Washington ? They call it kangaroo care: A premature baby nestles skin-to-skin against mom’s bare, warm chest. In Malawi, mothers’ bodies take the place of too-pricey incubators to keep these fragile newborns alive.

Nearly one in 10 of the world’s babies is born prematurely, and about 1 million infants die each year as a result, says a startling first attempt to measure a toll that in much of the world is hidden.

It’s a problem concentrated in poor countries, with the vast majority of the nearly 13 million preemies born each year in Africa and Asia, according to the report released Sunday by the March of Dimes.

But take a closer look at the proportion of all babies born too early. Those rates are highest in Africa, but followed closely by North America, concludes the first part of a collaboration with the World Health Organization to tackle the growing problem.

How? “That’s the 13 million-baby question,” said March of Dimes epidemiologist Christopher Howson, who headed the project being debated this week at a child health meeting in India.

Different factors fuel prematurity in rich countries and poor ones. Scientists don’t even know all the triggers for preterm birth or how to stop early labor once it starts, one reason that the report urges major new research. Nor does much of the world even track how many babies are born too soon, why or what happens to them.