Built-in risk for teenage pregnancies.

Physicians have long known that pregnant teenagers face an increased risk of delivering a premature baby. Research has chalked that threat up to a host of social and economic problems, including lack of regular prenatal heath care.

The surprising results of a new study now suggest that pregnant teens from stable backgrounds, who usually get regular maternity care, also have a higher risk of delivering a premature or smaller-than-average baby.

"Becoming pregnant as a young teenager can result in an intrinsic increase in the risk of adverse outcomes of pregnancy," conclude the authors of the study, which appears in the April 27 New England Journal of Medicine.

Most previous studies focused on inner-city adolescents with many risk factors for a dangerous pregnancy.

To home in on any biological risk associated with teen births, R. H. Ward of the University of Utah in Salt Lake City and his colleagues decided to analyze the delivery records of Utah teens. Studies show that pregnant women in Utah are largely married, middle-class, and less likely to smoke or use drugs or alcohol during pregnancy.

Married Utah teens age 13 to 17 who had received adequate prenatal care were twice as likely to deliver a premature infant as similar women age 20 to 24. Teenage mothers were also at risk of having a very small baby, the authors found.

Low birthweight and prematurity increase a baby's chances of suffering mental retardation, blindness, and other serious health disorders, says Charlotte Catz of the National Institute of Child Health and Human Development in Bethesda, Md.

"This particular study showed that even in a population where the young teenagers were married, were going to school, and had prenatal care--they still had a risk that was higher than [that of] the older women," Catz says.

Ward and his colleagues speculate that the apparently inherent risk may result because the young mothers are still growing themselves and thus may compete with the fetus for nutrients. However, no one really knows why teens and their babies face such adverse health risks.

"We need more studies," Catz concludes.