ATLANTA — Out-of-wedlock births in the United States have climbed to an all-time high, accounting for nearly four in 10 babies born last year, government health officials said Tuesday.

While out-of-wedlock births have long been associated with teen mothers, the birth rate among girls ages 10 to 17 actually dropped last year to the lowest level on record. Instead, births among unwed mothers rose most dramatically among women in their 20s.

Experts said the overall rise reflects the burgeoning number of people who are putting off marriage or living together without getting married.

They said it also reflects the fact that having a child out of wedlock is more acceptable nowadays and not necessarily the source of shame it once was.

The increase was seen in all racial groups.