Pregnant women who are positive with COVID -19 when they give birth rarely transmit the virus to their newborns, according to a series of new research. The reason: COVID isn’t often found in a patient’s bloodstream. The Centers for Disease Control and Prevention (CDC) released a study in September 2021 that found the rate of transmission from mother to baby was under four per cent. Another study published last February that looked at data from more than 4,000 women estimates it's even lower - around just two per cent. “Analyses show that infection among infants born to women with COVID -19 was uncommon," said Kate Woodworth, a medical epidemiologist at the CDC. In the small number of newborns who do test positive at birth, the CDC said studies have found most infections to be mild or asymptomatic. The World Health Organization has reported similar findings.
Research indicates that this likely has to do with the lack of virus in an expecting mother’s bloodstream. SARS-CoV-2 isn’t often present in blood samples, indicating that it doesn’t usually enter an infected person’s bloodstream. In one peer-reviewed study, for example, just six per cent of patients who visited the emergency room with COVID -19 had the virus in their blood. “For COVID -19 to reach a pregnant womb, it has to circulate in the bloodstream, and because the virus is not an agent that circulates in the bloodstream very frequently, there are not going to be a lot of women whose uterus, placenta and baby are exposed to the virus,” said David Schwartz, a medical epidemiologist and pathologist. Other recent data suggest viral presence in blood may be linked to more serious disease. Schwartz’s recent work has focused on the adverse effects COVID can have on pregnancy. He emphasized that there are still many unknowns.
Flu vaccines are strongly recommended for pregnant women, not only because they protect expectant mothers from serious illness, but because antibodies from the vaccine can travel through the placenta to help boost babies’ immunity before they’re old enough to get the shot themselves. There’s evidence that the same positive effect can occur with COVID -19 antibodies, offering some level of protection against the virus. A peer-reviewed study from the journal Weill Cornell Medicine that analysed umbilical cord blood samples from more than 100 pregnant women during 2021 found that those who were vaccinated during pregnancy began to produce antibodies a few days after their first dose. Just over two weeks later, they began transferring what’s known as “passive immunity" to their babies. This means that even if an infant is unlikely to catch COVID -19 in the womb, it would have protection against the virus even after entering the world.
Even so, a pregnant woman with COVID risks serious illness which can also have negative health consequences for her newborn child even if the baby is born COVID -free. Recent studies have linked COVID -19 infection during pregnancy to both preterm labor and stillbirth. Schwartz and health experts from 12 different countries recently teamed up to analyse placental damage caused by the virus, called placentitis. Damage to the placenta could offer some explanation for why adverse fetal outcomes sometimes do occur, Schwartz and colleagues found in one study published last August.