At what stage of pregnancy is it recommended for women to receive the Tdap booster?

The recommendation for women to receive the Tdap booster during the 27-36 weeks of pregnancy is based on the need to provide optimal protection for both the mother and the newborn. This timing ensures that the mother has sufficient time to develop antibodies against tetanus, diphtheria, and pertussis, which can then be transferred to the fetus through the placenta.

Receiving the Tdap vaccine during this window helps maximize the transfer of antibodies to the baby, offering the newborn some immunity against whooping cough, which can be particularly severe in infants. Administering the vaccine in the third trimester helps to establish this passive immunity before the baby is born, reducing the risk of pertussis in the early months of life when the infant is most vulnerable.

Timing the booster earlier in pregnancy, such as in the first or second trimester, may not provide the same level of antibody transfer to the fetus as it is later in the third trimester, and receiving it just before delivery might not allow enough time for antibodies to be adequately passed to the baby. Thus, administering the Tdap booster during 27-36 weeks is the best practice for maternal and neonatal health.