Vertical Transmission of COVID-19
The risk of vertical transmission of COVID-19 appears to be low, although some cases of apparent asymptomatic neonatal infection have now been reported.
Albert Yan, MD Commentary:
The Lancet case series (Chen et al, Lancet: Feb 12, 2020) highlighted 9 pregnant mothers with COVID-19 pneumonia during the third trimester who subsequently delivered 9 healthy infants, none of whom had evidence in the infants, based on evaluation of throat swabs, cord blood, and amniotic fluid. Notably, breastmilk samples examined in 6 of the mothers were also negative for virus. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30360-3/fulltext
A small case series of 2 pregnant mothers with COVID-19 infection during the third trimester also showed no evidence of vertical transmission, with RT-PCR screening showing no evidence of virus in the neonates’ nasopharynx, cord blood, placenta, amniotic fluid, and maternal breastmilk. https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa226/5809260
The largest series (Schwartz et al, Archives of Pathology and Lab Med. In press.) involved 38 pregnant mothers with COVID-19, and none of these mothers had infants who showed evidence of COVID-19 on RT-PCR screening. Importantly, unlike with SARS-CoV and MERS where significant maternal mortality was noted, mothers with SARS-CoV2 all survived. https://www.archivesofpathology.org/doi/10.5858/arpa.2020-0901-SA
However, 2 more recent studies reported the possibility that 3 neonates while appearing healthy may be asymptomatically infected either from intrauterine or congenital exposure. In the first report (Deng et al, JAMA: March 26, 2020), a single neonate born to a 29 year old mother with COVID-19 pneumonia was healthy-appearing. However, the infant had evidence of elevated IgM (which does not cross the placenta) and IgG to COVID-19, as well as 5 negative COVID-19 RT-PCR nasopharyngeal swabs. https://jamanetwork.com/journals/jama/fullarticle/2763853 In the other series (Zeng et al, JAMA: March 26, 2020), 6 pregnant mothers with COVID-19 had 6 infants who all had elevated COVID-19 IgG, but 2 of these also had significant elevations of IgM. Neither of these reported on the presence of virus in cord blood, amniotic fluid, breastmilk, or placental tissues. https://jamanetwork.com/journals/jama/fullarticle/2763854
While more data are needed to understand the real risks of vertical transmission, thus far, the upshot of this is that vertical transmission of COVID-19 from infected mothers appears to be very low, and even if it does occur as documented by elevated COVID-19-specific IgM, vertical transmission has not been associated with symptomatic infection or detectable virus on nasopharyngeal swabs.