Trailing behind other industrialized nations, the US was given a mediocre score of "C" on the March of Dimes 2013 Premature Birth Report Card, despite preterm births being at a 15-year low.

The survey reports that since 2006, when the national preterm birth rate peaked at 12.8 percent, more than 175,000 fewer babies have been born preterm, equaling nearly $9 billion savings in heath care and other social costs, the March of Dimes said.

While almost all states reported lower preterm birth rates when compared to 2006, only a handful were awarded the survey's highest marks. Six states -- Alaska, California, Maine, New Hampshire, Oregon and Vermont -- earned an "A" rating by meeting the March of Dimes' goal of 9.6 percent. Louisiana, Mississippi, Alabama and Puerto Rico received an "F" rating.

"Although we have made great progress in reducing our nation's preterm birth rate from historic highs, the US still has the highest rate of preterm birth of any industrialized country. We must continue to invest in preterm birth prevention because every baby deserves a healthy start in life," said March of Dimes President Dr. Jennifer L. Howse. "A premature birth costs businesses about 12 times as much as uncomplicated healthy birth. As a result, premature birth is a major driver of health insurance costs not only for employers."

Being born prematurely also raised the potential for a host of other medical, behavioral and social issues down the road. For example, a study recently published in the journal PLOS ONE reported that children who were born prematurely went on to score lower on tests when compared to children carried to full term.

Of all racial groups represented in the US survey, non-Hispanic black infants were most frequently born prematurely, at a rate of 16.5 percent in 2012. However, that figure reflects an improvement from 18.5 percent in 2006 and is the lowest recorded in two decades.

"Preterm birth (before 37 weeks of pregnancy,) is a serious health crisis that costs the US more than $26 billion annually," the March of Dimes wrote in a news release. "It is the leading cause of newborn death, and babies who survive an early birth often face the risk of serious and sometimes lifelong health problems, such as breathing problems, jaundice, developmental delays, vision loss and cerebral palsy. Babies born just a few weeks too soon have higher rates of death and disability than full-term babies. Even infants born at 37-38 weeks of pregnancy have an increased risk for health problems compared to infants born at 39 weeks."

The March of Dimes report did not appear to factor in a recent redefinition for full-term pregnancy by the American College of Obstetricians. Previously, a full-term pregnancy was defined as one between 37 and 42 weeks. The new definition of full-term is narrower, only considering babies born in the 39th or 40th week as full-term. "Early-term" now refers to a child born in the 37th or 38th week; "late-term" refers to birth in the 41st week and "post-term" is now used to describe any baby born after week 41.

Click through for more detailed results of the March of Dimes 2013 Premature Birth Report Card.