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Overall, Tdap shot safe for mom and baby, study finds

The Tdap shot - which protects against pertussis - is not associated with preterm birth, small birth weight, or hypertensive disorders of pregnancy, according to a new study.
The Tdap shot - which protects against pertussis - is not associated with preterm birth, small birth weight, or hypertensive disorders of pregnancy, according to a new study.
Photo by mahalie stackpole via Flickr Creative Commons

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As loyal readers of this Impatient blog know well, a whooping cough epidemic swept across the Golden State this year.

Infants too young to be vaccinated are most vulnerable to this disease, also known as pertussis. So to protect them, the state health department, as well as the Advisory Committee on Immunization Practices (the group that develops vaccine recommendations for the country) and the American College of Obstetricians and Gynecologists recently began recommending that all pregnant women in their third trimester get the Tdap shot, which protects against pertussis, as well as diphtheria and tetanus.

This new strategy allows moms to pass antibodies onto their babies, protecting the infants until they're old enough to get vaccinated.

But as a new article in the Journal of American Medicine explains, there has been limited data on whether Tdap vaccination during pregnancy affects the health of mothers or their babies… until now.

The study

As part of a JAMA study published this week, researchers analyzed administrative and electronic health record data of more than 123,000 California women -- 21 percent of whom received the Tdap shot during pregnancy between Jan. 1, 2010 and Nov. 15, 2012.

Among their findings:

The one finding that raises an eyebrow:

Still, "it is safe"

The authors describe these chorioamnionitis findings as "small but statistically significant."

They elaborate: "These results should be interpreted with caution because the magnitude of this risk was small, and we did not observe an increased risk of preterm birth," (which, they say, is often a consequence of chorioamnionitis.)

What does that mean to doctors?

"This study confirms the thoughts that we have had as a community of OBGYNs regarding giving the Tdap vaccination in pregnancy - specifically that it is safe and is not associated with adverse outcomes," Dr. Erica Oberman, a professor of obstetrics and gynecology at UCLA's David Geffen School of Medicine, said in an e-mail.

She added that more research could help explain this finding: "The article also does not discuss if there were other risk factors in the group of women that could have made them more susceptible to getting chorioamnionitis during their labor course - which would be an important piece of information," she said.

Jacqueline Guerrero, a professor of obstetrics and gynecology at UC Irvine Medical Center, agreed that this finding - the slightly increased risk for chorioamnionitis - shouldn't be a reason to stop administering Tdap to pregnant women in their third trimester.

"This slightly increased risk of chorioamnionitis is outweighed by the proven benefit of Tdap," she wrote, especially given that pertussis can be deadly for infants.

During this year's epidemic, many California mothers didn't follow these vaccination recommendations. The state knows the vaccination history for 158 – or 48 percent – of whooping cough cases in kids younger than four months old. Of those, 143 moms – or 77 percent – did not receive the Tdap shot during their third trimester.

Moms, did you receive the Tdap booster shot during pregnancy? What other questions do you have about this shot?