The rate of preterm births (less than 37 weeks gestation) dropped to 12.7 percent in 2007 from 12.8 percent in 2006, a small but statistically significant decrease. the March of Dimes hopes the finding will prove to be the start of a new trend in improved maternal and infant health. The preterm birth rate declined for babies born at 34-36 weeks gestation (late preterm) and among babies born to African American and white women.