In a pregnant patient, when is the TDAP vaccine recommended?

• A. 20-28 weeks
• B. 27-36 weeks
• C. 32-40 weeks
• D. 36-40 weeks

Answer: (B)

Vaccination during pregnancy aims to maximize the transfer of protective antibodies from mother to newborn, reducing pertussis risk in the infant’s first months. Antibody transfer across the placenta is strongest in the third trimester, so the best time to immunize is during a window when maternal antibodies can be produced and efficiently passed to the fetus. That window is roughly 27 to 36 weeks gestation. vaccinating earlier than 27 weeks risks waning antibody levels by delivery, while vaccinating after 36 weeks may not allow enough time for the maternal immune response and placental transfer to occur before birth. Therefore, the recommended timing is during this 27–36 week period, ideally within that window even if the mother has had prior Tdap. If vaccination isn’t given during pregnancy, it can be completed postpartum, but that won’t protect the newborn as effectively.