Why is the Tdap vaccination timing during pregnancy recommended?

• A. During the first trimester.
• B. During the second trimester only.
• C. Immediately after delivery.
• D. During each pregnancy between 27-36 weeks to maximize maternal antibody transfer.

Answer: (D)

Maximizing the transfer of maternal antibodies to the newborn is the key idea. Antibodies to pertussis produced by the mother after the Tdap shot are passed to the fetus through the placenta, and this transfer happens most efficiently in the late second and third trimesters. Vaccinating during 27 to 36 weeks gestation builds up high maternal antibody levels that are then transferred to the baby in time to provide protection during the first months of life, when pertussis can be most severe and the infant hasn’t yet started the DTaP vaccine series.

Vaccinating too early in pregnancy may result in waning antibody levels by the time of birth, while vaccinating after delivery cannot provide the newborn with passive protection at all. Therefore, giving Tdap in every pregnancy between 27 and 36 weeks optimizes the baby’s passive immunity during the critical early period.