Receipt of the Tdap vaccine during pregnancy was not associated with increased risks for adverse birth outcomes in a safety study, although there was a weak association with chorioamnionitis.
In a separate study, tetanus, diphtheria, and pertussis coverage during pregnancy increased eightfold among women in five states in 2012, while dipping slightly in California.
©AvailableLight/iStockphoto.com
Receipt of the Tdap vaccine during pregnancy was not associated with increased risks for adverse birth outcomes in a safety study, although there was a weak association with chorioamnionitis.
The safety cohort included 26,224 women who received Tdap in pregnancy and 97,265 unvaccinated women with live births during 2010-2012 at two California sites in the Vaccine Safety Datalink (VSD) program.
Inpatient chorioamnionitis was diagnosed in 6.1% of vaccinated women and 5.5% of unvaccinated women (adjusted relative risk, 1.19; 95% confidence interval, 1.13-1.27), Dr. Elyse Olshen Kharbanda reported at the winter meeting of the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP).
In contrast, rates of preterm birth (less than 37 weeks’ gestation) were lower with receipt of Tdap (6.3% vs. 7.8%; hazard ratio, 0.88; 95% CI, 0.83-0.93), while rates were similar for small for gestational age births (8.4% vs. 8.3%; RR, 1.00; 95% CI, 0.96-1.06).
A new diagnosis of hypertensive disorders, examined only in those vaccinated before 20 weeks’ gestation, occurred in 8.2% of vaccinated and 8.0% of unvaccinated women (RR, 1.00; 95% CI, 0.99-1.20), she said.
Secondary analyses restricted to women vaccinated between 27 and 36 weeks’ gestation, consistent with the preferential timing for Tdap vaccination, appeared to confirm the results. Chorioamnionitis occurred in 5.6% of vaccinated and 5.5% of unvaccinated women (RR, 1.11; 95% CI, 1.03-1.21), preterm birth in 5.3% vs. 7.8% (HR, 0.83; 95% CI, 0.77-0.90), and small for gestational age births in 8.6% vs. 8.3% (RR, 1.03; 95% CI, 0.96-1.10).
"The chorioamnionitis findings merit further discussion and possibly further investigation," said Dr. Kharbanda of the HealthPartners Institute for Education and Research, Minneapolis.
The findings in the current study persisted after researchers adjusted for risk factors such as maternal age and comorbidities, although data were not available for many of the most important chorioamnionitis risk factors, she said. Dr. Kharbanda went on to say that the magnitude of the potential risk detected was small, the risk was largely attributable to differences in chorioamnionitis rates seen only for the year 2012, and that there was no associated risk for preterm birth.
Several ACIP representatives questioned the choice of chorioamnionitis as a safety outcome, including American College of Obstetricians and Gynecologists representative Dr. Laura Riley of Harvard Medical School, Boston, who said, "It’s probably one of the messiest diagnoses there is, and it’s really hard to make any sense out of what it really means."
Carol Hayes, MPH, a certified nurse-midwife and a representative from the American Nurses Association, suggested the data be stratified by gestational age at birth because chorioamnionitis is a link for preterm birth, adding "What made you pick chorioamnionitis? It’s such a bizarre thing to look at with a vaccine."
Dr. Kharbanda said chorioamnionitis previously had been studied in relation to trivalent inactivated influenza vaccine, where the risk was slightly increased among pregnant women (Obstet. Gynecol. 2013;1211:519-25). She acknowledged that their obstetrical consultant had also "brought up that in maternal-fetal medicine, often chorioamnionitis is on the pathway for preterm delivery, but not considered an outcome in itself. I think we were sort of trying to look at common diagnoses that occur in women, and it is a common diagnosis."
Tdap coverage
Tdap coverage estimates were based on pregnancies ending between Jan. 1, 2007, and Nov. 15, 2012 at seven sites in the VSD, a collaboration between the CDC and nine managed-care organizations. Among 371,539 live births from 2007 to 2012, overall, 9.5% of women received Tdap during pregnancy and 14.4% post partum. In 2012, the corresponding rates were 13.7% and 8.8%.
In Colorado, Minnesota, Oregon, Washington, and Wisconsin, 16% of women were vaccinated with Tdap during pregnancy in 2012, compared with 2.2% in 2011, Dr. Kharbanda said. Prepregnancy Tdap vaccination rates were 46% and 56.2%, respectively
The increase in Tdap coverage during pregnancy is likely in response to ACIP’s June 2011 recommendation that health care providers administer Tdap to pregnant women who had not previously been vaccinated, preferably after 20 weeks’ gestation, she said.
ACIP updated its guidelines again in October 2012 because of persistent increases in whooping cough in the United States, this time calling for Tdap administration during each pregnancy, irrespective of prior vaccination history, and preferably between 27 and 36 weeks’ gestation.