Howse said at least four factors have had an impact on the premature birth rate. One is that a new treatment to help prevent preterm birth -- progesterone injections -- was approved by the U.S. Food and Drug Administration to treat women who've already had a preterm birth. Another important reason for the decline is that fewer women smoke during pregnancy. The rate of smoking went from 19.6 percent to 17.6 percent of women of childbearing age, according to the report card.
The third factor is that fewer elective labor inductions and cesarean-sections are performed before 39 weeks' gestation, and the fourth reason is a slight improvement in the percentage of women getting into prenatal care early, according to Howse.
"I think where we're really seeing a reduction is in the late preterm births. There's been more and more evidence on not doing elective deliveries before 39 weeks," said Dr. Deborah Campbell, director, division of neonatology at Montefiore Medical Center in New York City.
Howse said what's not as clear-cut is how to make inroads for the half of all preterm births that don't have known causes. "We have to study the problem and develop interventions," she said.
The report card also showed some significant geographic differences in the rates of preterm birth, with higher rates occurring in the Southern states. Howse said that certain risk factors may be present in the Southern states, such as obesity and smoking.
Overall, however, "We are on the road to success," she said. "This trend has held for three years in a row, and epidemiologists would be willing to call that a trend." But a half-million infants are still being born too soon in the United States, she said.
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