COVID-19 vaccination does not increase the risk of preterm birth

A study of more than 40,000 pregnant individuals has found that COVID-19 vaccination during pregnancy is not linked with a higher risk of preterm or small-for-gestational-age (SGA) births.

The study – reported by the Centers for Disease Control and Prevention (CDC) in the US – also found that the trimester when the vaccination was received, and number of doses received, did not increase these risks.

These findings support the safety of COVID-19 vaccination during pregnancy, which prevents severe illness in pregnant women, who have an increased risk of severe disease and death compared with the non-pregnant. They are also more likely to require admission to the intensive care unit, invasive ventilation, and machine-assisted blood oxygenation.

Research into reasons behind low vaccine acceptance among pregnant women have found that the most common concerns involve a lack of information about vaccine safety and potential harm to the fetus. But according to lead author Heather Lipkind, an associate professor at the Yale School of Medicine, the results of this study address both concerns.

“Getting vaccinated against COVID-19 is important for preventing severe illness in pregnant people,” says Lipkind. “With the increasing rates of COVID-19 in our community we are encouraging pregnant people to get vaccinated.”

Researchers used data from eight different health care organisations participating in the Vaccine Safety Datalink Project – a project established by the CDC to monitor vaccine safety – in a retrospective cohort study of vaccinated and unvaccinated pregnant women aged 16–49 years.

Nearly 22% of those reviewed received at least one vaccine dose during pregnancy, the vast majority during their second or third trimester. Almost 96% of the vaccinated received an mRNA vaccine developed by Pfizer-BioNTech or Moderna.

Researchers investigated the risk of preterm birth (babies delivered earlier than 37 weeks) and SGA (babies delivered smaller in size than normal for gestational age), which have both been associated with a higher risk for infant death or disability. There was no link found with vaccination status, dose number, or vaccination by trimester for the first (or only) vaccine dose.

These findings are a crucial addition to the few reports which have described outcomes of live births after COVID-19 vaccination in pregnancy.

The authors note that further evaluation of risk associated with vaccination in the first trimester is needed in future studies. Less than 2% of first-trimester vaccinations were observed in this study, due to the timing of vaccine availability and of births. Research is also needed for more recent pregnancies in women who have received a booster vaccine dose during pregnancy.

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