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    Rate of Premature Birth Hits New High in U.S.

    CDC Says Preterm Births Now Make Up About 12% of All Births

    Are Fertility Drugs to Blame?

    There's certainly been an increase in the number of women using fertility drugs. These drugs increase the number of multiple births -- and twins, triplets, and other multiple babies are much more likely to be premature than singleton babies. But that's far from the whole answer.

    "The preterm birth rate has been increasing fairly steadily for the last couple of decades for singleton births," Martin says. "Although multiple births have driven the preterm rate up somewhat, it is not responsible for the overall rise."

    Howse notes that obese women are much more likely to have a premature baby than normal-weight women. As America's obesity epidemic continues, premature birth is yet another way the health effects are visited on a new generation.

    Another cause of premature birth, Howse says, is the increasing lack of health insurance by women of childbearing age.

    "One in five women of childbearing age lacks health insurance," she says. "That is a factor, and it is on the rise."

    The X Factor

    But the biggest cause of premature birth is something Howse calls factor X.

    "Factor X is a mother who does everything right in her pregnancy. She has no known risks during her pregnancy. And yet she delivers preterm," Howse says. "Factor X accounts for one half of premature births. We do not know the reasons."

    What's needed, Howse says, is vastly more research. Doctors don't know the full molecular biology of normal pregnancy. That black box may very well hold the key to reducing premature births and the death and disability premature birth leaves in its wake.

    Teen Births Down, More Unmarried Moms

    Not all the news from the CDC report is bad. The teen birth rate continues to drop. It fell by 3% to 41.6 births per 1,000 women aged 15-19. That's one-third of the peak rate seen in 1991.

    The drop in teen births has been particularly dramatic among black teens. Their overall birth rate dropped by nearly half since 1991.

    Other statistics from the new treasure trove of birth data:

    • There was a steep increase in childbearing among unmarried women. After eight years of little change, the birth rate for unmarried women aged 15-44 went up 3% to 44.9 births per 1,000. More than 1.4 unmarried U.S. women gave birth in 2003 -- the most in 60 years.
    • Moms are getting older. The birth rate for women aged 20-24 went down, while the birth rate for women aged 30-34 and 35-40 went up. The birth rate for women 40-44 soared by 5% to 8.7%. That's the highest it's been since 1969.
    • Low birth weight -- babies weighing 5.5 pounds or less -- went up to the highest level since 1970.
    • Cigarette smoking by pregnant women went down. But more than one in 10 pregnant women still smoke -- and about 25% of them smoke a half-pack or more per day.

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