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Tdap Vaccine in Pregnancy Not Associated with Birth Defects

A new study has found no correlation between receiving the Tdap vaccine during pregnancy and birth defects.

Vaccines can play an important role in protecting pregnant women and their babies from illness; however, many women have been concerned about the potential for birth defects. Pregnant women may be able to breathe a sigh of relief as the results of a new retrospective study show that the tetanus, diphtheria, and pertussis (Tdap) vaccine is not associated with birth defects. The Tdap vaccine during pregnancy can, however, provide valuable immunity against pertussis to the newborn.

Mothers pass on their disease immunity to their babies during pregnancy, and so it is important that pregnant women get the most accurate information on health recommendations and exclusions during those key months. According to the Centers for Disease Control and Prevention (CDC), maternal vaccines can play an important role in ensuring a healthy pregnancy. While the CDC guidelines recommend that women receive some vaccines—such as the measles, mumps, rubella (MMR) shot–at least one month before pregnancy, inoculations such as the flu shot and the Tdap vaccine can play an important role in protecting babies against disease in the first months of life when administered during pregnancy.

The CDC notes that while tetanus and diphtheria are rare conditions in the United States today, pertussis, or whooping cough, is a dangerous lung infection that can be particularly life threatening in infants. Caused by Bordetella pertussis, pertussis a highly contagious condition marked by severe coughing fits and a “whooping” sound when sufferers inhale. The infection begins with one to two weeks of low-grade fever, cold symptoms, and a milder cough. Once pertussis progresses, the severe cough can last for as long as 10 weeks or more. Early treatment with antibiotics is important to prevent the infection from worsening. After three weeks, even with persisting symptoms, Bordetella pertussis are no longer found in the body and antibiotics are no longer effective. Although the United States has seen an initial decline in cases of whooping cough since the introduction of the vaccine, cases have been steadily rising since the 1980s.

About half of all babies with whooping cough will end up hospitalized, says the CDC, and the condition kills up to 20 babies each year. While doctors recommend that babies begin receiving a course of pertussis shots at 2 months of age, vaccination in women during their pregnancies can offer some immunity to babies. Many women still decline the vaccine. “Based on reports it seems that fears regarding vaccine safety are one of the main reasons women choose not to receive vaccinations during pregnancy,” explains study author Malini DeSilva, MD, MPH. “One report from Wisconsin showed that although more women received the Tdap vaccine after the US Advisory Committee on Immunization Practices’ recommendation to receive Tdap during every pregnancy between 27 and 36 weeks’ gestation was made in 2013, the percentage of pregnant women receiving this vaccine plateaued around 50%.”

In their recent study, published in the Journal of the American Medical Association, Dr. DeSilva and a team of researchers from the CDC and HealthPartners Institute in Minneapolis examined the safety of maternal Tdap vaccination. Their retrospective cohort study looked at babies born at seven sites in six states from January 1, 2007 to September 30, 2013, comparing the rate of structural birth defects prevalence between infants born to women who had received the Tdap shot during pregnancy and women who were unvaccinated. The researchers studied vaccinations occurring at 14 weeks, 27 to 36 weeks, and any time during gestation. A total of 324,463 live births were included in their investigation.

In their findings, the study authors found no link between maternal Tdap vaccination and birth defects, including microcephaly. The research was conducted in part to examine whether the increase in microcephaly rates in Brazil attributed to the Zika outbreak also had any correlation to the November 2014 start of the country’s maternal Tdap vaccination program. “Tdap vaccination is recommended to be received during every pregnancy and it is important to monitor the vaccine’s safety during pregnancy, including its impact on birth defects,” notes Dr. DeSilva. “With increased instances in the United States of Zika infection, which can cause microcephaly, it is important to have evidence that the Tdap vaccination does not cause microcephaly because coincidental occurrence of microcephaly may be observed after Tdap vaccination.”

The researchers’ conclusion on the safety of the Tdap vaccine supports the CDC recommendation that women receive the whooping cough shot during the third trimester of pregnancy. The antibodies produced two weeks following vaccination are passed from mothers to their unborn babies during pregnancy—as well as through breastfeeding after delivery–and help close the gap in protection between birth and the child’s first vaccination at 2 months of age.