SARS-CoV-2 and the role of vertical transmission from infected pregnant
women to their fetuses: systematic review
Abstract
Background Vertical transmission of SARS-CoV-2 has been reported but
appears uncommon. Objectives This study systematically reviewed the
evidence on vertical transmission of SARS-CoV-2 from pregnant women to
their neonates. Search strategy Literature searches in WHO Covid-19
Database, LitCovid, medRxiv, and Google Scholar for SARS-CoV-2 using
keywords and associated synonyms, search date to 20 December 2020; no
language restrictions. Selection criteria Studies of any design
reporting transmission. Data collection and analysis Two reviewers
independently assessed article eligibility and extracted data. Results
were reported descriptively; no meta-analyses were possible. Main
results 106 studies were included: 40 reviews and 66 primary studies,
most conducted in hospitals. 32 case reports were assessed as high risk
of bias, due to the study design; across the 34 remaining primary
studies, risk of bias was low to moderate. Sixteen case reports
described vertical transmission. In cohort studies and case series,
65/2391 (2.7%) neonates born to mothers with a COVID-19 diagnosis
tested positive for SARS-CoV-2 within 24 hours of birth; the proportion
of positive neonates ranged from 0% to 22%. Twenty studies reported no
vertical transmission. Maternal symptomatology and mode of delivery were
not correlated with vertical transmission. 7/25 studies of placental
tissue identified SARS-CoV-2; vertical transmission was infrequent. No
study reported the results of viral culture to detect SARS-CoV-2.
Conclusions These findings indicate that vertical transmission is
possible, but not frequent. Further high-quality studies are needed to
understand vertical transmission. Funding World Health Organization: WHO
registration No 2020/1077093.