When is the Tdap vaccine recommended during pregnancy?

• A. First trimester (0–13 weeks)
• B. Second trimester (14–26 weeks)
• C. Third trimester (27–36 weeks)
• D. Any time after delivery

Answer: (C)

The main idea is to protect the newborn from pertussis by boosting maternal antibodies that cross the placenta. The best timing to achieve this is late in pregnancy, specifically between 27 and 36 weeks gestation. Giving the Tdap vaccine during this window maximizes the transfer of protective antibodies to the baby so newborns have some protection against pertussis in the first months of life, when they are most at risk and not yet fully immunized.

If given earlier in pregnancy, antibody levels in the newborn may be lower by birth; after delivery, there’s no opportunity for placental antibody transfer, so protection wouldn’t help the newborn immediately. The vaccine is inactivated and considered safe during pregnancy, and it’s recommended in every pregnancy to provide maximum protection for the newborn with each new pregnancy.