First trimester mRNA COVID-19 vaccination and risk of congenital malformation: a prospective observational Embryotox...

This observational cohort study evaluates the risk of major birth defects after maternal mRNA COVID-19 vaccination in the first trimester of pregnancy.

Outcomes of prospectively ascertained pregnancies with at least one mRNA COVID-19 vaccination in the first trimester (gestational week 2 + 0 to 12 + 6) were compared with a cohort of unvaccinated pregnant women of the same period, whose data were collected using the same approach. The enrolment of study cases was conducted over a period of 21 months. For inclusion in the study, a structured pregnancy follow-up had to be completed afterwards. The reported congenital anomalies were classified according to EUROCAT. Relevant maternal characteristics were considered and adjusted ORs were calculated using logistic regression.

The exposed study cohort included 1828 pregnant women who were vaccinated with an mRNA vaccine in the first trimester. The unexposed comparison cohort consisted of 1955 pregnant women. Sixty-eight major congenital malformations have been observed in the vaccinated and 53 in the unexposed cohort (3.86% vs. 3.09%). The analysis resulted in an adjusted OR of 1.30 (95% CI: 0.90-1.86). A wide range of performed sensitivity analyses was in line with this finding.

We did not detect a statistically significant increase in the overall birth defect rate after maternal mRNA COVID-19 vaccination in the first trimester.