Unique characteristics that distinguish one city from another -- such as region, size and local economy -- may impact preterm birth rates among U.S. women, according to a study in the September-October 2008 issue of Public Health Reports.
These city characteristics may also help to explain some of the long-observed, but poorly understood racial disparities that contribute to a higher preterm birth rate among black women in the U.S., says lead study author Michael Kramer, MS, MMSc, an epidemiology researcher at the Rollins School of Public Health, Emory University.
Kramer and team examined the impact of city size, region of the country, and differences in the economic and educational characteristics of 168 U.S. metropolitan cities on the very preterm (VPT) birth rate among white, black and Hispanic women. Very preterm birth is a birth that occurs before 32 weeks gestation. A full-term birth occurs at or after 37 weeks.
The study found that the city-to-city variation of very preterm births was higher among black women than white women. In each of the cities, black women experienced 2-3 times greater risk for very preterm birth than white women, Kramer says. The difference between highest- and lowest-risk cities for blacks was three times the difference between highest- and lowest-risk cities for whites.
"While it is well reported that there is an overall racial disparity in very preterm birth, this study is one of the first to look at the impact that cities may have on preterm births," says Kramer. "The size of the racial gap between black women and white women changed from one city to another, and suggests that there may be something about the actual places where these women live that could be intervened upon to lower women's risk for preterm birth."
The seven Georgia metropolitan areas included in the analysis mirrored the overall analysis with black women at higher risk for very preterm birth. The risk for VPT birth for white women varied from a low of 0.8 percent in Athens, Ga. to the highest at 1.4 percent in Macon, Ga., while the risk for black women varied from a low of 2.7 percent in Atlanta to the highest at 4.3 percent in Athens, Ga.
Very preterm birth is the leading cause of U.S. infant mortality and one of the strongest risk factors for pediatric disabilities such as cerebral palsy. Decades of research have identified a handful of preterm birth risk factors, but none of which explains the increased risk experienced by U.S.-born black women.
"We already know that public health efforts to reduce racial disparities in pregnancy outcomes must target individual needs," says Kramer. "Now we must also consider characteristics of the places women live if we are to eliminate racial disparities associated with preterm birth."
In addition to Kramer, study authors included Carol Hogue, PhD, MPH, Jules and Deen Terry Professor of Maternal and Child Health, Department of Epidemiology, Rollins School of Public Health, Emory University, and director of the Women's and Children's Center, Rollins School of Public Health, Emory University.
The study was funded by the Health Resources and Service Administration (HRSA), a branch of the U.S. Department of Health and Human Services (HHS).
Reference: Public Health Reports, September-October 2008, Volume 123