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Parental age at childbirth and age of menarche in the offspring.

BACKGROUND
Early age of menarche (AOM) is associated with serious health problems including breast cancer and heart disease. Rising parental age at childbirth is associated with some adverse health outcomes in the offspring, but whether early menarche is one of them is not known.


METHODS
We studied a Danish cohort of singleton females (n = 3168) born in 1984-1987. Prenatal data were collected from mothers around 36th week of pregnancy (self-administered questionnaire), although the menarcheal age was collected from daughters aged 17-21 years in 2005 (Web-based questionnaire). We assessed each parental age association in separate linear regression models adjusted for covariates (socioeconomic status, parity, maternal pre-pregnancy BMI, marital status, maternal smoking and daughter's self-reported BMI), then included both ages in a third model.


RESULTS
Each year increase in maternal age showed a 9 day earlier onset of menarche in daughters [95% confidence interval (CI): -15.98, -2.90] and a 5 day earlier onset for each year increase in paternal age [95% CI: -10.85, 0.00], after adjusting for covariates. However, these associations attenuated when adjusted for the other parent [change in AOM in days: (i) maternal: -8.49 (95% CI: -17.09, 0.12), (ii) paternal: -1.14 (95% CI: -8.13, 5.84)].


CONCLUSIONS
We found no significant association between parental age and AOM, but the small sample of advance aged parents (over 30 years) limits the information we have. Future studies with a larger sample or a sample with over-representation of older parents will be of value.