Incidence, prevalence, and trends in endometriosis diagnosis: a United States population-based study from 2006 to 2015

Background: Accurate estimates of incidence and prevalence of endometriosis among nonselected cohorts are lacking in the United States, and earlier reports have produced varying results.

Objective: This study aimed to define endometriosis incidence and prevalence in a US population and evaluate factors influencing these estimates over time.

Study design: A 10-year retrospective cohort study using Kaiser Permanente Washington electronic health records database was completed. The primary analysis included women enrollees aged 16 to 60 years, from January 2006 to December 2015, who had a uterus, were continuously enrolled for at least 2 years before cohort entry and had at least 1 healthcare utilization. Secondary analysis included all women enrollees aged 16 to 60 years during this time. Incident endometriosis was identified using the International Classification of Diseases, Ninth Revision and Tenth Revision, diagnosis codes. Annual incidence rates were age-adjusted by direct standardization to the 2015 study population. Secular trends in incidence overall and by 5-year age group, race and ethnicity, diagnosis modality, and practitioner type were assessed using Poisson regression analyses. Prevalent cases were defined as women enrolled in 2015 and had an endometriosis diagnosis before the end of 2015. The prevalence rates of chronic pelvic pain and dysmenorrhea defined by the International Classification of Diseases, Ninth Revision and Tenth Revision, diagnosis codes in 2006-2015 were estimated.

Results: Among 332,056 eligible women who contributed 1,176,329 person-years during the 10-year study period, 2863 incident endometriosis cases were identified for an average incidence of 24.3 cases per 10,000 person-years. In our primary analysis, incidence rates declined over the study interval from a high of 30.2 per 10,000 person-years in 2006 to 17.4 per 10,000 person-years in 2015 and were highest among women aged 36 to 45 years in most years. Incidence rates were similar across race and ethnicity groups. The distribution of the 2863 incident cases by the diagnosis modality was as follows: 45.5% surgical, 5.7% imaging, and 48.8% clinical. Endometriosis incidence rates per 10,000 person-years were similar in women who were surgically and clinically diagnosed and decreased significantly from 2006 to 2015 (surgically diagnosed endometriosis dropped from 13.4 to 7.4 and clinically diagnosed endometriosis dropped from 16.1 to 8.9; P value of <.001 for linear trend over time for each). Incident case distribution by diagnosing provider was as follows: 73.6% obstetrician and gynecologist, 15.7% primary care provider, and 10.7% "other." Incidence of endometriosis diagnosed by an obstetrician and gynecologist and primary care provider decreased over the study interval (P<.001 for linear trend over time for each). Method of diagnosis and provider type did not differ by race and ethnicity. Among 135,162 women who contributed person-time in 2015, 2521 women were diagnosed with endometriosis, a prevalence rate of 1.9%. In our secondary analysis, the frequency of chronic pelvic pain diagnosis increased over the study interval from 3.0% in 2006 to 5.6% in 2015.

Conclusion: The incidence rates of endometriosis declined over the 10-year study interval and did so uniformly across age groups, races and ethnicities, and the main diagnosing modalities and providers. Declining rates may reflect a shift in practice patterns in the United States away from the diagnosis of endometriosis both clinically and surgically, rather than favoring more general diagnoses of chronic pelvic pain. The prevalence of endometriosis in 2015 in the United States is in keeping with data from recent studies outside the United States using health record data.