Maternal, prenatal and perinatal characteristics and first trimester maternal serum hormone concentrations

In uncomplicated pregnancies, first trimester androgen, oestrogen and prolactin concentrations were higher in nulliparous (n = 160) than parous (n = 260) mothers. Androgens and estrogens were higher in younger than older mothers. These data are consistent with elevated hormone concentrations mediating the breast cancer protection from a first pregnancy and pregnancies occurring at younger ages.