Age at first pregnancy in relation to age at menarche and year of birth in Caucasian, Japanese, Chinese and part-Hawaiian women living in Hawaii.

A multiple regression analysis was undertaken to examine the relationship between age at first pregnancy and recollected age at menarche and sociological variables in Caucasian, Japanese, Chinese and part-Hawaiian parous women living in Hawaii. The analysis was conducted using the medical history records of 1198 Caucasian, 1770 Japanese, 453 Chinese and 578 part-Hawaiian women. Age at first pregnancy varied significantly among ethnic groups. Initial results showed an apparent heterogeneity among ethnic groups in the effect of age at menarche on age at first pregnancy. Once appropriate controls for the linear and non-linear effects of year of birth were made, the effects of age at menarche on age at first pregnancy no longer varied significantly among ethnic groups. The observed secular trends in age at first pregnancy have varied widely among the four ethnic groups studied and appear unrelated to genetic background.