COVID-19 vaccine safe to administer in first trimester of pregnancy, study says

Among pregnant women, exposure to mRNA COVID-19 vaccine in the first trimester does not appear to contribute to an increased risk of selected major structural birth defects, according to a retrospective study.

Researchers used data from eight health systems in California, Oregon, Washington, Colorado, Minnesota, and Wisconsin in the Vaccine Safety Datalink. They looked at 42,156 eligible pregnancies (mean maternal age 30.9 years), of which 7,632 (18.1 percent) were exposed to an mRNA COVID-19 vaccine in the first trimester. Electronic health data using validated algorithms were used to identify selected major structural birth defects among live-born infants.

In the 34,524 pregnancies without exposure to a first-trimester COVID-19 vaccination, vaccine exposure occurred before pregnancy in 2,045 (5.9 percent) or during the second or third trimester in 13,494 (39.1 percent); 18,985 (55.0 percent) remained unvaccinated before or during pregnancy.

Compared with pregnant women who were unvaccinated in the first trimester, those who did receive the vaccine during the same period tended to be older (mean age 32.3 vs 30.6 years). Application of stabilized inverse probability weighting made the differences in baseline characteristics between vaccinated and unvaccinated pregnant persons in the first trimester negligible (standardized mean difference <0.20).

Selected major structural birth defects occurred in 113 infants (1.48 percent) born to mothers with exposure to first-trimester mRNA COVID-19 vaccination and in 488 infants (1.41 percent) born to mothers without first-trimester vaccine exposure (adjusted prevalence ratio, 1.02, 95 percent confidence interval, 0.78–1.33).

In secondary analyses, wherein major structural birth defect outcomes were grouped by organ system, no significant differences were observed between the first-trimester vaccinated and unvaccinated cohorts.