Background-Influences of female hormones on the occurrence of allergic disorders have been suggested. Age at menarche may be a marker of endogenous oestrogen levels. Data from a Finnish birth cohort followed to adulthood were analysed to determine whether there is any association between maternal age at menarche and the occurrence of atopy among oVspring. Methods-The study was conducted in 5188 subjects born in northern Finland for whom data collections were started during pregnancy and a follow up examination was completed at the age of 31 years. Atopy was determined by skin prick tests with cat, birch, grass, and mite extracts, and doctor diagnosed asthma was ascertained by questionnaire at follow up. Maternal age at menarche was obtained from perinatal data. Logistic regression models were used to adjust for maternal age, parity, smoking, season of birth, parental allergy, and measures of adiposity and socioeconomic status. Results-The prevalence of atopy at the age of 31 years was lower in children whose mothers reached menarche at a later age, especially after age 15. Compared with children whose mothers started menarche at the age of 16 or over, the adjusted odds ratios of being atopic for children whose mothers started menarche younger than or at 12, 13, 14 and 15 years were 1.43 (95% CI 1.12 to 1.83), 1.29 (95% CI 1.03 to 1.60), 1.15 (95% CI 0.93 to 1.42), and 1.19 (95% CI 0.95 to 1.48), respectively. Among girls, the oVspring's own age at menarche was not significantly associated with atopy. Conclusion-Our results encourage further evaluation of the potential eVect of maternal age at menarche on the later development of atopy and possible biological mechanisms.

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