The nation's preterm birth rate fell in 2013, but caregivers cautioned that there are still too many premature babies.
A new report card from the March of Dimes indicates that preterm births in the United States dropped to 11.5 percent in 2012—that's a 15-year low and the sixth year in a row where the rate has fallen. But the same report revealed that premature birth is the leading cause of newborn death in the U.S.
Idaho was given a "B" from the March of Dimes for having a 10.3 percent premature birth rate. That's down from 11.6 percent in 2006, but March of Dimes also said that Idaho was "moving in the wrong direction" by having a 28.1 percent rate of uninsured women and 21.6 percent of women who smoke.
Three states—Louisiana, Mississippi and Alabama—received "F" grades. Six states received an "A" grade: Alaska, California, Maine, New Hampshire, Oregon and Vermont.
About 450,000 babies are born prematurely each year, which is defined as a birth at least three weeks before their expected due date.
At least 80 countries have rates of preterm births below 9.6 percent, according to a United Nations report, "Born Too Soon," released last year. They include China, Romania, Cuba and Latvia. Every developed country has a rate of preterm births lower than that of the United States.