Each day, more than 3,000 children under age 5 die from preterm birth complications—meaning that, for the first time ever, premature birth is the biggest killer of young children around the globe.

A new study in the Lancet finds that of the 1.1 million such deaths in 2013, 965,000 of them were a direct result of being born too early, with the child dying within 28 days of birth.

But another 125,000 deaths happened between the age of 1 month and 5 years, according to a press release. Meanwhile, the overall mortality rate for children under 5 has declined since 2000, as vaccines, antibiotics, and other advances have reduced deaths from pneumonia, measles, and other causes.

"The success we've seen in the ongoing fight against infectious diseases demonstrates that we can also be successful if we invest in prevention and care for preterm birth," says a researcher.

The first step, which is already underway with $250 million in new funding: Figure out what causes preterm births. Obesity, high blood pressure, and later-in-life motherhood are all risk factors, but the exact trigger for premature labor remains a "mystery," the Telegraph reports.

The countries most affected are often poor: India has the highest number of deaths from preterm birth complications, followed by Nigeria and Pakistan. But even in the US, 28% of under-5 deaths are caused by such complications, which is above the global average of 17.4%; the US has "one of the worst preterm birth rates of any high-resource country," the press release notes.

Among the new research initiatives: identifying the electric signals that trigger labor and figuring out whether that process is initiated by the mother or the fetus.

(A dad singing to his premature baby boy recently went viral in a heartbreaking video.)

This article originally appeared on Newser: Biggest Killer of Kids Under 5: Premature Birth

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