Protecting Baby or Taking a Risk? Unpacking the Tdap Vaccine in Pregnancy

As a pediatrician, my focus is primarily on caring for children from birth through adolescence—but over the past few years, I’ve noticed a growing number of questions from expectant parents about medical decisions made during pregnancy, especially around vaccinations. One of the most common topics that comes up is the Tdap vaccine. Though I don't administer vaccines to pregnant women myself, I often help families navigate these decisions by reviewing the research and offering context. Given how frequently this question arises, I wanted to pull together an overview of the evidence, the rationale behind the recommendation, and the ongoing questions that many thoughtful parents are asking.

TDaP

One of the most routinely recommended vaccines during pregnancy is, as mentioned the Tdap—short for tetanus, diphtheria, and acellular pertussis. It’s a combination vaccine that protects against three bacterial infections:

· Tetanus: A serious infection caused by Clostridium tetani bacteria, often found in soil or dust. It can enter the body through wounds and cause severe muscle spasms.

· Diphtheria: A respiratory infection that was once a major cause of childhood illness and death. It’s now rare due to widespread vaccination but still present in some regions.

· Pertussis (whooping cough): A highly contagious respiratory disease that causes severe coughing fits, which can be life-threatening for newborns.

The primary reason Tdap is offered in pregnancy—typically between 27 and 36 weeks gestation—is to provide passive immunity to the baby. The idea is to pass maternal antibodies through the placenta to help protect the baby during the first vulnerable months of life.

The emphasis is especially strong from the CDC for pertussis, as whooping cough has led to severe complications and even deaths in newborn and young babies.

But as with many modern interventions, questions remain—about necessity, timing, risk, and whether a one-size-fits-all approach makes sense in today’s nuanced health landscape.

In the following sections, we’ll explore what the research says, examine emerging concerns, and unpack the decision-making process for parents who want to understand more than just the recommendation.

Why Pertussis Is the Focus of the Tdap Vaccine in Pregnancy

When we talk about the Tdap vaccine in pregnancy, the main reason it’s offered is to protect against pertussis, more commonly known as whooping cough. While Tdap also includes protection against tetanus and diphtheria, it’s the pertussis component that drives the recommendation during pregnancy. Whooping cough is a highly contagious bacterial illness that can be especially dangerous for infants. In the United States, the CDC reports anywhere from 10,000 to 20,000 cases of pertussis annually, though actual numbers may be higher due to underreporting. Among infants under 6 months who contract pertussis, roughly 50% require hospitalization. Of those hospitalized, about 1 in 5 develop pneumonia, and tragically, around 1% of infected infants die from complications. The concern is particularly acute in the first few months of life, before babies are offered their primary DTaP series—hence the push to give pregnant women Tdap during the third trimester, so maternal antibodies can pass to the baby and offer some early protection.

Effectiveness in Infants

The Tdap vaccine, when administered during pregnancy—typically between 27 and 36 weeks—has been shown to provide meaningful protection to infants during their most vulnerable early months of life, before they begin their own DTaP vaccination series. A recent CDC-funded study published in MMWR found that maternal Tdap vaccination was 78% effective at preventing pertussis infection in infants under two months old, the period when infants are at the highest risk and too young to be vaccinated themselves. Even more compelling, Tdap reduced the risk of hospitalization from pertussis by 90%, underscoring its role in protecting against severe disease. Other studies have corroborated these findings: for example, a systematic review found that maternal Tdap was associated with a 69–91% reduction in infant pertussis cases within the first three months of life. Additionally, a 2018 study in Pediatrics reported a 91.4% vaccine effectiveness against pertussis-related hospitalization when mothers were vaccinated during pregnancy. These findings support the public health strategy of prenatal vaccination as the most effective method for shielding newborns from serious pertussis complications such as pneumonia, encephalopathy, and death in the critical early weeks.

How many women choose to receive the vaccine:

The most recent data estimate that 59.6% of women receive Tdap during pregnancy in the United States.

Concerns Around Tdap Vaccination During Pregnancy

While Tdap is widely recommended by the major medical associations during pregnancy—primarily to protect newborns from pertussis—many parents and practitioners have raised valid and increasingly common concerns that deserve thoughtful exploration.

One of the most frequently cited issues is the presence of aluminum in the Tdap vaccine.

