WASHINGTON  Unmarried mothers gave birth to 4 out of every 10 babies born in the United States in 2007, a share that is increasing rapidly both here and abroad, according to government figures released Wednesday.

Before 1970, most unmarried mothers were teenagers. But in recent years the birthrate among unmarried women in their 20s and 30s has soared  rising 34 percent since 2002, for example, in women ages 30 to 34. In 2007, women in their 20s had 60 percent of all babies born out of wedlock, teenagers had 23 percent and women 30 and older had 17 percent.

Much of the increase in unmarried births has occurred among parents who are living together but are not married, cohabitation arrangements that tend to be less stable than marriages, studies show.

The pattern has been particularly pronounced among Hispanic women, climbing 20 percent from 2002 to 2006, the most recent year for which racial breakdowns are available. Eleven percent of unmarried Hispanic women had a baby in 2006, compared with 7 percent of unmarried black women and 3 percent of unmarried white women, according to government data drawn from birth certificates.