Genetics Are Key To Age At Which Girls Start Their Periods
 

Genetic makeup explains more than half of the variation between UK women's ages at first period, according to a study of almost 26,000 UK women published today in the May edition of Paediatric and Perinatal Epidemiology. Age at menarche (when periods begin) is known to run in families. However, the balance of genetic and environmental influences on this has been unclear...

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