Pregnant women may be at higher risk of severe complications associated with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which may lead to obstetrical complications. We performed a case control study comparing pregnant women with severe coronavirus disease 19 (cases) to pregnant women with a milder form (controls) enrolled in the COVI-Preg international registry cohort between March 24 and July 26, 2020. Risk factors for severity, obstetrical and immediate neonatal outcomes were assessed. A total of 926 pregnant women with a positive test for SARS-CoV-2 were included, among which 92 (9.9%) presented with severe COVID-19 disease. Risk factors for severe maternal outcomes were pulmonary comorbidities [aOR 4.3, 95% CI 1.9–9.5], hypertensive disorders [aOR 2.7, 95% CI 1.0–7.0] and diabetes [aOR2.2, 95% CI 1.1–4.5]. Pregnant women with severe maternal outcomes were at higher risk of caesarean section [70.7% (n = 53/75)], preterm delivery [62.7% (n = 32/51)] and newborns requiring admission to the neonatal intensive care unit [41.3% (n = 31/75)]. In this study, several risk factors for developing severe complications of SARS-CoV-2 infection among pregnant women were identified including pulmonary comorbidities, hypertensive disorders and diabetes. Obstetrical and neonatal outcomes appear to be influenced by the severity of maternal disease.

Pregnant women have been carefully observed during the COVID-19 pandemic, as the pregnancy-specific immune adaptation is known to increase the risk for infections. Recent evidence indicates that even though most pregnant have a mild or asymptomatic course, a severe course of COVID-19 and a higher risk of progression to diseases have also been described, along with a heightened risk for pregnancy complications. Yet, vertical transmission of the virus is rare and the possibility of placental SARS-CoV-2 infection as a prerequisite for vertical transmission requires further studies. We here assessed the severity of COVID-19 and onset of neonatal infections in an observational study of women infected with SARS-CoV-2 during pregnancy. Our placental analyses showed a paucity of SARS-CoV-2 viral expression ex vivo in term placentae under acute infection. No viral placental expression was detectable in convalescent pregnant women. Inoculation of placental explants generated from placentas of non-infected women at birth with SARS-CoV-2 in vitro revealed inefficient SARS-CoV-2 replication in different types of placental tissues, which provides a rationale for the low ex vivo viral expression. We further detected specific SARS-CoV-2 T cell responses in pregnant women within a few days upon infection, which was undetectable in cord blood. Our present findings confirm that vertical transmission of SARS-CoV-2 is rare, likely due to the inefficient virus replication in placental tissues. Despite the predominantly benign course of infection in most mothers and negligible risk of vertical transmission, continuous vigilance on the consequences of COVID-19 during pregnancy is required, since the maternal immune activation in response to the SARS-CoV2 infection may have long-term consequences for children’s health.

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