WHITE PLAINS, N.Y, Nov. 1, 2013 /PRNewswire/ -- The United States' preterm birth rate dropped for the sixth consecutive year in 2012 to 11.5 percent, a 15-year low. (Photo: http://photos.prnewswire.com/prnh/20130214/DC59689LOGO) Six states – Alaska, California, Maine, New Hampshire, Oregon and Vermont – earned an "A" on the March of Dimes 2013 Premature Birth Report Card as their preterm birth rates met the March of Dimes 9.6 percent goal. The US preterm birth rate improved to the lowest rate in 15 years, but the change wasn't enough to earn it a better grade. The nation again earned a "C" on the Report Card. Please visit the March of Dimes multimedia news release to see videos, pictures or for more information on preterm birth. The March of Dimes estimated that, since 2006, about 176,000 fewer babies have been born too soon because of improvement in the preterm birth rate, potentially saving about $9 billion in health and societal costs. "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. The national preterm birth rate peaked in 2006 at 12.8 percent after rising steadily for more than two decades, according to the National Center for Health Statistics. The 2012 rate is a 10 percent improvement since the 2006 peak and the best rate since 1998. When compared to 2006, almost all states had lower preterm birth rates in 2012.