Tdap vaccine best given at 28-32 weeks pregnant

By Eva Martin, MD of Elm Tree Medical, Inc.

In the first months of life, newborns rely on their mothers’ immune systems to protect them from infections like pertussis. Pertussis infection, known as whooping cough, has become more common in infants who are too young to be vaccinated and thus protected against the illness. For these infants, their best defense is the Tdap vaccine given during the third trimester of pregnancy. Given the rising incidence of pertussis in newborns, OBGYNs have become interested to know exactly when during pregnancy is the best time to give the Tdap vaccine.

Researchers at the Monash University and Monash Health in Australia completed a study to answer this very question. 154 pregnant women participated in their study. They each belonged to one of three groups. One group received the Tdap vaccine between 28-32 weeks gestational age, which was considered the “early” third trimester group. The second group received the Tdap vaccine between 33-36 weeks, considered the “late” third trimester group. The third and final group did not receive the vaccine.

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The researchers collected samples of blood from the mothers before vaccination and cord blood from the infants at birth to measure their pertussis antibody levels. Compared to women who were unvaccinated in pregnancy, vaccinated women had infants with significantly higher antibody levels to pertussis. So which vaccination timing resulted in higher antibody levels? Early third trimester, between 28 and 32 weeks gestational age, resulted in higher antibody levels in cord blood. The researchers took their statistical analysis one step further and controlled for mothers’ baseline antibody levels before vaccination. In this case, there was a nonsignificant trend towards higher cord blood antibody levels with early vaccination.

The results of this study reinforce the importance of vaccination with Tdap during the third trimester of every pregnancy. And, to optimize the timing of the vaccination, targeting 28 to 32 weeks may lead to the best antibody protection for infants. We want to hear from you! At what gestational age do you usually recommend Tdap vaccine? Do pregnant women have a preference for when they receive the vaccine?