Fewer than 1% of U.S. clinical drug trials enroll pregnant participants, study finds

PROVIDENCE, R.I. [Brown University] - A new studyby researchers from the Brown University School of Public Health found that pregnant women are regularly excluded from clinical drug trials that test for safety, raising concerns for the efficacy of these medications for maternal and child health.

The study, published in the American Journal of Obstetrics and Gynecology, analyzed 90,860 drug trials involving women ages 18 to 45 from the past 15 years and found that only 0.8% included pregnant participants. About 75% of the studies excluded them, potentially leaving critical safety and efficacy questions unanswered.

"When pregnant women are excluded from drug trials, it is harder to know if the medication is safe for mothers and their children," said Alyssa Bilinski, an assistant professor of health services, policy and practice and of biostatistics at Brown's School of Public Health. "In practice, this means that some people might decide to take medications even absent rigorous evidence, which could lead to harmful side effects. At the same time, others might avoid medications that could actually help them because there's not enough data to give them confidence about safety."

About 24% of the studies the researchers looked at did not specify in the data whether pregnant participants were included, but further investigation suggested that they were generally excluded from such trials. Trials that included participants who were pregnant focused primarily on pregnancy-related conditions, labor and prevention of preterm labor. Chronic conditions affecting pregnant women and their children such as diabetes and asthma were largely overlooked.

"We found only 19 trials for non-infectious chronic conditions like anxiety, depression and asthma that have included pregnant participants," Bilinski said. "While it may seem risky to include pregnant people in research, it's even worse to leave them guessing based on incomplete information."

Importantly, rates of inclusion of pregnant participants in drug trials have not changed in 15 years, despite calls for greater involvement, the researchers showed in their findings.

Randomized control trials follow a standard process for evaluating the safety and efficacy of medications. They work by administering treatment to a randomly selected group of participants while withholding treatment from others. These trials have proven to reliably demonstrate a drug's efficacy and potential side effects.

Bilinski noted that it wasn't until 1962 that the U.S. Food and Drug Administration mandated that pharmaceutical companies demonstrate the safety and efficacy of their medications, and only in 1993 were trials required to include women.

"That really wasn't that long ago," Bilinski said. "Our hope is that 30 years from now, lacking high-quality evidence about medication safety during pregnancy will seem as strange and outdated as excluding women from trials seems to us today."

Along with Bilinski, Natalia Emanuel, a research economist at the Federal Reserve Bank of New York, contributed to the work using data from ClinicalTrials.gov.