Receiving the Tdap vaccine during pregnancy did not raise the risk of maternal hypertensive disorders, preterm birth, or small-for-gestational age infants in an observational study of 123,494 California pregnancies, according to a report published online November 11 in JAMA.
In response to recent outbreaks of pertussis, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommends that the Tdap vaccine be given to all pregnant women, preferably at 27-36 weeks’ gestation. However, specific data regarding possible adverse effects on mothers or children are “limited,” said Dr. Elyse O. Kharbanda of HealthPartners Institute for Education and Research, Minneapolis, and her associates.
To examine the issue, the investigators analyzed information from the Vaccine Safety Datalink regarding singleton pregnancies resulting in a live birth at two California sites during a 3-year period. A total of 26,229 (21%) of mothers received the Tdap vaccine during pregnancy, and the remaining 97,265 did not, although 46% of them had received Tdap prior to pregnancy.
The rates of preterm birth were 6.3% in vaccine-exposed pregnancies and 7.8% in nonexposed pregnancies, a nonsignificant difference. Similarly, the rates of SGA infants were nearly identical between the two study groups at 8.4% and 8.3%, respectively. And the rates of maternal hypertensive disorders – including gestational hypertension, hypertension in pregnancy not otherwise specified, preeclampsia, and eclampsia – were not significantly different at 8.2% and 8.0%, respectively, Dr. Kharbanda and her associates said (JAMA 2014 [doi:10.1001/jama.2014.14825]).
“We detected an increased risk of being diagnosed with chorioamnionitis following vaccination,” but that finding should be interpreted with caution because the magnitude of the risk was small, and it didn’t translate into increased risk of preterm delivery. This weak association may have been due to residual confounding, especially since the data could not be adjusted to account for important chorioamnionitis risk factors such as prolonged rupture of membranes, prolonged labor, or the presence of pathogens in the mother’s genital tract, the investigators noted.
This study was funded by the Centers for Disease Control and Prevention. Dr. Kharbanda reported having no financial disclosures; some of her associates reported ties to GlaxoSmithKline, Sanofi Pasteur, Pfizer, Merck, Novartis, Nuron Biotech, Protein Science, and MedImmune. Two associates are CDC employees.