—Nearly eliminating the practice of inducing labor and C-sections scheduled much ahead of mom's due date unless they're medically necessary. Much of the recent U.S. improvement comes from reducing elective early deliveries, leading to a drop in "late preemies," babies born a few weeks early.
—Helping women to quit smoking. Smoking at some point during pregnancy varies widely, from 10 percent in Canada to 23 percent in the U.S. and 30 percent in Spain, the report found.
—Providing regular injections of the hormone progesterone to certain women at high risk, largely because of a prior preterm birth. A recent NIH survey of obstetricians found just 21 percent of eligible patients received the shots.
—Putting a stitch into the cervix of certain high-risk women, those who have what's called a short cervix.
—Using just one embryo, not multiples, when in vitro fertilization is used.
The impact would vary. The U.S. could see an 8 percent drop in its preterm birth rate by 2015 if it fully implemented these steps, the report estimated, while countries such as Sweden that already have far fewer preemies would see their rates inch down only slightly more, by about 2 percent.
Having one preemie greatly increases the risk for another. Other risk factors include pregnancy before age 17 or over 40, and the mother's own health conditions, such as being underweight or overweight, or having diabetes or high blood pressure. That's why it's so important for women to have good care, not only early in pregnancy, but before they conceive, said the March of Dimes' Christopher Howson.
But all those factors explain only a portion of preterm birth. NIH's Spong pointed to efforts to understand how vaginal infections and inflammation may help trigger preterm labor.
Another mystery: Why African-American women are at higher risk, with a preterm birth rate of about 17 percent compared to under 11 percent among white women, Howson said.
Still, many women don't know that there are some protections, said Nikki Fleming of suburban Charlotte, N.C., who benefited from two of the steps recommended in Thursday's report and tries to spread the word.
Fleming's first baby, Lauren, was born at 26 weeks, weighing just over 2 pounds and spending her first five months in the hospital. Fortunately Lauren, now a healthy 8-year-old, fared well. But Fleming's next pregnancy ended in a miscarriage.
Her doctor determined that she would benefit from that cervical stitch as well as the progesterone shots. The result: two healthy full-term babies.
"I appreciate that they didn't treat it like an isolated incident," Fleming said.