Are Pregnant Women Just "Guinea Pigs" for Vaccine Research?

Why the exclusion from clinical trials doesn't mean what you think it means

A note: We're currently glued to the CDC's ACIP meeting (happening right now!)—listening carefully and will likely share some thoughts and key takeaways in the coming days. Before that, we thought we'd answer a question that came in response to our latest series, Fun Size Science, in which Unbiased Science's resident immunologist, Dr. Aimee Bernard, discusses vaccine safety during pregnancy.

The Question That Sparked This Deep Dive:

This is a question we receive often, and it warrants a detailed response.

We understand concerns about pregnant women being treated as "guinea pigs" in medical research. It's a fair question that touches on some uncomfortable truths. The short answer? No, pregnant women aren't guinea pigs—but the longer answer reveals a complex story about scientific caution, historical injustices, and an evolving understanding of how to protect both pregnant people and their babies.

Pregnant women are historically underrepresented in clinical trials, which means we sometimes have less data about medication and vaccine safety during pregnancy. However, this doesn't mean treatments are unsafe—it means researchers and healthcare providers must carefully weigh available evidence from multiple sources to make informed recommendations. Let's discuss…

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The Historical Context: Why Pregnant Women Were Left Out

The exclusion of pregnant women from clinical trials didn't happen in a vacuum. After the devastating thalidomide tragedy of the 1950s and 1960s, where a seemingly safe sedative caused severe birth defects, the medical community became extremely cautious about testing anything in pregnant women.

This caution was well-intentioned but had lasting consequences. As PATH notes in their comprehensive analysis, the FDA issued policies discouraging the inclusion of women of childbearing age in research—policies that, in practice, led to all women being excluded from many studies until laws mandating inclusion were passed in the 1990s.

The irony? This "protective" approach often left pregnant women with even less information to make informed decisions about their health.

How We Build Evidence for Vaccine Safety in Pregnancy

When people hear that pregnant women are excluded from initial trials, they often assume we're flying blind. But that's not the case. Here's how the science works:

1. Animal Studies Come First

Every vaccine undergoes extensive testing in pregnant animals before any human receives it. These studies screen for potential risks to fetal development. If red flags appear, the vaccine never makes it to human trials.

2. Understanding the Science Behind the Vaccine

Most vaccines recommended during pregnancy—like inactivated flu, Tdap, and COVID-19 vaccines—don't contain live virus. They cannot replicate in the body or cross the placenta in a harmful way. This biological plausibility matters enormously in safety assessments.

3. Real-World Data Collection

Once a vaccine is approved for general use, pregnant women can choose to receive it after discussion with a healthcare professional, even if there is not yet a specific recommendation for use in pregnancy. This decision will be made together after weighing the individual risks and benefits. Those who choose vaccination are carefully monitored through multiple systems:

• V-safe: A smartphone-based monitoring system that has collected data from millions of people, including specific pregnancy registries

• VAERS (Vaccine Adverse Event Reporting System): A national early-warning system that accepts reports from anyone—patients, providers, or manufacturers

• Vaccine Safety Datalink (VSD): A collaboration between the CDC and healthcare organizations that monitors over 9 million people annually using electronic health records

• The COVID-19 Vaccine Pregnancy Registry is a CDC-run program that tracks health outcomes in 23,000 people who received a COVID-19 vaccine during pregnancy to monitor for any potential risks to them or their babies.

What "Off-Label" Really Means

Here's a crucial point that often gets missed: when vaccines are approved for the general population, pregnant women aren't legally or medically barred from receiving them unless there's specific guidance against it.

This is where making collaborative health decisions comes in. Healthcare providers can discuss the available evidence—from animal studies, real-world data, and the biological mechanism of the vaccine—to help patients make informed choices. It's not experimentation; it's evidence-based medicine applied to individual circumstances.

4. Comparative Studies

Researchers conduct observational studies comparing vaccinated and unvaccinated pregnant women, controlling for age, health status, and other factors. Over time, this builds a robust evidence base, often with data from hundreds of thousands of pregnancies.

For COVID-19 vaccines specifically, ACOG notes we now have safety data from "many tens of thousands of reporting individuals" who were vaccinated during pregnancy.

The Changing Landscape: COVID-19 as a Catalyst

The pandemic has accelerated conversations about including pregnant people in research. Some COVID-19 vaccine trials, like this Pfizer study, did include pregnant participants, though this happened after initial vaccine approval.

As PATH observes, "vaccine manufacturers are now adding pregnancy trials to their development strategies at an earlier stage." The question is no longer whether to include pregnant people, but how to do it safely and ethically.

The Ethical Complexity: Protection vs. Autonomy

Here's where things get nuanced. The American College of Obstetricians and Gynecologists (ACOG) has consistently argued that pregnancy should not be treated as a vulnerability that automatically excludes people from research.

In their statements on COVID-19 vaccines, ACOG emphasizes that pregnant individuals are "capable of informed consent" and should be "free to make their own informed decisions regarding COVID-19 vaccination" based on discussions with their healthcare providers.

This represents a shift from paternalistic protection toward respecting autonomy, while still maintaining appropriate safeguards.

The Bottom Line

So, are pregnant women guinea pigs? Absolutely not. The term implies a lack of informed consent and reckless experimentation. In reality:

• Pregnant women choose to be vaccinated based on growing safety evidence

• Decisions are made in partnership with healthcare providers who understand both the benefits and limitations of available data

• The goal is protection of both mother and baby, since infections like flu, pertussis, and COVID-19 can be far more dangerous during pregnancy than the vaccines themselves

• Monitoring systems actively track outcomes to ensure ongoing safety

Looking Forward: Information Equity

The pandemic has highlighted what advocates call "information equity"—the idea that pregnant people deserve robust data to make informed decisions about their health. This doesn't mean rushing into unsafe research, but it does mean being more thoughtful about when and how to include pregnant women in studies. Many scientists now argue that we should celebrate effective vaccines while simultaneously pushing for more inclusive research that studies them in pregnant populations as soon as it's safely feasible.

The changes we're seeing shouldn't end with COVID-19. Moving forward, the goal is to include pregnant women in research as soon as it's safe to do so, avoiding delays that perpetuate information inequity.

The real guinea pigs? They would be the pregnant women left without evidence-based guidance, forced to make decisions in an information vacuum. Today's approach—careful monitoring, collaborative health decisions, and evolving research practices—represents the opposite of that.

Stay Curious,

Unbiased Science

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Current vaccine safety recommendations are based on extensive monitoring and real-world evidence. For the latest guidance, consult with your healthcare provider and refer to ACOG's clinical recommendations.