Though much progress has been made on inclusion of non-pregnant women in research, thoughtful discussion about including pregnant women has lagged behind. We outline resulting knowledge gaps and their costs and then highlight four reasons why ethically we are obliged to confront the challenges of including pregnant women in clinical research. These are: the need for effective treatment for women during pregnancy, fetal safety, harm from the reticence to prescribe potentially beneficial medication, and the broader issues of justice and access to benefits of research participation. Going forward requires shifting the burden of justification from inclusion to exclusion and developing an adequate ethical framework that specifies suitable justifications for excluding pregnant women from research.

In the 1990s, prominent reports emerged indicating that women were underrepresented in biomedical research. By now, the findings are well-known: many significant studies on aging and heart disease were performed without adequate representation of women, and the health concerns of women were frequently under-investigated (General Accounting Office 1992; Merton 1996). Also well-known by now is the progress made following the establishment in the United States of the Women's Health Initiative at the National Institutes of Health (NIH) and the passage of the NIH Revitalization Act of 1993, with provisions that each NIH-funded study include representative samples of subpopulations unless their exclusion can be justified on a basis other than cost. More than a decade later, though some disparities have persisted (Chronic Disease Prevention and Control Research Center at Baylor College of Medicine and Intercultural Cancer Council 2008), women now make up the majority of participants in clinical research (General Accounting Office 2001).

This reticence brings with it a profound cost. Of the more than four million women giving birth in the United States every year (Martin et al. 2007), many face medical conditions during their pregnancies that require clinical treatment, but they lack adequate data to inform their care. Indeed, chronic diseases during pregnancy are common: chronic hypertension and diabetes each complicate nearly 4 percent or 40,000 pregnancies each year (Martin et al. 2007); an estimated 500,000 pregnant women experience psychiatric illness (American College of Obstetricians and Gynecologists 2007); cancer, autoimmune disease, and a plethora of other conditions commonly occur with pregnancy and often require treatment. Further, gestation engenders a host of pregnancy-specific conditions that range from difficult (extreme nausea and vomiting) to disabling (sciatic nerve compression) to life-threatening for the woman or her fetus (preeclampsia). Pregnancy is not a prophylaxis against medical illness.