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.