WASHINGTON -- The nation's infant mortality rate fell by 12 percent from 2005 through 2011, a promising pattern that researchers say may be due in part to a decline in premature births.
The decline came after a period of stalled progress. Although the infant mortality rate dropped significantly over the 20th century, it remained static from 2000 to 2005, according to a report released in April by the Centers for Disease Control and Prevention.
By 2011, however, the rate had dropped to 6.05 deaths of babies less than 1 year old per 1,000 births, down from 6.87 in 2000. Some of the most striking improvements were in Southern states, which still have higher infant mortality rates than most of the country.
The rate of infant deaths declined the most among black mothers -- a drop of 16 percent from 2005 to 2011. Historically, infant mortality rates among black women have been more than twice those among white women.
"We are seeing a slight narrowing in the gap, and that's very encouraging," said Marian F. MacDorman, a senior statistician at the National Center for Health Statistics and an author of the report. "But the gap is still really big."
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, Ms. MacDorman added. 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. The District of Columbia, which has expanded a home-visit program for poor pregnant women and stepped up other efforts to keep mothers and their babies healthy, saw the biggest drop: from 14.05 deaths per 1,000 births in 2005 to 7.86 in 2010.
The states with the highest infant mortality rates are Mississippi and Alabama, according to the report, but even Mississippi saw its rate drop by 15 percent from 2005 to 2010.
Ms. MacDorman said the nation's rate of premature births -- babies born before 37 weeks of gestation -- peaked at 12.8 percent in 2006 and had dropped every year since then. That is a likely factor in the decline of the infant mortality rate, she said. In 2009, the latest year for which CDC data is available, two-thirds of all infant deaths in the United States were among preterm babies.
Another possible factor is a recent emphasis on preventing planned early deliveries. A growing number of hospitals are not allowing mothers to schedule births before 39 weeks without a medical reason. In 2011, the March of Dimes started a public education campaign, Healthy Babies are Worth the Wait, to reduce medically unnecessary deliveries before 39 weeks of gestation. The Department of Health and Human Services began a similar effort, Strong Start, last year.
"It's been going on for a few years now and I think it has had an impact," Ms. MacDorman said of concerted efforts to discourage early deliveries. "It's maybe leading to just a little change in the culture."
Infant mortality dropped in four of the five leading causes of death from 2005 to 2011: congenital malformations, short gestation/low birth weight, sudden infant death syndrome and maternal complications. The death rate from unintentional injuries rose slightly.
The decline in deaths attributed to sudden infant death syndrome was particularly striking -- the rate went down by 20 percent -- but that could have resulted from changes in the way SIDS is diagnosed and reported, Ms. MacDorman said.
While improving, the nation's infant mortality rate is still high compared with the rates in a number of other developed countries. In 2008, the United States ranked 27th in infant mortality among the 30 countries in the Organization for Economic Cooperation and Development, according to the National Center for Health Statistics.
Janice A. Freedman, executive director of the North Carolina Healthy Start Foundation, a nonprofit group focused on reducing infant death and illness, said that it was difficult to pinpoint reasons for the 20 percent drop in her state's infant mortality rate from 2005 to 2010, but that better education about preventing SIDS was probably one factor.
At the same time, Ms. Freedman said she was concerned that state budget constraints would hamper continuing efforts to curb infant deaths.
"We are cutting budgets and so we are concerned that babies don't get lost in the politics," she said. "Numbers can bump up and down, and there are still racial disparities. So there's still a lot of work to be done."
Kevin Ryan, chief of the women's and children's health section of the North Carolina Division of Public Health, said a particularly important goal was to improve the health of women before they become pregnant, focusing on diet, exercise and prevention of chronic diseases like diabetes.
"In years past, the key was access to early, high-quality prenatal care," Dr. Ryan said. "We're looking more and more at addressing the whole life cycle of girls and young women, not just focusing on the period of pregnancy. That's going to be critical to our success in continuing to improve birth outcomes."