Background: The treatment of medical conditions complicating pregnancy is challenged by a serious lack of information about the safety and effectiveness of the medications used by pregnant women. To improve our knowledge of what constitutes the most effective therapy, we conduct systematic research. Research for pregnant women, however, is challenging. The U.S. pharmaceutical industry is the leading conductor of clinical research, yet there is a dearth of published information from industry regarding pregnant women and drug studies. The extent of their exclusion has not been quantified, nor has its rationale been articulated. Industry input will be solicited when FDA releases its new guidance document on pregnant women in clinical research. Methods: To quantify the proportion of pharmaceutical company-sponsored studies that exclude pregnant women, we reviewed exclusion criteria from Phase IV trials posted on ClinicalTrials.gov from October 2011 - January 2012. To articulate the rationa