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.

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.

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.

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.  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.

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.