**Why We Know So Little About What Medications Are Safe for Pregnancy**
Despite the widespread use of medications by pregnant people, there remains a significant lack of scientific data on the safety and efficacy of most drugs during pregnancy. This knowledge gap arises largely because pregnant individuals are routinely excluded from clinical drug trials, a practice rooted in historical tragedies and protective regulations but one that experts now argue is doing more harm than good. Addressing this issue is critical to ensuring that pregnant people receive safe and effective medical care without unnecessary fear or risk.
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**The Problem: Exclusion of Pregnant People from Drug Trials**
Less than 1 percent of clinical drug trials conducted from 2008 to 2023 have included pregnant people, even though over 90 percent of pregnant individuals in the U.S. report taking at least one medication during pregnancy. This disparity means that while medications are widely used during pregnancy, there is often little rigorous evidence to guide their safe use.
This exclusion stems partly from a desire to protect fetuses from potential harm. The legacy of thalidomide in the late 1950s and early 1960s—a drug prescribed for morning sickness that tragically caused birth defects in thousands of children worldwide—led to stringent regulations. In 1962, the U.S. Congress amended the Food, Drug and Cosmetic Act to require well-controlled clinical trials for drug approval. Subsequently, pregnant women were classified as a “vulnerable” population, presumed unable to provide informed consent, and thus were routinely excluded from trials.
However, experts now argue this approach is shortsighted. “It’s a little bit shortsighted to say that not including pregnant women in clinical trials actually protects them,” says Alyssa Bilinski, assistant professor of health policy at Brown University. In practice, drugs approved in the general population are often prescribed to pregnant people without any pregnancy-specific safety data. This leaves clinicians and patients making decisions in the dark, balancing potential risks of medication against the harms of untreated illnesses.
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**The Consequences: Fear and Untreated Conditions**
Because of limited data, many pregnant people avoid medications—even those that could alleviate pain or manage serious health conditions—out of fear of harming their fetus. This avoidance can be dangerous. Untreated conditions such as hypertension, diabetes, infections, or mental health disorders can pose greater risks to both the pregnant person and the fetus than the medications themselves.
Sindhu Srinivas, a professor of obstetrics and gynecology at the University of Pennsylvania, emphasizes the need to weigh both sides: “The decision to take a drug while pregnant has to be a balance of, what’s the harm not just of the potential medication, if there is one, but what’s the harm or the benefit of not taking the medication or not taking the vaccine.” Without solid evidence, pregnant people and clinicians must rely on incomplete or anecdotal information, which can lead to suboptimal care.
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**Rethinking Protection: From Exclusion to Inclusion**
There is growing consensus among researchers and health professionals that excluding pregnant people from research does not protect them but rather leaves them vulnerable to unknown risks. Instead, pregnant people should be included in clinical research to ensure that medications prescribed during pregnancy are based on solid evidence.
Shahin Lockman, an immunologist at Harvard T.H. Chan School of Public Health, highlights the importance of considering the mother’s health alongside fetal health. “We have to think about the mother’s health too, not just see them as a vessel for a baby,” she says.
Recent research modeling the impact of including pregnant individuals in drug trials has shown substantial benefits. For example, a clinical trial of thalidomide involving 200 pregnant people could have prevented nearly 8,000 birth defects. Similarly, including pregnant people in COVID-19 vaccine trials would have reduced COVID-related maternal deaths and stillbirths by 20 percent during 2021.
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**Efforts to Fill the Knowledge Gap**
Recognizing the problem, the U.S. government and scientific bodies have taken steps to encourage research involving pregnant and lactating people. The 21st Century Cures Act established the Task Force on Research Specific to Pregnant Women and Lactating Women (PRGLAC), which recommended removing the “vulnerable” designation for pregnant people and issued guidance to the drug industry.
The National Academies of Sciences, Engineering, and Medicine also convened a panel that concluded including pregnant people in clinical trials does not pose significant legal risks to drug companies. While