Trends in the incidence rate, type and treatment of surgically verified endometriosis - a nationwide cohort study.

INTRODUCTION: To study the trends in incidence rate, type and surgical treatment, and patient characteristics of surgically verified endometriosis during 1987-2012.

MATERIAL AND METHODS: This is a register-based cohort study. We identified women receiving their first diagnosis of endometriosis in surgery from the Finnish Hospital Discharge Register (FHDR). Quality of the FHDR records was assessed bidirectionally. The age-standardized incidence rates of the first surgically verified endometriosis was assessed by calendar year.

RESULTS: The cohort comprises 49 956 women. The quality assessment suggested the FHDR data to be of good quality. The most common diagnosis, ovarian endometriosis (46%), was associated with highest median age 38.5 years (interquartile range 31.0-44.8) and the second most common diagnosis, peritoneal endometriosis (40%), with median age 34.9 years (28.6-41.7). Between 1987 and 2012, a decrease was observed in the median age, from 38.8 (32.3-43.6) to 34.0 (28.9-41.0) years, and in the age-standardized incidence rate from 116 [95% confidence interval (CI) 112-121] to 45 (42-48) per 100 000 women. The proportion of hysterectomy as a first surgical treatment decreased from 38 to 19%, whereas that of laparoscopy increased from 42 to 73% when comparing 1987-1995 with 1996-2012.

CONCLUSIONS: This nationwide cohort of surgically verified endometriosis showed a decrease in the incidence rate and in the patient age at the time of first diagnosis, even though the proportion of laparoscopy has increased. The number of hysterectomies has decreased. These changes are likely to reflect the evolving diagnostics, increasing awareness of endometriosis, and effective use of medical treatment before surgery.