The objective of this study is to investigate the willingness of pregnant women to participate in a randomized placebo-controlled clinical trial, and to explore the determinants of their decision making. Cross-sectional survey with semistructured interview and thematic content analysis of pregnant women in a tiertiary care obstetric outpatient clinic. Among the 50 women surveyed, 37 (74%; 95% confidence interval, 60-85%) indicated that they would be willing to participate in a randomized placebo-controlled trial of an injectable medicine given throughout pregnancy, while 5/50 (10%; 95% confidence interval, 3-22%) would decline to participate. Potential benefit to the health of the fetus was ranked as the most important determinant for willingness to participate (68%), followed by benefit to personal health (27%), and altruism (5%). A majority of pregnant women would be willing to participate in a randomized placebo-controlled clinical trial. Pregnant women appear to be willing to accept risks to themselves, if there is a chance that participation in a clinical trial would help their pregnancy and improve their baby's health.