title: Reproductive and Lifestyle Factors Associated with Endometriosis in a Large Cross-Sectional Population Sample.
abstract: Despite 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.
  
  
  
  This 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.
  
  
  
  Late 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.
  
  
  
  Our 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.
authors.affiliation: 1 Department of Clinical Science and Education Södersjukhuset, Karolinska Institutet .
authors.forename: Rama
authors.initials: R
authors.lastname: Saha
authors.affiliation: 2 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Ralf
authors.initials: R
authors.lastname: Kuja-Halkola
authors.affiliation: 1 Department of Clinical Science and Education Södersjukhuset, Karolinska Institutet .
authors.forename: Per
authors.initials: P
authors.lastname: Tornvall
authors.affiliation: 1 Department of Clinical Science and Education Södersjukhuset, Karolinska Institutet .
authors.forename: Lena
authors.initials: L
authors.lastname: Marions
mesh_terms: D000328:Adult; D000367:Age Factors; D003430:Cross-Sectional Studies; D004715:Endometriosis / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000453:epidemiology*; D008019:Life Style; D016015:Logistic Models; D008572:Menarche; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012098:Reproduction; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D013548:Sweden
keywords: endometriosis; reproductive lifestyle; twin