STATE COLLEGE, Pa., May 5 (UPI) -- Studies have shown women are frequently excluded from clinical trials, but a recent study shows it happens at far greater rates than necessary because of concerns related to pregnancy and breastfeeding.
Researchers at Penn State University found in a review of nearly 700 clinical trials for type 2 diabetes that more than half include at least one fertility-related restriction and more than 50 rejected any woman of child-bearing potential, calling into question the results of trials and raising safety concerns about treating some women with the drugs.
In 1993, the National Institutes of Health issued a mandate that women of child-bearing potential should not be routinely excluded from research it funds, but the researchers say the new study suggests they are blocked from participation on unfounded liability concerns.
The researchers say that in addition to previous studies showing women are unnecessarily excluded from trials, other studies show pregnant women are willing to participate if asked to and provided with appropriate information about the trial and risks involved.
"We found that there are widespread limitations on the participation of women of childbearing age in clinical trials," Alannah Phelan, a medical student at Penn State, said in a press release. "There really wasn't a strong association in any direction with drug risk and trial limitations."
For the study, published in the journal Diabetes Care, researchers reviewed 688 phase 2 or 3 clinical trials for type 2 diabetes drugs that were based in the United States and included female participants between ages 18 and 40.
Overall, 59 percent of the studies included one or more fertility-related exclusion, of which 55 percent included one for current pregnancy and 44 percent for breastfeeding.
After ranking drug risk, with lowest risk classified A and highest classified X, the researchers found drugs with higher fetal risk were not necessarily more restrictive. Category C drugs, which showed evidence of fetal risks in animals, were less likely to exclude pregnancy than trials involving category B drugs, and less likely to require contraceptive use to prevent pregnancy during the trial.
More than 50 trials also excluded women of all childbearing potential and 29 required multiple pregnancy tests for women to remain in the trial.
As a result of the restrictions, the researchers are concerned not only about under-representation in studies of a condition that affects a significant number of women, but that excluding women of child-bearing age means nobody knows how the drugs would affect a woman who unexpectedly gets pregnant.
"There are still widespread restrictions placed on participation of women in clinical drug trials, often without justification," Legro said. "Results from these trials may not be generalizable to the larger population. Up to half of pregnancies are unplanned, and we don't know what the effects of these drugs will be on women if they take them and conceive while on them or if they are pregnant."