[men-ar-key or men-ar-key]
a woman’s first menstrual period. Early menarche (before age 12) is a risk factor for breast cancer, possibly because the earlier a woman’s periods begin, the longer the breasts are exposed to estrogen. See also estrogen, risk factor.
... combinations of number of live births (nulliparous, 12, 3þ, unknown), age
at first birth (<25, 2529, 30þ, unknown), age at menarche (<12, 12, 13 ...