Racial disparities persist in preterm birth risk

NEW YORK (Reuters Health) - Black infants are four times as likely to be born before 28 weeks gestation as white infants, an imbalance that hasn't changed in a decade, a new study shows.

Because such "extremely pre-term" babies are at much greater risk of death than infants born later, this disparity is a major factor in the continuing infant mortality gap between blacks and whites in the United States, Dr. Ashley H. Schempf of Johns Hopkins Bloomberg School of Public Health in Baltimore and colleagues state.

Extremely pre-term infants who do survive are at increased risk of developmental delays and other problems, they point out in the American Journal of Public Health. "There's not a racial disparity that I'm aware of that's as great and as proximally linked to morbidity and mortality as extreme preterm birth," Schempf told Reuters Health.

Disparities in preterm birth, defined as delivery before 37 weeks' gestation, have been reduced in recent years. The researchers sought to determine whether a narrowing of the preterm birth gap between 1990 and 2000 might have resulted in a similar shrinkage of the black-white infant mortality gap.

But during that decade, the researchers found, the racial disparity in infant mortality did not budge. Black babies born in 1990 were 2.3 times more likely to die in infancy than white infants, and black infants born in 2000 were 2.4 times more likely to die before reaching one year of age.

Preterm birth among black infants fell by 10 percent between 1990 and 2000, but increased among white infants by 16 percent, the researchers found.

Meanwhile, there was no change in the racial disparity in extreme preterm birth, Schempf and her colleagues found. Given the high rate of death among these infants, the researchers calculate that this disparity accounted for 60 percent of the overall gap in infant mortality between black and white infants.

Little is known about the causes of preterm birth overall, let alone the reasons for the racial disparities identified by the current study. However, researchers have demonstrated that racial disparities can't be explained by differences in education levels; even among college-educated women, the same if not greater disparities in preterm birth and infant mortality are seen, Schempf said.

"There are likely multiple factors -- social and environmental -- that collide to produce perinatal disparities," Schempf said. "There's ongoing research into things like residential segregation, disparities in environmental quality, and even interpersonal discrimination and stress."

The findings underscore the importance of continuing such research to identify, and address, the factors involved, she added. "Given the sheer magnitude of the disparity and its close link to morbidity and mortality, there are few racial disparities that warrant greater research attention than extremely preterm birth."

SOURCE: American Journal of Public Health, May 2007.