Pregnant women with COVID-19 appear to generally experience a mild clinical course and have similar risks of developing a severe case of the illness to the non-pregnant population. However, they are nevertheless considered a vulnerable group within the COVID-19 pandemic. Viral transmission from infected mothers to the newborns is, if possible, rare, and there is no need to refrain from breastfeeding; on the contrary, it is widely recommended.
Seroprevalence, clinical presentation and viral transmission to newborns
Studies in hospitals from around the world with implemented universal PCR testing on pregnant women admitted for delivery have shown different degrees of prevalence of COVID-19 among asymptomatic obstetric patients in cities such as Seattle (<1.5%), Connecticut (<3%), Tokyo (3.8%), New York (13.5%) or Wuhan (26.7%). While this might reflect local epidemic and transmission dynamics, factors related to differences within studies from single centers and different countries cannot be discarded.
Our own research, included in the Kids Corona project, from three referral hospitals in Barcelona has evaluated the seroprevalence and clinical presentation of COVID-19 in 874 cases of pregnant women in the first and third trimester. The results showed that 14% of pregnant women have antibodies against SARS-CoV-2, a substantially larger proportion than the present rates of PCR positive cases reported for women aged between 20 and 40 years in Barcelona (0.78%), and most developed the infection asymptomatically or with mild symptoms. Although the susceptibility to infection seemed to be the same in the first or third trimesters of gestation, the few pregnant women with more severe symptoms were those who contracted the infection during the third trimester, which is in line with other studies and similar to other respiratory viruses. These data show a reduced number of cases requiring critical care than those previously found by PCR testing (10%) and highlight the value of seroprevalence studies to capture the high proportion of asymptomatic or mild infections.
Although there have been few reported cases of positive infants born from mothers with COVID-19, confirmation of vertical transmission is challenging as it requires proper sampling and analysis of key tissues and fluids during and after delivery as well as rigorous protocols to effectively prevent postnatal (horizontal) transmission. Research to date suggests that, even if possible, vertical transmission can be considered uncommon.