Incidence of endometriosis by study population and diagnostic method: the ENDO study.

OBJECTIVE: To estimate the incidence of endometriosis in an operative cohort of women seeking clinical care and in a matched population cohort to delineate more fully the scope and magnitude of endometriosis in the context of and beyond clinical care.
DESIGN: Matched-exposure cohort design.
SETTING: Surgical centers in the Salt Lake City, Utah, and San Francisco, California, areas. PATIENT(S): The operative cohort comprised 495 women undergoing laparoscopy/laparotomy between 2007 and 2009, and the population cohort comprised 131 women from the surgical centers' catchment areas. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Incidence of endometriosis by diagnostic method in the operative cohort and by pelvic magnetic resonance imaged (MRI) disease in the population cohort. RESULT(S): Endometriosis incidence in the operative cohort ranged by two orders of magnitude by diagnostic method: 0.7% for only histology, 7% for only MRI, and 41% for visualized disease. Endometriosis staging was skewed toward minimal (58%) and mild disease (15%). The incidence of MRI-diagnosed endometriosis was 11% in the population cohort. CONCLUSION(S): Endometriosis incidence is dependent on the diagnostic method and choice of sampling framework. Conservatively, 11% of women have undiagnosed endometriosis at the population level, with implications for the design and interpretation of etiologic research. Published by Elsevier Inc.