Association of COVID-19 vaccination before 12 weeks of gestation with ultrasound-detected congenital anomalies compared with later or no vaccination: A registry-based cohort study

Objective Our objective was to evaluate the occurrence of congenital anomalies in pregnant women who received at least one dose of COVID-19 vaccine from conception up to 11 w and 6 d in comparison to those vaccinated after 12 weeks of pregnancy or not vaccinated at all. Methods This study is a Registry-Based Cohort Study carried out in the cities of Yasuj and Hormozgan, Iran. Participants involved divided into three groups for analysis: unvaccinated individuals, vaccinated during the teratogenic window (defined as women who received at least one dose of COVID-19 vaccine from conception up to 11 w and 6 d ) and participants who received the vaccine after the first 12 weeks of pregnancy, (categorized as women vaccinated outside the organogenesis period). The primary outcome was congenital anomalies, which were identified as the presence of at least one birth defect detected prenatally through ultrasound. Results Overall, most congenital anomalies were rare and occurred at very low frequencies across groups. Atrioventricular septal defects (AVSD) were observed more frequently in women vaccinated within the teratogenic window compared with unvaccinated women (SMD = 0.22). Cleft palate also occurred slightly more frequently in this group (SMD = 0.13). For all other anomalies, effect sizes were small (SMD < 0.15) and no clinically meaningful differences were observed. Conclusion This study provides preliminary descriptive evidence regarding the occurrence of congenital anomalies following COVID-19 vaccination during early pregnancy. Because of the low number of events and the exploratory nature of the analyses, no causal inference can be made.