At what gestational age should a pregnant woman receive the Tdap (tetanus, diphtheria, and pertussis) vaccine?

Tdap Vaccination Timing During Pregnancy

Pregnant women should receive Tdap vaccine between 27 and 36 weeks of gestation during every pregnancy, with vaccination earlier in this window (27-30 weeks) preferred to maximize passive antibody transfer to the infant. 1, 2

Optimal Timing and Rationale

The recommended window of 27-36 weeks gestation is based on several physiological factors:

• Active transport of maternal immunoglobulin G does not substantially occur before 30 weeks of gestation 1
• A minimum of 2 weeks is required after Tdap administration to mount a maximal immune response to vaccine antigens 1
• Women vaccinated during the first or second trimester have low antibody levels at term due to rapid antibody waning, making early vaccination ineffective for infant protection 1

Vaccinating earlier within the 27-36 week window produces superior outcomes:

• Infants whose mothers received Tdap at 27-32 weeks gestation have significantly higher antipertussis antibody concentrations in cord blood compared to those vaccinated after 32 weeks 1
• Maternal Tdap vaccination during the 27-36 week period is 80-91% effective in preventing infant pertussis 2
• Earlier vaccination within this window allows more time for antibody production and transplacental transfer before delivery 1, 3

Vaccination During Each Pregnancy

Tdap must be administered during every pregnancy, regardless of prior vaccination history:

• Antipertussis antibodies decay substantially within the first year after vaccination in healthy adults 1
• Women vaccinated before pregnancy have antibody levels that wane quickly and are unlikely to provide adequate passive protection to infants 1
• A single dose of Tdap during one pregnancy is insufficient to provide protection for subsequent pregnancies 1

Special Clinical Situations

For pregnant women requiring tetanus booster (>10 years since previous Td):

• Administer Tdap between 27-36 weeks gestation instead of Td 1, 2

For wound management during pregnancy:

• If ≥5 years have elapsed since the previous tetanus booster, administer Tdap regardless of gestational age 1, 2
• This takes precedence over the optimal timing window when wound management is indicated 1, 4

For pregnant women with unknown or incomplete tetanus vaccination:

• Administer a three-dose series (at 0,4 weeks, and 6-12 months) 1, 2
• Replace one dose with Tdap, preferably between 27-36 weeks gestation 1, 2

If Tdap is not administered during pregnancy:

• Give immediately postpartum, ideally before hospital discharge 1, 2, 5

Safety Profile

• Experience with tetanus toxoid-containing vaccines demonstrates no excess risk for severe adverse events when Tdap is given during subsequent pregnancies 1
• The potential benefit of preventing pertussis morbidity and mortality in infants outweighs theoretical concerns of possible adverse events 1
• Inactivated vaccines like Tdap are generally safe during pregnancy 2

Common Pitfalls to Avoid

Missing the optimal vaccination window:

• The 27-36 week window is critical; vaccination outside this period results in suboptimal antibody transfer 1, 2
• Do not delay vaccination beyond 36 weeks, as there may be insufficient time for antibody production and transfer before delivery 1

Failing to vaccinate during each pregnancy:

• Prior Tdap vaccination does not eliminate the need for vaccination in subsequent pregnancies due to rapid antibody waning 1, 5
• This is the most common error in clinical practice, with many providers incorrectly assuming prior vaccination provides adequate protection 6, 7

Delaying Tdap when indicated for wound management:

• Wound management takes priority over optimal timing; administer Tdap immediately when indicated regardless of gestational age 1, 4