Temporal and regional differences in the incidence of hospital‐diagnosed endometriosis: a Danish population‐based study

INTRODUCTION: Due to diagnostic challenges, normalization of symptoms and an overall lack of awareness among both patients and physicians, endometriosis is an underdiagnosed disease. This can result in delayed treatment and potentially worsening of the disease. Despite initiatives, such as patients' support organizations and specialized endometriosis referral centers, differences in awareness, socioeconomic factors and lifestyle, combined with varying distances to specialized referral centers, could result in regional differences in the degree of underdiagnosing. This study aims to explore temporal and regional variations in the incidence of endometriosis based on the Danish hospital discharge register, and shed light on the degree of underdiagnosing of endometriosis in Denmark. MATERIAL AND METHODS: This registry‐based cohort study included all women aged 15–55 living in Denmark from 1990–2017. Participants were identified through the Danish Civil Registration system and endometriosis diagnoses received at a hospital were obtained from the Danish National Patient Registry. Incidence rates of diagnosed endometriosis were calculated for each year of the study period and for each municipality in Denmark. A Cox regression analysis, stratified by calendar time and adjusted for ethnic origin, household composition, highest educational level and family socioeconomic status, was performed to estimate the association between residence and likelihood of receiving a hospital‐based diagnosis of endometriosis. RESULTS: The nationwide incidence rate of hospital‐diagnosed endometriosis was 7.89 (95% confidence interval [CI] 7.80–7.99) per 10 000 person‐years and the prevalence in 2017 was 1.63%. The results showed an overall increase in the incidence of diagnosed endometriosis of 46.8% (95% CI 32.9–62.2) during the study period and also displayed significant regional differences. After adjustments, women living in northern Jutland had the highest probability of receiving a hospital‐based diagnosis of endometriosis (hazard ratio 1.13, 95% CI 1.09–1.18), whereas women living in northern Zealand had the lowest probability (hazard ratio 0.63, 95% CI 0.60–0.67) compared with eastern Jutland. These regional differences have become more evident over time. CONCLUSIONS: Our results reveal significant regional differences in the incidence of hospital‐diagnosed endometriosis, suggesting that a significant number of women may be left behind without a diagnosis. Further studies are needed to assess the underlying reasons for the significant regional differences.