COVID-19 Vaccination Does Not Increase Risk of Preterm Birth

Yesterday, the US Centers for Disease Control and Prevention (CDC) reported that COVID-19 vaccination has no correlation with preterm birth or small-for-gestational-age at birth.

COVID-19 vaccines have been recommended during pregnancy to prevent severe maternal and birth infection outcomes. Pregnant women are at increased risk of severe or fatal COVID-19 infection, and are more likely to need ICU admission, invasive ventilation, and machine-assisted blood oxygenation than nonpregnant people.

However, vaccination rates among pregnant women have been low, largely due to concerns that the vaccine could cause adverse effects in the mothers or their babies.

Prior studies of maternal COVID-19 vaccination and birth outcomes have been hindered by small sample sizes or a lack of an unvaccinated control group. A CDC-sponsored study evaluated risk of preterm birth and small-for-gestational-age (SGA) at birth after maternal COVID-19 vaccination.

The retrospective cohort study, published in the CDC’s Morbidity and Mortality Weekly Report (MMWR), utilized data from 8 Vaccine Safety Datalink (VSD) health organizations.

“Preterm birth” was defined as fewer than 37 weeks of gestation, and “SGA at birth” was defined as a birthweight less than the tenth percentile for gestational age.

The study included 46079 pregnant women with live births, 10064 (21.8%) of whom received one or more COVID-19 vaccine doses during their pregnancy and between December 15, 2020-July 22, 2021.

Almost all women (98.3%) were vaccinated during their second or third trimester. Up to 96% of the vaccinated mothers received an mRNA Pfizer-BioNTech or Moderna vaccine.

The investigators found that COVID-19 vaccination during pregnancy was not associated with preterm birth (adjusted hazard ratio [aHR] = 0.91; 95% CI = 0.82–1.01). Vaccination during pregnancy was also not associated with SGA at birth (aHR = 0.95; 95% CI = 0.87–1.03).

Notably, there was no increased risk when stratified by mRNA COVID-19 vaccine type, or by second or third trimester vaccination, as compared with risk among the unvaccinated pregnant cohort.

The CDC reified their recommendation that women who are pregnant, were recently pregnant and/or lactating, or are trying to become pregnant all receive a full COVID-19 vaccine regimen.