About eight per cent of babies born in Canada each year arrive too soon. (Claude Paris/Associated Press)

For all the miracle stories of tiny preemies who survive, the sad reality is that scientists know far too little about what triggers premature birth and how to prevent it.

And despite some recent progress, the U.S. has a far higher rate of preterm births than other similar nations.

On Thursday, an international coalition said there are a handful of proven protections — and if the U.S. and other developed countries do a better job of using them, together they could keep 58,000 babies a year from being born too soon.

That's a blip in the global epidemic of prematurity: About 15 million preterm babies are born every year, most of them in Africa and parts of Asia where the priority is to improve care of these fragile newborns. More than 1 million premature infants die, mostly in developing countries, and survivors can suffer lifelong disabilities.

But in wealthier countries, where sophisticated medical care already keeps most preemies alive, the focus is shifting to how to prevent these births in the first place. Nearly 1 in 10 births across the developed world are preterm, and about 1 in 8 in the U.S. Only recently have rates begun levelling off or dropping in many of these countries after years of steady increases.

Thursday's report makes clear just how hard additional progress on that front will be — projecting an average 5 per cent drop in preterm birth rates across the highest-income countries by 2015, if they follow the new advice.

Healthier babies, healthier adults

"Shockingly, very little reduction is currently possible," specialists with the World Health Organization, Save the Children, U.S. National Institutes of Health, March of Dimes and other groups reported in The Lancet.

But even that improvement would translate into about $3 billion US in annuals savings from medical bills and lost productivity, the group calculated. Nearly half that savings would be in the U.S.

The bigger message: It's time for a major scientific push to figure out the causes of preterm birth and find some better ways to intervene.

"I don't think it's hopeless at all," said report co-author Dr. Catherine Spong, a maternal-fetal medicine specialist at NIH who points to clues that infections and inflammation affecting the mother play a yet-to-be-understood role.

Because healthier babies grow into healthier adults, "if you could improve pregnancy outcomes, you could improve the health of the nation, quite honestly," she added.

Over half a million U.S. babies are born premature, before completion of the 37th week of pregnancy. That's 11.7 per cent of the babies born in 2011, the lowest rate of preterm birth in a decade and down from a peak of 12.8 per cent in 2006, the March of Dimes reported earlier this week.

Contrast that with Japan and Sweden, where fewer than 6 per cent of births are premature, or Canada and Britain where fewer than 8 per cent are.

Last spring, this same international coalition provided the first country-by-country estimates of preterm births and recommended some inexpensive steps that developing countries could take to improve preemie survival. The latest follow-up analyzed trends in developed countries, to come up with advice on preventing prematurity.

The report recommends:

— Nearly eliminating the practice of inducing labour 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 per cent in Canada to 23 per cent in the U.S. and 30 per cent 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 per cent 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 per cent 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 per cent.

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 labour.

Another mystery: Why African-American women are at higher risk, with a preterm birth rate of about 17 per cent compared to under 11 per cent 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.