Congenital infection of SARS-CoV-2 appears to be exceptionally rare despite many cases of COVID-19 during pregnancy. Robust proof of placental infection requires demonstration of viral localization within placental tissue. Only two of the few cases of possible vertical transmission have demonstrated placental infection. None have shown placental expression of the ACE2 or TMPRSS2 protein, both required for viral infection. We examined 19 COVID-19 exposed placentas for histopathologic findings, and for expression of ACE2, and TMPRSS2 by immunohistochemistry. Direct placental SARS-CoV-2 expression was studied by two methods-nucleocapsid protein expression by immunohistochemistry, and RNA expression by in situ hybridization. ACE2 membranous expression in the syncytiotrophoblast (ST) of the chorionic villi is predominantly in a polarized pattern with expression highest on the stromal side of the ST. In addition, cytotrophoblast and extravillous trophoblast express ACE2. No ACE2 expression was detected in villous stroma, Hofbauer cells, or endothelial cells. TMPRSS2 expression was only present weakly in the villous endothelium and rarely in the ST. In 2 of 19 cases, SARS-CoV-2 RNA was present in the placenta focally in the ST and cytotrophoblast. There was no characteristic histopathology present in our cases including the two placental infections. We found that the placenta is capable of being infected but that this event is rare. We propose one explanation could be the polarized expression of ACE2 away from the maternal blood and pronounced paucity of TMPRSS2 expression in trophoblast.

The coronavirus disease 2019 (COVID-19) pandemic caused significant mortalities in the adult population in New York City. Pregnant women at late gestational age positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) showed mild symptoms compared with nonpregnant adults. Rare cases of newborn babies testing positive for the SARS-CoV-2 virus within the first 24 hours have been reported. 1,2 Miscarriages in second trimesters were also reported related to maternal COVID-19. 3 Placental pathology has been studied in small case series with controversial results, and vertical transmission was reported in some cases. 4e6 We sought to examine the placental pathology and to localize the SARS-CoV-2 viral particles within the placental tissue.

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