First birth rates after surgically verified subtypes of endometriosis—a national register study of 9,590 women from Finland

OBJECTIVE: To study first birth rates according to endometriosis subtype after surgical diagnosis among nulliparous women. DESIGN: Retrospective population-based cohort study using Finnish national registers, linking women with first surgical diagnosis of endometriosis to fertility and sociodemographic data. The follow-up started at diagnosis and ended at first birth, sterilization/bilateral oophorectomy/hysterectomy, emigration, death, age of 50 years or December 31, 2019-whichever came first. SUBJECTS: Cohort of 9,590 nulliparous women aged 15-49 years at first surgical diagnosis of endometriosis in 1998-2012 born in 1940-1979. Women were divided into subcohorts: solely peritoneal (n = 3,146, 32.8%), ovarian (n = 3,020, 31.5%), and deep endometriosis (n = 659, 6.9%). Women with combined, rare or unspecified forms of endometriosis comprised the subcohort of combined/other endometriosis (n = 2765, 28.8%). For subanalysis, we included those with prior infertility diagnosis, i.e., presumed pregnancy wish. EXPOSURE: Surgically diagnosed endometriosis. MAIN OUTCOME MEASURES: Incidence rate of first birth. RESULTS: Altogether 5,184 (54.1%) of all women with endometriosis had their first birth after surgical diagnosis of endometriosis. Women with ovarian endometriosis were the oldest at surgical diagnosis (32.5 interquartile range 28.5-37.2 years). The incidence rate of first birth per 100 person-years was 7.67 (95% confidence interval CI: 7.46-7.88) among all women. We calculated the incidence rate ratio between the subcohorts, and the peritoneal subcohort presented significantly higher incidence of first birth (9.44 9.03-9.87) than the other subcohorts. Before surgery, 4,374 (45.6%) women had been diagnosed with infertility, of whom 2,882 (65.9%) had a first birth. Incidence rate of first birth was higher (11.5 11.1-12.0) among these women. The analyses of crude and adjusted restricted mean survival time difference further demonstrated that women with peritoneal endometriosis had a significantly shorter time without first birth compared with women with ovarian or combined/other endometriosis. CONCLUSION: Peritoneal endometriosis was the most favorable subtype in terms of having a first birth. In addition, women with prior diagnosis of infertility had a good prognosis. The overall chance of first birth in women with surgically verified endometriosis seems good, but the findings emphasize the impact of both age and timely diagnosis of endometriosis, in addition to treatment of infertility.