Fewer than 2% of babies born to mothers with SARS-CoV-2 test positive at birth – but severity of infection is a factor, according to the latest analysis.
An international team of researchers reviewed nearly 500 studies, mainly from Europe, Central Asia and North America, involving 28,952 mothers with COVID-19 who sought hospital care for any reason, to assess rates of positivity among babies born to mothers with the virus.
They also examined the likely timing of mother-to-baby transmission, outcomes among babies with the virus, and whether factors associated with labour, delivery, or breastfeeding increased the risk of babies becoming infected.
The findings are published by The BMJ today.
The researchers found that 1.8% of the 14,271 babies born to mothers with SARS-CoV-2 infection also tested positive with a PCR test. This fell to 1% when analyses were limited to babies exposed to the virus before or during birth.
Of the 592 positive babies with data on the timing of exposure and type and timing of tests, 14 had confirmed mother-to-child transmission, of whom seven were in utero, two during labour or delivery, and five during the early postnatal period.
Out of the 800 positive babies with outcome data, 20 were stillbirths, 23 were neonatal deaths and eight were early pregnancy losses; 749 babies were alive at the end of follow-up.
The researchers, led by experts from the University of Birmingham, UK, found that babies were more likely to test positive for COVID-19 if their mothers had severe infection, were admitted to an intensive care unit, developed an infection, or died shortly after giving birth.
But they found no associations between a positive test in babies and the stage of pregnancy when the mother was infected, preterm birth, mode of delivery, breastfeeding, or mother-baby separation at birth.
Positivity rates varied between regions, ranging from 0.1% in studies from North America to 5.7% in studies from Latin America and the Caribbean.
Although there were some limitations that may have affected their results, including differences in definitions of severe and mild COVID-19 as well as the types, timing and accuracy of tests used, the team says their extensive analyses enabled them to assess the robustness of their findings according to the timing of maternal infection and testing in babies, and across regions.
“The overall rates of SARS-CoV-2 positivity in babies born to mothers with SARS-CoV-2 infection is low,” they conclude, adding that it is important to consider the changing landscape of the COVID-19 pandemic “including the prevalence of COVID-19 in various regions, the impact of vaccination, and the effects of known and emerging SARS-CoV-2 variants on mother-to-child transmission”.
Allotey J, Chatterjee S, Kew T et al. SARS-CoV-2 positivity in offspring and timing of mother-to-child transmission: living systematic review and meta-analysis. BMJ 17 March 2022; doi.org/10.1136/bmj-2021-067696
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