Babies born prematurely in the United States carry a burden of health and environmental problems that cost at least $26.2 billion in 2005 — about $51,600 per infant. And in an era when many conditions that could lead to long-term disability or death are decreasing, preterm births are on the rise.

Premature births in the United States have increased 30 percent since 1981, now representing 12.5 percent of all births, according to a new report from the Institute of Medicine of the National Academies. Utahns provided much of the data used in the report.

"Preterm birth remains the single greatest cause of having a disappointing outcome for pregnancy. It's the leading cause of death, acute and chronic health-care problems for the baby," said Dr. Jay Iams, professor and vice chairman of obstetrics and gynecology at Ohio State University College of Medicine, during a conference call on the report's release Thursday.

The report considers "preterm" any birth before 37 weeks of pregnancy.

The report calls for more research aimed at helping care providers predict and thus prevent preterm births, and boosting understanding of the medical and developmental problems that can afflict preemies.

"This emphasizes the importance of preterm birth as a public health problem in the United States," said Dr. Richard E. Behrman, chairman of the committee that authored the report. "One with significant consequences." Unfortunately, he said, it's growing rather than shrinking. And there are disparities that hit ethnic women particularly hard, although researchers don't know why.

The earlier a baby is born in its development, the graver the potential for disability and illness, but even babies born just a couple of weeks preterm may have trouble with breathing, eating and have higher jaundice rates, said panelist Marie McCormick, professor of society, human development and health at the Harvard School of Public Health. A full-term baby arrives at 38 weeks to 42 weeks gestation. Many of the babies studied for the report were "moderately preterm," meaning they were born around 36 or 37 weeks.

A Caucasian who is healthy and pregnant for the first time has a 10 percent risk of delivering a preterm baby. The risk jumps to 15 percent for African-Ameri- cans, although the vast majority of preterm babies are white. And risk doubles the chance that a woman who was herself born premature will have a preterm baby.

"We have had little success in understanding and preventing preterm birth," said Behrman.