U.S. women in their 30s and early 40s had higher birth rates in 2003, while births among teenagers fell for the 12th straight year, federal health officials said on Tuesday.

The Centers for Disease Control and Prevention (CDC) said the rising birth rates among older women show a continuing trend of delayed childbirth as more women enter the work force.

“These women are actively engaged in education and pursuing their careers” in their 20s, said Brady Hamilton, a statistician with the CDC’s National Center for Health Statistics.

Among women 30 to 34 years old, birth rates rose four percent last year to 95.2 births per 1,000 women from 91.5 births in 2002, the preliminary CDC data showed. The birth rate was up six percent for women aged 35 to 39, and five percent for 40- to 44-year-olds.

The birth rate for women between the ages of 45 and 54 was unchanged, the CDC report found.

Among women aged 20 to 24, birth rates were down one percent, while rates increased two percent for women in their late 20s.

Meanwhile, the birth rate among teens 15 to 19 years old dropped to 41.7 births per 1,000 from 43 births in 2002, suggesting that this age group was practicing abstinence and more responsible sexual behavior, Hamilton said.

Last week, the CDC reported the birth rate among younger females aged 10 to 14 reached a 58-year low in 2002.

The latest report also found that fewer mothers-to-be smoked during pregnancy, while the percentage of women who received early prenatal care increased in 2003, continuing a pattern that began in the early 1990s.

The figures were compiled from birth records in all 50 states, the Atlanta-based CDC said.