiotrophoblast necrosis. CONCLUSIONS.­: Chronic histiocytic intervillositis together with syncytiotrophoblast necrosis accompanies SARS-CoV-2 infection of syncytiotrophoblast in live-born and stillborn infants. The coexistence of these 2 findings in all placentas from live-born infants acquiring their infection prior to delivery indicates that they constitute a pathology risk factor for transplacental fetal infection. Potential mechanisms of infection of the placenta and fetus with SARS-CoV-2, and potential future studies, are discussed.

Placental Pathology of COVID-19 with and without Fetal and Neonatal Infection: Trophoblast Necrosis and Chronic Histiocytic Intervillositis as Risk Factors for Transplacental Transmission of SARS-CoV-2.

The mechanism(s) by which neonates testing positive for coronavirus disease 2019 (COVID-19) acquire their infection has been largely unknown. Transmission of the etiological agent, SARS-CoV-2, from mother to infant has been suspected but has been difficult to confirm. This communication summarizes the spectrum of pathology findings from pregnant women with COVID-19 based upon the infection status of their infants and addresses the potential interpretation of these results in terms of the effects of SARS-CoV-2 on the placenta and the pathophysiology of maternal-fetal infection. Placentas from pregnant women with COVID-19 and uninfected neonates show significant variability in the spectrum of pathology findings. In contrast, placentas from infected maternal-neonatal dyads are characterized by the finding of mononuclear cell inflammation of the intervillous space, termed chronic histiocytic intervillositis, together with syncytiotrophoblast necrosis. These placentas show prominent positivity of syncytiotrophoblast by SARS-CoV-2, fulfilling the published criteria for transplacental viral transmission as confirmed in fetal cells through identification of viral antigens by immunohistochemistry or viral nucleic acid using RNA in situ hybridization. The co-occurrence of chronic histiocytic intervillositis and trophoblast necrosis appears to be a risk factor for placental infection with SARS-CoV-2 as well as for maternal-fetal viral transmission, and suggests a potential mechanism by which the coronavirus can breach the maternal-fetal interface.