The U.S. premature-birth rate has hit a record high, the latest CDC figures show.

The new figures cover the year 2003. They show that premature babies now make up 12.3 percent of all births — a 30 percent increase since detailed record keeping began in 1981.

Most of the increase comes from white babies. Their preterm rate hit 11.5 percent. But that record high is dwarfed by the preterm rate for black babies: 17.6 percent, a rate that's barely changed since 1981.

Of even more concern is the "very preterm" rate for blacks. Nearly 4 percent of black babies are born at less than 32 weeks of pregnancy — almost two and a half times the rate for white babies.

The new data are "troubling," says Joyce A. Martin, MPH, lead statistician for the CDC's division of vital statistics. Martin is the lead author of the CDC's newly released Births: Final Data for 2003.

"It is of concern nationally that this important indicator of child health continues to deteriorate," Martin tells WebMD.

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Going in the Wrong Direction

March of Dimes president Jennifer L. Howse, PhD, says premature birth often has devastating consequences for babies and their families.

"It will break your heart: 25 percent of those babies have serious lifelong health consequences," Howse tells WebMD. "Learning disabilities, mental retardation, cerebral palsy, blindness or vision impairment — these are infants who have been damaged and will have a lifetime of disability."

Howse notes that the U.S. Public Health Service has set a goal of reducing the premature birth rate to 7.6 percent by 2010. But the figures show we're steadily going in the wrong direction.

What's going on? Nobody is sure.

"We cannot say from our data what is driving the increase," Martin says. "Some studies suggest that changes in the management of labor and delivery may be driving some of the change. That is the rate of [medically] induced preterm births and the rate of cesarean delivery for preterm births."

Howse says C-sections and induced labor aren't the whole story. Another factor is the increase in multiple births.

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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."

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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.

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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 percent 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 percent 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 percent to 8.7 percent. 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 percent of them smoke a half-pack or more per day.

By Daniel J. DeNoon, reviewed by Michael W. Smith, MD

SOURCES: Martin, J.A. National Vital Statistics Reports, Sept. 8, 2005; vol 54: pp 1-116. Joyce A. Martin, MPH, lead statistician, division of vital statistics, CDC. Jennifer L. Howse, PhD, president, March of Dimes.