Black women are nearly four times more likely than white women to have a baby born between 16 and 22 weeks gestation, a time period in which the life of a baby outside the womb is not viable.

The racial disparity in what are known as "previable" preterm births may explain much of the racial disparity in infant mortality, according to a new study published online in the American Journal of Obstetrics and Gynecology.

"This is promising information since there is emerging evidence to support the effectiveness of screening and treatments to reduce the rate of spontaneous preterm birth, such as cervical length screening and the use of progesterone," says Emily DeFranco, DO, a physician-researcher at the Center for Prevention of Preterm Birth at Cincinnati Children's Hospital Medical Center and a professor of maternal-fetal medicine at the University of Cincinnati.

"Our findings suggest that public health efforts should focus on access to prenatal care, optimizing opportunities for preterm birth screening and preventive efforts in high-risk black women to close the racial disparity gap in infant mortality."

Dr. DeFranco and her colleagues studied all live births in Ohio between 2006 and 2012, totaling more than 1 million. Only one-fourth of 1 percent of live births occurred at 16-22 weeks. The rate of previable birth in black mothers was 6.9 per 1,000, while the rate in white mothers was 1.8 per 1,000 live births.

Preterm birth screening and preventive efforts in the United States have been associated with a declining preterm birth rate in recent years, according to Dr. DeFranco, but the racial disparity in previable births has not declined. She emphasizes the importance of pre-conceptual steps to close the disparity, including optimizing maternal health prior to pregnancy, secure housing and food, access to transportation, avoiding unplanned pregnancies and planning a 12-24 month interval between pregnancies.

Other factors found to be strongly associated with previable birth included having multiples, genetic abnormalities, congenital anomalies, and prior preterm birth.