Tdap vaccine not linked to preterm birth

Women who receive the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (Tdap) may not be at increased risk of preterm birth or other adverse birth outcomes, according to a new study in JAMA. The findings add to existing data on the safety of Tdap in pregnancy, which is recommended by the Advisory Committee on Immunization Practices.

In the retrospective, observational cohort study, administrative healthcare databases from 2 California Vaccine Safety Datalink sites were used to identify 123,494 women who had singleton pregnancies ending in a live birth between January 1, 2010 and November 15, 2012. Of them, 26,229 (21%) received Tdap during pregnancy. Cox regression was used for preterm delivery, while Poisson regression was used for the risks of small-for-gestational age (SGA), hypertensive disorders of pregnancy, and chorioamnionitis.

Overall, Tdap vaccination was not associated with increased risk of adverse birth outcomes. Incidence of preterm term delivery was 6.3% in vaccinated women and 7.8% in unvaccinated women (adjusted relative risk [RR], 1.03; 95% confidence index [CI], 0.97-1.09). Of the vaccinated women, 8.4% had SGA births, versus 8.3% of those who were unvaccinated (adjusted RR, 1.00; 95% CI, 0.96-1.06). Chorioamnionitis was diagnosed in 6.1% of vaccinated women and 5.5% of unvaccinated women (adjusted RR, 1.19; 95% CI, 1.13-1.26). In addition, administration of Tdap before 20 weeks’ gestation was not associated with development of a hypertensive disorder of pregnancy (adjusted RR, 1.09; 95% CI, 0.99-1.20).

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The researchers concluded that women who received Tdap vaccination while pregnant did not have an increased risk of preterm birth, hypertensive disorder in pregnancy, or SGA birth. There was, however, a small but statistically significant risk of chorioamnionitis.

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