If you don’t get the Tdap vaccine during pregnancy, your newborn will arrive without the borrowed antibodies that protect against whooping cough (pertussis) during the first two months of life, before they can receive their own vaccinations. This gap matters because whooping cough is most dangerous, and most likely to be fatal, in very young infants. Skipping the vaccine doesn’t guarantee your baby will get sick, but it removes a layer of protection during the window when your baby is most vulnerable.
How the Vaccine Protects Your Baby Before Birth
When you get Tdap during pregnancy, your immune system produces antibodies against pertussis, diphtheria, and tetanus. These antibodies cross the placenta through a receptor-based transport system, moving from your bloodstream into your baby’s circulation. This transfer begins in the first trimester but ramps up significantly in the third trimester. By 37 to 40 weeks, your baby’s antibody levels can actually match or exceed your own.
That’s why the CDC recommends getting Tdap between weeks 27 and 36 of each pregnancy, preferably on the earlier side of that window. Getting vaccinated earlier in the third trimester gives your body more time to build antibodies and transfer them before delivery. Getting it too late, past 36 weeks, may not leave enough time for full transfer, which could reduce how well your baby is protected.
What Your Baby Faces Without Those Antibodies
Babies can’t start their own pertussis vaccine series until they’re two months old, and they don’t build strong protection until they’ve had multiple doses. That leaves a vulnerable gap from birth to roughly four months. Whooping cough in young infants doesn’t always look like the classic “whoop.” It can cause prolonged coughing spells that make it hard for babies to breathe, turn their skin blue, or cause them to stop breathing entirely. Hospitalization is common, and some infants need intensive care.
A large cohort study found that maternal pertussis vaccination was associated with a 31% reduction in infant mortality. Babies born to vaccinated mothers had measurably lower odds of dying in infancy compared to babies whose mothers were not vaccinated. While pertussis-specific deaths are relatively rare in absolute numbers, the protection extends broadly, likely because the vaccine also prevents the cascade of complications that whooping cough triggers in tiny airways.
Cocooning Is Less Effective Than Vaccination During Pregnancy
Some parents consider an alternative strategy called “cocooning,” where everyone who will be around the baby (partner, grandparents, caregivers) gets vaccinated instead. This does help, but research from the American Academy of Pediatrics shows it’s significantly less effective than getting vaccinated during pregnancy.
Vaccination during pregnancy reduces infant pertussis cases by 33%, hospitalizations by 38%, and deaths by 49%. Postpartum cocooning, by contrast, reduces cases by only 20%, hospitalizations by 19%, and deaths by 16%. Even when cocooning includes a father and a grandparent in addition to the mother’s postpartum dose, it still doesn’t match the protection that prenatal vaccination provides. The reason is straightforward: cocooning reduces the chance that adults pass the infection to the baby, but it doesn’t give the baby any ability to fight the infection if exposed through other contact.
The Vaccine Does Not Increase Pregnancy Risks
If you’re hesitating because of safety concerns, the data on this is extensive and reassuring. A study of more than 118,000 pregnancies found no association between Tdap vaccination and preterm birth, with an adjusted hazard ratio of 1.01, meaning the risk was essentially identical whether or not the vaccine was given. There was also no increased risk of a uterine infection called chorioamnionitis, and no increase in adverse outcomes for infants.
These findings are consistent across multiple large studies. Tdap during pregnancy does not increase the risk of low birth weight, stillbirth, or birth defects. The most common side effects are the same ones anyone experiences: soreness at the injection site, mild fatigue, or a low-grade fever that resolves within a day or two.
What If You Missed the Window
If you’re past 36 weeks and haven’t received Tdap yet, getting it now is still better than not getting it at all. Antibody transfer will be reduced compared to vaccination at 28 or 30 weeks, but some protection will still cross the placenta before delivery. Your doctor can administer it at any point before your due date.
If you’ve already delivered without getting Tdap, you can still get vaccinated postpartum. This won’t transfer antibodies through the placenta, but it will reduce the chance that you contract whooping cough and pass it to your baby through close contact. You should also make sure that anyone spending time with your newborn is up to date on their Tdap, since cocooning becomes your primary strategy at that point.
If you’re breastfeeding, some antibodies do pass through breast milk, but the levels are much lower than what crosses the placenta during pregnancy. Breastfeeding alone is not a reliable substitute for prenatal vaccination when it comes to pertussis protection.
Why It’s Recommended Every Pregnancy
Even if you received Tdap during a previous pregnancy or had a booster a few years ago, the recommendation is to get it again during each pregnancy. Antibody levels decline over time, and the goal is to have your levels as high as possible during the third trimester so the maximum amount transfers to your baby. A dose you received two years ago will not produce the same peak of antibodies that a fresh dose during weeks 27 to 36 will generate. Each pregnancy, each baby, needs its own round of transferred protection to cover that vulnerable early window.