Women and their partners in the United States are increasingly using male condoms when they have premarital sex for the first time, which may explain why teenage birth rates have declined in recent decades, according to a new government survey of contraceptive methods.

The proportion of women who used some form of contraceptive the first time they had premarital sex rose to 84 percent in the survey compared with 55 percent before 1985. Most of the increase came from the growing use of a male condom, used by 72 percent of women at first intercourse compared with 34 percent before 1985.

Contraceptive use varied greatly by the education level of parents. About 84 percent of women whose mother had a college education used contraception the first time they had sex compared with 53 percent of women whose mothers did not finish high school.

The numbers come from the National Survey of Family Growth , which is conducted every six to seven years by the Centers for Disease Control and Prevention. The most recent survey was carried out from 2006 to 2008, and its results were released for the first time Wednesday.