Surgically confirmed endometriosis in adolescents in Finland—A register‐based cross‐sectional cohort study

INTRODUCTION: Increasing awareness of endometriosis in adolescents requires data on the nature of the disease and its management. Our objective was to investigate the subtypes of surgically confirmed endometriosis in adolescents (aged <20 years) and trends in the incidence rates and endometriosis‐related procedures during the study period, 1987–2012. MATERIAL AND METHODS: In this register‐based cohort study, we identified 526 adolescents receiving their initial surgical diagnosis of endometriosis between 1987 and 2012 from the Finnish Hospital Discharge Register. The age‐specific incidence rate of surgically confirmed endometriosis was calculated by dividing the number of adolescents during specific periods by person‐years. We calculated the relative differences in incidence rates between the periods using crude incidence ratios. RESULTS: Adolescents were divided into three age groups, <17, 17–18, and 19 years, which comprised 8.2% (43/526), 39.7% (209/526), and 52.1% (274/526) of the study cohort, respectively. Peritoneal endometriosis and ovarian endometriosis were the most common types (379/526 [72%] and 119/526 [23%], respectively). The incidence rate of surgically confirmed endometriosis per 100 000 person‐years varied from 5.63 (95% confidence interval [CI] 4.24–7.33) to 11.42 (95% CI 9.64–13.44). The incidence rate in 2001–2005 was significantly higher and was 1.6‐ to 2.0‐fold that of the periods 1987–1990 and 2006–2012, respectively. Comparing the periods in which International Classification of Diseases, Ninth Revision (ICD‐9; 1987–1995) and Tenth Revision (ICD‐10; 1996–2012) codes were used, the use of laparoscopy (78.2% vs 88.9%), day surgery (10.3% vs 31.6%), and procedures for ovarian (18.8% vs 34.1%) and deep (0.6% vs 10.8%) endometriosis increased. The types of endometriosis and procedures did not differ between the age groups. CONCLUSIONS: Peritoneal endometriosis was the most common type of endometriosis overall and by age group. During the 26‐year period, the incidence rate of initial surgical diagnosis of endometriosis peaked in 2001–2005 and decreased thereafter. The proportion of procedures performed for ovarian and deep endometriosis increased, as did the use of laparoscopy and day surgery.