Tetanus, diphtheria, and pertussis vaccine (Tdap) in pregnancy and risk of major birth defects in the offspring.

Background: The tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine is recommended during pregnancy to protect newborns against pertussis infection in the months prior to their primary pertussis vaccination. Although research on the safety of the vaccine has been reassuring, most previous studies have considered major malformations as a single outcome, and have not examined potential risks for specific malformations.

Methods: Using data from the Slone Epidemiology Center Birth Defects Study collected between 2006 and 2015, we identified exposures to Tdap vaccine in both early and late pregnancy and examined potential risks for specific malformations. We used logistic regression models to calculate propensity score-adjusted odds ratios (aORs) and 95% confidence intervals (CIs).

Results: We identified 2,357 women exposed to Tdap during pregnancy. For first trimester exposures, the risk estimate for malformations overall was 1.0 (0.7, 1.5). We had power to examine nine specific malformations and found adjusted odds ratios ranging from 0.7 to 1.3, none of which had confidence intervals that excluded 1.0. For second or third trimester exposures, we examined 15 malformations with potential late pregnancy etiology, and calculated adjusted risk estimates for nine of these. Risk estimates ranged from 0.5 to 1.9, with no lower confidence bounds that excluded 1.0.

Conclusions: We observed no evidence of appreciable risks for selected specific major malformations associated with Tdap vaccine exposure during early or late pregnancy. As pertussis remains a public health concern and Tdap vaccination levels in pregnancy remain below desired levels, these data provide further reassurance regarding the current recommendations for Tdap vaccination in pregnancy.