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Why We Still Don’t Know Which Drugs Are Safe During Pregnancy

It's not unethical to test drugs on pregnant women. So why aren't we doing it, to help future pregnant women?

Determining what medications are safe for pregnant women is somewhat of a scientific paradox. On one hand, mothers-to-be have historically been excluded from drug research, because subjecting them to scientific studies seemed too risky. On the other hand, experts argue that having millions of pregnant women take essentially untested drugs because we haven’t allowed other pregnant women to enter drug trials is also unethical. Now, doctors, ethicists, and industry leaders are working to solve this problem through a new task force within the  National Institute of Child Health and Human Development.

“It’s absolutely possible to do studies in pregnant women,” Catherine Spong, an obstetrician leading the task force, told STAT News.

True, scientists don’t want to expose vulnerable fetuses to chemicals that could cause birth defects. But in not doing so, they could still be exposing fetuses to chemicals that could cause birth defects. Thalidomide is an excellent example. A medication prescribed to pregnant women throughout the late 1950s to treat nausea, thalidomide was pulled from the market in 1961 only after it had caused approximately 10,000 babies to be born with deformed limbs and brain defects. True, testing thalidomide on a handful of pregnant women could have exposed some infants. But fewer than 10,000, presumably.

Nonetheless, most clinical trials exclude pregnant women as a matter of course. Some err on the side of caution so much that women of childbearing age are required to use two forms of birth control to participate. Up until January 2017, researchers were seldom able to act otherwise, as federal law categorized pregnant women as a “vulnerable population”, similar to those with mental disabilities. In 2018, when the new categorization kicks in, researchers will be allowed to include pregnant women in trials, but still only if they meet strict requirements — including demonstrating that the study is for the benefit of a pregnant woman or fetus. If it doesn’t, then they must prove that the trial poses minimal risk.

The task force will likely push for even more lenient standards. Although they will not present recommendations until next year, experts advocating for change argue that, unless studies in pregnant animals indicate that the drug poses a risk, pregnant women should not be excluded from routine trials. 

In the meantime, scientists can also improve the information available by increasing the number of retrospective studies on pregnant women already taking medication. Likewise, they can analyze datasets of children whose mothers took medication while pregnant with them. “There’s a lot of research that can be done without imposing any risk on [pregnant women] whatsoever,” Anne Lyerly, a physician and bioethicist at the University of North Carolina, Chapel Hill, told STAT. “It’s really no-brainer research.”  

Convincing the public that experimenting on pregnant women is a good thing promises to be a tough sell. But as long as pregnant women need medication, they need drugs that they can rely upon. “Research with pregnant women is the ethical thing to do,” Lyerly says. “Not doing the research is unethical.”