Cohort studies in the context of obstetric and gynecologic research: a methodologic overview.

Observational cohort studies represent one of the most powerful designs in epidemiology. They are also the basis of evidence in many areas of obstetric and gynecologic research, given that randomization of women, couples or pregnancies is often impossible or unethical. Indeed, well-conceived cohort studies have led to a better understanding of many important clinical and public health questions over time, including the impact of different exposures on perinatal and pediatric outcomes in pregnant women and their children. In this paper, we describe the main features, challenges, and limitations of cohort studies in the context of obstetric and gynecologic research. As with all epidemiologic studies, cohort studies present numerous challenges and are vulnerable to bias. However, as we describe throughout this review, careful design - from formulating the study question to planning statistical analysis - can reduce the potential for bias. When possible, we also provide examples from the gynecological and obstetrical literature to illustrate the epidemiological challenge and suggest specific readings.