Researchers found that infants whose mothers received Tdap immunization between 27 weeks' and 36 weeks' gestation had significantly higher geometric mean concentrations of pertussis toxin antibodies in their cord blood than those whose mothers weren't given Tdap vaccine, even after controlling for gestational age at delivery, ethnicity and maternal age. The findings in the Journal of the American Medical Association also showed that maternal Tdap administration during 27 weeks' to 30 weeks' gestation was associated with the highest GMCs of neonatal pertussis antibodies, which peaked at week 30.