Risk not increased when results stratified by vaccination in second or third trimester, mRNA COVID-19 vaccine dose

COVID-19 vaccination in pregnancy is not associated with preterm birth or small for gestational age (SGA) at birth, according to research published in the Jan. 4 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Heather S. Lipkind, M.D., from Yale University in New Haven, Connecticut, and colleagues compared the risks for preterm birth and SGA at birth among vaccinated and unvaccinated pregnant women with single-gestation pregnancies with an estimated start or last menstrual period during May 17 to Oct. 24, 2020. Data were included for 46,079 pregnant women with live births, of whom 21.8 percent received one or more COVID-19 vaccine dose during pregnancy; 98.3 percent were vaccinated during the second or third trimester.

The researchers observed no association between COVID-19 vaccination during pregnancy and preterm birth (adjusted hazard ratio, 0.91; 95 percent confidence interval, 0.82 to 1.01). COVID-19 vaccination in pregnancy was not associated with SGA among the 40,627 live births with birth weight available (adjusted hazard ratio, 0.95; 95 percent confidence interval, 0.87 to 1.03). Risk was not increased when results were stratified by mRNA COVID-19 vaccine dose or by second- or third-trimester vaccination compared with risk among unvaccinated pregnant women. The adjusted hazard ratios for first-trimester vaccination could not be calculated due to the small number of first-trimester exposures.

"The findings from this retrospective, multisite cohort of a large and diverse population with comprehensive data on vaccination, comorbidities, and birth outcomes add to the evidence supporting the safety of COVID-19 vaccination during pregnancy," the authors write.