Background: The number of pregnant women with medical comorbidities continues to increase. A large proportion of pregnant women are exposed to medications during pregnancy, but only a fraction of the medications used have been investigated during pregnancy with regard to benefits, risks, and doses.; Methods: This article includes a review of potential deterrents and barriers to pregnant women enrolling in clinical research studies and the federal regulations governing enrollment of pregnant women in research.; Results: Research in pregnant women has been hampered by concerns for liability, the complex physiology of pregnancy with changes related to stage of pregnancy, and federal regulations that deemed pregnant women a vulnerable population. While recent revisions to federal regulations have removed pregnant women from the classification of vulnerable population, regulations regarding consent requirements still limit women's ability to decide on participation in clinical trials. The Department of Health and Human Services established the Task Force on Research Specific to Pregnant Women and Lactating Women to help identify and reduce these barriers.; Conclusion: While recognition of the need for more scientific knowledge on the effects of medications and other interventions in pregnancy is widespread, a number of barriers that hinder enrollment of pregnant women in clinical trials remain.