Oral contraceptives and endometriosis: the past use of oral contraceptives for treating severe primary dysmenorrhea is associated with endometriosis, especially deep infiltrating endometriosis

BACKGROUND: The relationship between the use of oral contraception (OC) and endometriosis remains controversial. We therefore compared various characteristics of OC use and the surgical diagnosis of endometriosis histologically graded as superficial peritoneal endometriosis (SUP), ovarian endometrioma (OMA) or deep infiltrating endometriosis (DIE). METHODS: This cross-sectional study included 566 patients without visible endometriosis at surgery as controls, and 410 patients with histologically proven endometriosis, categorized by their worst lesions as SUP n = 47, OMA n = 120 and DIE n = 243. Personal data, including on OC use, were prospectively collected during standardized interviews. Statistical analysis was performed using unconditional logistic regression. RESULTS: Past OC users had an increased incidence of endometriosis (adjusted odd ratios (OR) = 2.79, 95% confidence interval (CI) 1.74-5.12, P = 0.002) of any revised American Fertility Society stage. Women who had previously used OC for severe primary dysmenorrhea were even more frequently diagnosed with endometriosis (adjusted OR = 5.6, 95% CI 3.2-9.8), especially for DIE (adjusted OR = 16.2, 95% CI 7.8-35.3). Women who had previously used OC for other reasons also had an increased risk of endometriosis, but to a lesser extent (adjusted OR = 2.6, 95% CI 1.8-4.1). The age at which OC was initiated, duration of OC use and free interval from last OC use were not significantly different between control and endometriosis women, irrespective of histological grading. Current OC users did not show an increased prevalence of endometriosis (OR = 1.22, 95% CI 0.6-2.52). CONCLUSIONS: Our data indicate that a history of OC use for severe primary dysmenorrhea is associated with surgical diagnosis of endometriosis, especially DIE, later in life. However, this does not necessarily mean that use of OC increases the risk of developing endometriosis. Past use of OC for primary dysmenorrhea may serve as a marker for women with endometriosis and DIE.