Vaccinate women during each pregnancy preferably between 27-36 wks, regardless of previous Tdap admin
Immunity wanes 8 y after immunization.  Often elderly will get the disease and transmit it to young unimmunized infants.
Caveats
Adolescents who have already gotten a booster dose of Td are encouraged to get a dose of Tdap as well. Waiting 5 years after their last Td is encouraged but not required. A period of at least 2 years between Td and Tdap is recommended in these cases.
Pregnancy is not a contraindication to Tdap. The only true contraindication to tetanus immunization is a history of neurologic or severe hypersensitivity to a previous dose.
Stable neurologic disorders and family history of vaccine reactions are not contraindications to receiving these vaccines.
No vaccine has ever been shown to play any role in the development of autism or autism spectrum disorders.
Pertussis
Airway obstruction
Diphtheria
Anaphylaxis
Influenza
Angioedema
Poliomyelitis
Aspirated foreign body