Policymakers, advocates, providers, recipients, and health services researchers all would agree that too little is known about the nature and effects of specific components of prenatal care. In the process of designing a national, longitudinal study of pregnancy and childbirth, we surfaced some methodological dilemmas that help to explain why so little is known. This article explores two of the major problems: (1) selecting a valid scientific sample of pregnant women and (2) collecting data from providers and women. From this analysis, seven methodological questions, which should be investigated through empirical field studies, are identified. Those field studies are essential if future research into the content of prenatal care is to achieve an acceptable level of methodological rigor.