Age of menarche and time to pregnancy.

STUDY QUESTION Is age of menarche (AOM) associated with subfecundity and/or infertility in adulthood? STUDY ANSWER A late onset of menarche was associated with a slightly increased risk of subfecundity and infertility. WHAT IS KNOWN ALREADY Abnormal age at onset of menarche is a risk factor for several diseases later in life, but the effect on infertility is unknown. STUDY DESIGN, SIZE AND DURATION A cohort study of  73 107 pregnant Danish women enrolled in the Danish National Birth Cohort (DNBC) between 1996 and 2002 with self-reported data on AOM and waiting time to pregnancy (TTP). PARTICIPANTS/MATERIALS, SETTING AND METHODS Information on AOM and TTP was collected through a computer-assisted telephone interview scheduled in pregnancy Week 12. We estimated adjusted odds ratios (ORs) with 95% confidence intervals (CIs) using multivariate logistic regression with TTP categorized as subfecundity (TTP ≥6 months) and infertility (TTP >12 months). Multiple imputation was performed to account for missing data. MAIN RESULTS AND THE ROLE OF CHANCE We found trends towards higher odds of subfecundity and infertility with increasing age of menarche, using 13 years as the starting point. Among women reaching menarche at 15 years, the odds for subfecundity were 1.09 (95% CI: 1.03-1.15), and 1.17 (95% CI: 1.09-1.25) for women reaching menarche later than 15 years compared with the reference group of girls reaching menarche at 13 years. Additionally, women reaching menarche older than 15 years had an OR of infertility of 1.18 (95% CI: 1.08-1.29). Women younger than 11 years at menarche had lower odds of subfecundity. The results were generally attenuated when adjusting for women's age of pregnancy, but the significant positive trend of higher OR for subfecundity persisted, as did the higher OR for subfecundity among women experiencing menarche older than 15 years. LIMITATIONS, REASONS FOR CAUTION We used retrospectively collected self-reported information on AOM and TTP. Information on male factors was limited in this cohort. We only included pregnant women and have therefore no data on women with untreated and unsuccessfully treated infertility, limiting the generalizability to women who became pregnant. WIDER IMPLICATION OF THE FINDINGS This study indicates that the onset of menarche at 15 years or later is associated with subfecundity and infertility. STUDY FUNDING/COMPETING INTERESTS The Danish National Research Foundation has established the Danish Epidemiology Science Centre that initiated and created the DNBC. The cohort is furthermore a result of a major grant from this Foundation. Additional support for the DNBC is obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Augustinus Foundation and the Health Foundation. This specific study was supported by a scholarship from the Ministry of Science and Innovation. No conflict of interest declared.