• Rama Saha, Ralf Kuja-Halkola, Per Tornvall, and Lena Marions.
• 1 Department of Clinical Science and Education Södersjukhuset, Karolinska Institutet .
• J Womens Health (Larchmt). 2017 Feb 1; 26 (2): 152-158.

ObjectivesDespite the high prevalence of endometriosis among women of reproductive age, risk factors or markers for developing the condition remain largely unknown. Many of the published studies are based on small selected samples. We therefore investigated the relationships of reproductive and lifestyle factors with endometriosis in a large sample of Swedish female twins.Material And MethodsThis cross-sectional study included 28,822 women. Among these, endometriosis was reported by 1,228 women and the self-reported diagnosis was confirmed by medical records. Potential risk factors or markers for risk considered were age at menarche, level of education, body mass index (BMI), parity, oral contraceptive (OC) use, infertility, coffee consumption, smoking, and alcohol intake, which were investigated using logistic regression with crude and adjusted analyses. We performed within-pair analysis to examine the sensitivity of the results.ResultsLate age at menarche and higher parity showed an inverse association and infertility showed a strong association with endometriosis. We observed positive associations with coffee consumption and smoking and an inverse association with OC use in crude analysis but not in adjusted analysis. There were no significant associations between level of education, BMI, or alcohol intake and endometriosis. Within-pair analysis showed persistent inverse association of parity and association of infertility with endometriosis.ConclusionsOur study suggests that late age at menarche and higher parity are inversely associated and infertility is strongly associated with endometriosis. Future studies are needed to explore the significance of these factors in the diagnosis of endometriosis and understanding of its etiology.

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