Probabilities of intercourse and conception among U.S. teenage women, 1971 and 1976.

One in five U.S. females have had intercourse by age 16, and two-thirds, by age 19. Almost all the experience is premarital. One in 10 U.S. women get pregnant before age 17; one-quarter before they are 19, and eight in 10 of these pregnancies are premarital. More than one-third of those who are sexually active premaritally have a premarital pregnancy before they turn 19, one-quarter by the time they are 17.