Mother-to-Baby COVID-19 Transmission Likely Rare

New mothers with COVID-19 had a low chance of passing the infection on to their baby, according to a systematic review and meta-analysis.

In 472 studies that included over 14,000 babies born to mothers with SARS-CoV-2 infection, only 1.8% (95% CI 1.2-2.5) tested positive on an RT-PCR test, reported Shakila Thangaratinam, MD, PhD, of the University of Birmingham in England, and colleagues in The BMJ.

Of the 592 COVID-positive babies with data on the timing of exposure and type and timing of tests, 14 were confirmed to be cases of mother-to-infant transmission. Seven babies acquired infection in utero, two during childbirth, and five in the early postnatal period.

“We found evidence for confirmed mother-to-child-transmission through in utero, intrapartum, and early postnatal exposure,” the authors wrote. “But the overall risk is likely to be low.”

Of 800 COVID-positive babies with available data on neonatal outcomes, 20 were stillbirths, and 23 died, while 750 survived to the end of follow-up.

There were significant associations between maternal factors and risk of infection among infants, the researchers found. In an analysis of 22 studies including nearly 3,000 women, mothers with severe COVID-19 were more likely to have a baby who tested positive (OR 2.36, 95% CI 1.28-4.36).

Other risk factors associated with COVID-19 infection in offspring included maternal admission to the intensive care unit (OR 3.46, 95% CI 1.74-6.91), maternal death (OR 14.09, 95% CI 4.14-47.97), and postnatal maternal diagnosis of COVID-19 (OR 4.99, 95% CI 1.24-20.13).

SARS-CoV-2 positivity was not associated with trimester of maternal infection, preterm birth, mode of delivery, or separation of mother and baby after birth, the team noted.

“Although some important conclusions can be drawn from this review, the paucity of high quality data on risks to infants from COVID-19 is also highlighted,” wrote Catherine McLean Pirkle, PhD, of the University of Hawaii at Manoa in Honolulu, in an accompanying editorial.

“Given that vaccines are not available for babies and young children, it is critical that better data become available to inform appropriate shared decision making on perinatal care between parents and healthcare providers,” she added.

For this systematic review and meta-analysis, Thangaratinam and colleagues conducted database searches of studies evaluating maternal and infant COVID-19 infections from December 2019 to August 2021.

They analyzed 472 studies (28,952 mothers, 18,237 babies), including 206 cohort studies of pregnant and recently pregnant women who sought hospital care for any reason and had a diagnosis of COVID-19, as well as 266 case series and case reports to assess the timing and likelihood of mother-to-baby COVID-19 transmission among infants who tested positive. None of the studies were conducted during the emergence of any SARS-CoV-2 variants of concern.

Thangaratinam and colleagues noted that their study was limited by the heterogeneity of populations, tests, and outcomes. Additionally, because nearly all mothers in the study had a recent SARS-CoV-2 infection, the results are not applicable to those who were infected early in pregnancy and recovered. The type, timing, and accuracy of testing performed on babies also varied, they added.