For the fifth consecutive year, the preterm birthrate in the USAcontinued its slow but steady downward trend, good enough to earn a "C"on a new March of Dimes report card.

The nation's prematurebirthrate is 11.7% of all live births ? the lowest in a decade,according to figures from the National Center for Health Statistics. TheMarch of Dimes has set a goal of 9.6% by 2020.

"We're on theright track," having reversed a trend that included increases every yearfor decades," says Jennifer Howse, president of the non-profitpregnancy and baby health group. Its 9.6% goal reflects the adoption ofmeasures such as getting mothers to stop smoking and providing access toprenatal care.

MORE: Report card on premature births

In2006, the nation's preterm birthrate peaked at 12.8% after risingsteadily for more than two decades. Preterm birth (before 37 weeks ofcompleted pregnancy) is the leading cause of infant death during thefirst month of life.

Having 64,000 fewer preterm babies born from2006 to 2010 resulted in healthier babies as well as a potential savingsof roughly $3 billion in health care and economic costs, the reportsays.

Key signs of improvement in this year's report:

--Four states (Vermont, Oregon, New Hampshire and Maine) earned an "A" formeeting the 9.6% goal; in 2010, only Vermont earned the top grade.

--45 states, the District of Columbia and Puerto Rico posted improvedpreterm birthrates from 2009 to 2011, earning 16 of them better grades.

--The states with the highest preterm birthrates ? Mississippi(16.9%), Louisiana (15.6%), Alabama (14.9%) ? are among 48 states,along with Puerto Rico (17.5%) and the District of Columbia (13.7%) thathave all formally set goals to lower their preterm rates 8% by 2014from their 2009 rates.

Although the preterm birthrate "is not good enough yet," Howse says,"there now is genuine national momentum and leadership to just stay atit until we get the job done."

Key factors that continue to drive the rate of premature births inthe USA include maternal smoking, insufficient access to prenatal healthcare services and late preterm births (infants born between 34 and 36weeks of gestation).

Though late preterm babies are usually healthier than babies bornearlier, they are three times more likely to die in the first year oflife than full-term infants, the March of Dimes says. About 8% ofdeliveries are late-preterm, sometimes the result of medicallyunnecessary elective inductions and Cesarean sections.

"It's very, very important to try to support pregnancies so babiescan be born as close to 39/40 weeks as possible," says pediatricsprofessor Deborah Campbell, director of Neonatology at MontefioreMedical Center in New York.

Just because a baby makes it to 37/38 weeks, "what we call fullterm," doesn't mean that they are fully developed, Campbell says."These babies are more likely to end up in the NICU (Neonatal IntensiveCare Unit), more likely to have acute health issues, and now we'refinding, more likely to have issues as they reach school age."

"Babies need those extra weeks for full development of the brain andlungs," Howse says, adding that unless it is a medical necessity, womenshould wait until at least 39 weeks to schedule an induced labor orC-section.

Worldwide, 15 million babies are born too soon each year and morethan 1 million of those infants die as a result. The USA ranked 131 outof 184 countries in premature births according to a May 2012 report bythe March of Dimes, Save The Children and others.