During which trimester is the Tdap vaccine typically administered to pregnant women?

The Tdap vaccine is recommended for pregnant women during the third trimester, ideally between 27 and 36 weeks of gestation. Administering the vaccine during this window maximizes the maternal antibody response and the transfer of these antibodies to the fetus, thus providing protection to the newborn against whooping cough in the early months of life. This timing takes advantage of the significant development of the fetus in the third trimester and helps ensure that the mother has an adequate immune response that can be passed on.

Giving the Tdap vaccine in postpartum or during other trimesters does not offer the same level of protection to the infant, as the antibodies will not be as effectively transferred to the baby before birth. Hence, the third trimester is emphasized as the most beneficial timeframe for both maternal and neonatal immunity.