The U.S. preterm birth rate dropped for the fifth consecutive year in 2011 to 11.7 percent, the lowest in a decade, according to a new report released Tuesday.

Four states -- Vermont, Oregon, New Hampshire, and Maine earned an "A" on the March of Dimes 2012 Premature Birth Report Card as their preterm birth rates met the 9.6 percent goal. The March of Dimes is the leading nonprofit organization for pregnancy and baby health in the U.S.

"These results demonstrate that many premature births can be prevented with the right policies and bold leadership," said Jennifer Howse, president of March of Dimes. "We must implement proven interventions and accelerate our investment in new research to prevent preterm birth so one day every baby will get a healthy start in life."

The U.S. preterm birth rate peaked in 2006 at 12.8, after rising steadily for more than two decades, according to the National Center for Health Statistics. All this improvement means not just healthier babies, but also potential savings of roughly 3 billion U.S. dollars in health care and economic costs to society, said Howse. About 64,000 fewer babies were born preterm in 2010, when compared to 2006, the peak year.

Howse attributed the improved rates to an expansion of successful programs and interventions, including actions by state health officials in 48 states, the District of Columbia and Puerto Rico, who formally set goals to lower their preterm birth rates eight percent by 2014 from their 2009 rate.