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

From the very beginning, special attention regarding severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and the resulting coronavirus disease-2019 (COVID-19) has been paid to pregnant women. In this review, after a short introduction into the immunodefensive role of the placenta and viral infections in general, we describe the morphological changes of the placenta in SARS-CoV-2-infected pregnant women based on our own and other published studies, draw comparisons to the SARS epidemic, and discuss the question of vertical transmission of SARS-CoV-2 from the mother to the neonate. The most common pathological findings of the placenta in SARS-CoV-2 infection are signs of maternal and fetal malperfusion as well as potentially immunologically and/or thromboinflammation-mediated findings. These manifest as infarcts and decidual vasculopathy as well as thrombi in the fetal circulation and avascular villi. In some cases, there is also an inflammatory reaction with villitis, intervillositis, and fetal vasculitis. In addition, it has been shown that SARS-CoV-2 can directly infect the placenta, so vertical transmission is possible. There is no COVID-19 specific pattern of placental alterations, although the detection of fetal thrombovasculitis, villitis, and intervillositis as well as fetal and maternal malperfusion could be best interpreted as the signature of SARS-CoV-2 infection - considering the known pathophysiology of COVID-19 regarding other organs (inflammatory reaction and [micro]angiopathy). Detection of viral RNA in the fetal placental tissue and the umbilical cord indicates SARS-CoV-2 vertical transmission.