Tdap vaccination during pregnancy not associated with increased risk of preterm delivery

Among approximately 26,000 women, receipt of the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine during pregnancy was not associated with increased risk of preterm delivery or small-for-gestational-age birth or with hypertensive disorders of pregnancy, although a small increased risk of being diagnosed with chorioamnionitis (an inflammation of the membranes that surround the fetus) was observed, according to a study in the November 12 issue of JAMA.

The Tdap vaccine was licensed in 2005 for use in nonpregnant adolescents and adults. Initially, postpartum administration of Tdap to parents and other caregivers was encouraged to prevent the transmission of pertussis to newborns. However, recent outbreaks, including infant deaths, have led to changing Tdap vaccine recommendations. In 2010, California became the first state to recommend Tdap be routinely administered during pregnancy. Tdap is now recommended by the Advisory Committee on Immunization Practices for all pregnant women, preferably between 27 and 36 weeks' gestation. To date, there have been limited specific data on whether vaccination with Tdap during pregnancy adversely affects the health of mothers or their offspring, according to background information in the article.

Elyse O. Kharbanda, M.D., M.P.H., of the HealthPartners Institute for Education and Research, Minneapolis, and colleagues used administrative health care databases from 2 California Vaccine Safety Datalink sites to examine whether receipt of Tdap during pregnancy was associated with increased risks of selected adverse obstetric or birth outcomes. Included in the analysis were 123,494 women with pregnancies ending in a live birth between January 1, 2010 and November 15, 2012; 26,229 (21 percent) received Tdap during pregnancy and 97,265 did not.

The researchers found that receipt of Tdap during pregnancy was not associated with increased risk of preterm (<37 weeks' gestation) or small-for-gestational-age (SGA) births. Among all pregnancies, 8.4 percent of those who received Tdap during pregnancy and 8.3 percent who were unexposed to the vaccine had an SGA birth. The rate of preterm delivery among women receiving Tdap during pregnancy at 36 weeks' gestation or earlier was 6.3 percent, whereas the rate for unexposed women was 7.8 percent. Receipt of Tdap was not associated with increased risk of hypertensive disorders of pregnancy.

Among women who received Tdap at any time during pregnancy, 6.1 percent were diagnosed with chorioamnionitis compared with 5.5 percent of unexposed women. In the subset of women vaccinated between 27 and 36 weeks' gestation, this risk was still increased but less so. The authors note that these results should be interpreted with caution because the magnitude of the risk was small.

"Given limited prior safety data, continued widespread pertussis transmission, and current recommendations to routinely vaccinate during pregnancy, our study provides important information on the safety of Tdap vaccination during pregnancy," the authors write.