Aluminum acts as an adjuvant, boosting the immune response to the vaccine. However, aluminum is a known neurotoxin at high levels and has never been proven safe when injected during pregnancy. The Tdap vaccine contains approximately 0.3 to 0.5 mg of aluminum, depending on the brand (Boostrix vs. Adacel), and because it’s injected intramuscularly, it bypasses the gut barrier and is absorbed systemically. Research has shown that aluminum can cross the placenta, and some animal studies suggest it may accumulate in the developing brain or tissues—raising red flags during a time of critical neurological and immune development. Despite this, no long-term human studies have evaluated the fate of vaccine-derived aluminum in utero or the cumulative exposure when combined with other aluminum-containing interventions during pregnancy.

Another concern centers around the potential risk of adverse pregnancy outcomes, including spontaneous abortion, stillbirth, and preterm labor. While several observational studies have not found a statistically significant increase in miscarriage rates following Tdap, critics point out that these studies often rely on retrospective data, lack proper control groups, and do not use inert placebos. This limits our ability to detect more subtle risks or delayed effects. The absence of randomized, double-blind, placebo-controlled trials in pregnant women—a population generally excluded from pre-licensure trials—represents a serious gap in our understanding of Tdap’s true risk-benefit profile in pregnancy. Moreover, long-term developmental outcomes for children exposed to maternal Tdap in utero, such as impacts on neurodevelopment, immune system programming, or allergy risk, have not been thoroughly investigated.

Additionally, stacking multiple vaccines during pregnancy has become a growing concern. Today, it’s common for pregnant individuals to be offered not only Tdap, but also the influenza vaccine, and more recently, the COVID-19 vaccine, often during the same visit. This raises questions about the cumulative effect of multiple immune activations during pregnancy, a time when the maternal immune system is already finely balanced to support fetal tolerance. Some researchers worry that multiple inflammatory signals could increase the risk of pregnancy complications, autoimmunity, or subtle alterations in fetal immune imprinting—especially in women with genetic mutations, autoimmune conditions, or other genetic susceptibilities.

Other concerns include the lack of transparency around safety data, the potential for underreported adverse events in passive surveillance systems like VAERS, and the perception that parents are often pressured into accepting the vaccine without a full discussion of alternatives or the opportunity for truly informed consent.

For example, few providers discuss the option of cocooning (vaccinating close contacts instead of the mother) or emphasize breastfeeding and nutritional support as complementary strategies for immune protection. This has led many thoughtful parents—not necessarily “anti-vaccine,” but concerned and cautious—to question the necessity, timing, and safety of Tdap during pregnancy, especially in the absence of outbreaks or other high-risk factors.

These concerns reflect not a rejection of medicine, but a desire for more individualized, transparent, and evidence-based care that acknowledges the limitations of current research and the unique needs of each pregnancy.

Finally, some opt out of the vaccine not due to data alone, but because of the erosion of medical trust. A growing number of families feel that their individual risk profiles are not considered, and that one-size-fits-all recommendations fail to account for biological variability, environmental exposures, and evolving science. These concerns don’t necessarily come from a place of “anti-vaccine” ideology but from a desire for transparency, better data, and truly informed consent.

For these reasons, while Tdap during pregnancy may offer clear benefits for some families, others choose to decline or delay based on personal health history, philosophical beliefs, or unanswered scientific questions.

So What Should You Do?

In Between a Shot and a Hard Place, I talk a lot about the space between certainty and uncertainty—how well-meaning, thoughtful parents can look at the same data and arrive at different conclusions. And that’s okay. That’s exactly what informed consent is supposed to look like: a conversation, not a command; a process, not a prescription. When it comes to Tdap in pregnancy, the CDC currently recommends the vaccine for all pregnancies, ideally between 27 and 36 weeks gestation. But in practice, roughly half of parents choose to follow that guidance, and half do not. These decisions are often shaped by personal health history, values, risk perception, and trust in the system—not by “misinformation”. The goal of this Substack isn’t to tell you what to do, but to give you a fuller view of the science, the gaps, and the questions still worth asking—so that you can make the decision that’s best for you, your baby, and your family.

PS: Grab a copy of Between a Shot and a Hard Place and join the conversation. Over 4000 parents have purchased the book already!