But last year teens accounted for just 24 percent of unwed births, down from 50 percent in 1970, she commented.

The increases in unmarried births have been among women in their 20s, she said, particularly those 25 to 29.

Many of the women in that age group are living with partners but still count as unmarried mothers if they haven't formally married, Ventura noted.

The 20s are the prime childbearing years, regardless of whether the mother is married or not, she said.

Among teens, more than 80 percent of mothers were unmarried.

There were 1,470,152 babies born to single women in 2004, 35.7 percent of all births in the country, NCHS said. That was up from 1,415,995 a year earlier.

Births to older women continued to increase, Brady Hamilton of NCHS pointed out, reflecting choices these women are making in terms of careers and having families.

The birth rate for women aged 35 to 39 increased 4 percent from 2003 to 2004. It was up 3 percent for women aged 40 to 44 and 9 percent for those 45 to 49.

Other findings of the report included:

*There was a total of 4,115,590 births in the country in 2004, up from 4,089,950 in 2003.

*Births to whites declined by nearly 18,000 while Hispanics were up 32,000, there was an increase of more than 8,000 in births to Asians and a rise of just 72 births among black women.

*The total birth rate was 14.0 per 1,000 women, down from 14.1 in 2003.

*The birth rate for women aged 15 to 19 was 41.2 per 1,000, down from 41.6 in 2003 and a record low. The teen birth rate was 61.8 in 1991 and has been declining since.

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On the Net:

National Center for Health Statistics: http://www.cdc.gov/nchs