As teen births drop, experts are asking why.

The birth rate among young adolescents aged 10 to 14 has fallen to the lowest level since 1946, according to a recent report released by the Centers for Disease Control and Prevention (CDC).

"We are encouraged by our continued progress in reducing births to teens of all ages, but we're particularly pleased to make this kind of progress in such a young and vulnerable group," said CDC Director Julie Gerberding.

This report, Births to 10 to 14 Year-Old Mothers, 1990-2002: Trends and Health Outcomes, is the first-ever analysis of births to this group of very young mothers, and was prepared by the CDC's National Center for Health Statistics.

Between 1990 and 2002, almost 137,000 of these young mothers delivered a live birth. This number has declined steadily from a peak of 12,901 in 1994, to the current low of 7,315. If the 1990 rate had held through 2002, there would have been 34,336 additional births to the youngest teens.

The 38 percent decline in the number of births occurred despite the 16 percent rise in the female population aged 10 to 14 years.

About two-fifths of the pregnancies among 10-14 year-olds in 2000 ended in a live birth, two-fifths ended in induced abortion, and about one in six ended in a fetal loss. These proportions have been fairly stable since national pregnancy estimates began in 1976.

In 2002, the birth rate per 1,000 females aged 10-14 years was 0.7 live births, one-half that of 1990 (1.4 per 1,000) and the lowest level since 1946 (0.7).

The 2002 rates were highest among non-Hispanic black (1.9 per 1,000) and Hispanic adolescents (1.4 per 1,000). Though this represents a significant decrease from 1990 rates for non-Hispanic blacks (5.0) and Hispanics (2.4) their rates remained consistently higher than for other groups.

The rates for Asian or Pacific Islander and non-Hispanic white young teens continued to be the lowest, 0.3 and 0.2 per 1,000, respectively. The rate for Asian or Pacific Islander young teens reflected a decrease from their rate of 0.7 per 1,000 in 1990 while the rate for non-Hispanic white young teenagers decreased from 0.5 per 1,000.

Across the U.S., birth rates to the youngest teenagers in 2000-2002 ranged from the national low of 0.2 per thousand in Maine to a high of 2.0 in Mississippi and the District of Columbia.