Infant mortality rates in America fell by 12 percent between 2005 and 2011, according to a new report from the Centers for Disease Control and Prevention. Some of the most striking improvements were in Southern states, which traditionally have had much higher rates of infant mortality than the rest of the country.

"The states with the steepest declines in infant deaths — Georgia, Louisiana, North Carolina and South Carolina — have long been plagued with some of the nation’s highest infant mortality rates," said Dr. Marian F. MacDorman, a senior statistician at the National Center for Health Statistics and an author of the report, in an interview with The New York Times. "In all four states the rate dropped by more than 20 percent from 2005 to 2010, the latest year for which state data are available."

While this improvement deserves recognition, MacDorman says people should not start celebrating just yet. "The U.S. infant mortality rate is higher than rates in most other developed countries. In fact, by her reckoning, "the relative position of the United States in comparison to countries with the lowest infant mortality rates appears to be worsening."

MacDorman and her research team believe the main cause of the United States’ high infant mortality rate is related to the country's percentage of preterm births compared to other industrialized nations. One in every 8 births in the United States is preterm, according to MacDorman, whereas only 1 in 18 birth is preterm in Ireland and Finland. She adds that if the United States had Sweden's infant mortality rate, 2.4 per 1,000 births, nearly 8,000 infant deaths would be averted each year.

And from looking at the numbers, continued improvement in the South is vital to reducing the U.S.'s nationwide rate. A graphic created by political blogger Juan Cole using U.S. Census data shows that Southern states average infant mortality rates between 8 and 11 per 1,000 live births, while the Coasts and Midwest average between 4-6 deaths per 1,000.