Epidemiology of endometriosis in a Norwegian county

Objective. To estimate the prevalence and incidence of endometriosis in Norwegian women aged 40 to 42, and to evaluate reproductive events and life-style as risk factors for endometriosis as well as to evaluate related health-problems. Material and methods. The study was performed partly as a cross-sectional study to estimate occurrence of endometriosis, partly as a case-control study to look for factors associated with endometriosis. The study group consisted of all female inhabitants - born 1950 to 1952 - living in the county of Sor-Trondelag. In connection with a cardiovascular screening program information about reproductive events and gynecological problems including endometriosis and infertility was obtained. Results. Totally 5 139 women were asked to participate, and a questionnaire was completed by 4 034 (78.5%). Endometriosis was reported by 2.0% of the women. Life-time risk for endometriosis was estimated to 2.2%. The annual incidence of new cases of endometriosis in this age group is less than 0.3%. There was a significant association between endometriosis and menarche before age 13, and frequent menstrual periods. Nulliparity was more common in women with endometriosis as were infertility problems and pelvic pain. No significant association was found between endometriosis and exercise, smoking, body mass index and education. There was a high risk for women with endometriosis having had cervical conization or gynecological laparotomies such as infertility surgery, operations on ovaries as well as hysterectomies. Conclusion. In Sor-Trondelag county the prevalence of endometriosis is 2.0% and the annual incidence is less than 0.3% for women in their early forties. A woman's life-time risk for endometriosis might be 2.2%. Early menarche, frequent menstruations, pelvic pain, infertility and nulliparity are associated with endometriosis.