Six different states, Alaska, California, Maine, New Hampshire, Oregon and Vermont, earned an “A” on the March of Dimes 2013 Premature Birth Report Card because their preterm birth rates met the March of Dimes’ 9.6 percent goal. The preterm birth rate has improved to the lowest rate seen in 15 years, but this change wasn’t enough to earn the U.S. a better grade. The nation once again earned a “C” from the foundation.

The March of Dimes estimates that, since 2006, about 176,000 fewer babies have been born too soon due to improvements in the preterm birth rate. This has potentially saved 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 in a statement. “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.”

According to the National Center for Health Statistics, the national preterm birth rate peaked at 12.8 percent in 2006 after a steady rise for more than two decades. 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 reported lower preterm birth rates in 2012.

The 2012 preterm birth rate among non-Hispanic black infants remains the highest of all the racial groups at an astounding 16.5 percent. However, this was still down from 18.5 percent in 2006 and the lowest reported in more than 20 years.

Preterm birth is a serious health issue that costs more than $26 billion a year in the US, according to the Institute of Medicine. 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.