Onset of fertility-related events during adolescence: a prospective comparison of Mexican American and non-Hispanic white females.

Ethnic differences in the first occurrence of fertility-related events are assessed for non-Hispanic White and Mexican American female adolescents. A community-based sample of 1,023 females ages 13 to 19 years was interviewed in 1984-85; 874 (85.4 percent) were reinterviewed approximately two years later. Mexico-born Mexican Americans have the lowest rate of early sexual intercourse, but the highest rate of early births because they are most likely to become pregnant if sexually active, and most likely to have a birth if pregnant. Non-Hispanic Whites have the highest rate of early sexual intercourse, but the lowest rate of early births because pregnant non-Hispanic Whites terminate pregnancies most often. US-born Mexican Americans are intermediate between the other two groups. Delays in the onset of sexual activity among Mexican Americans are not converted into corresponding delays in first pregnancies and births. Early marriage among Mexico-born Mexican Americans, however, accounts for much of the ethnic difference in early fertility.