For the second year in a row, preterm births in the United States have declined, and may mark a reversal of nearly three decades of increases.
The decline is modest, however, and the overall rate of children born before reaching 37 weeks in the womb -- 12.3 percent -- remains a problem. Still, the change looks like progress.
"We're hopeful that the decline represents the beginning of a downward trend," says Joyce Martin, lead author of a report from the Center for Disease Control and Prevention's National Center for Health Statistics study.
Between 2006 and 2008, preterm births dropped from 12.8 percent to 12.3 precent of all births. The rate is down among Hispanics, blacks and whites, and all age groups except women older than 40.
Preterm infants are more likely tend to suffer developmental and disabling conditions. In later life, as adults, their odds of developing such chronic conditions as diabetes and heart disease are also higher.
The upward trend in preterm babies started in 1981 and increased 13% by 1990, and by more than 20% before cresting in 2006.
Newborns arriving early now account for more than half a million births. Studies have linked past rises to the advanced age of mothers and fathers, and births that weren't possible before recent technological developments. This led to more multiple births.
Some studies say that unwarranted cesareans and induced labor have boosted preterm birth rates.
"We don't know if there was a concerted effort to change that has resulted in a decline," Martin says. "This report shows declines among cesareans but among vaginal births too, for which, there are no interventions."