What’s killing American babies before their first birthday?

(Bloomberg) — The number of infants who die before their first birthday is an important measure of a nation’s health, and the U.S. performs poorly. This isn’t just compared with Western Europe. The U.S. ranks below dozens of other countries, including Cuba, Lithuania and South Korea, by one measure.

It’s difficult to untangling the reasons behind the gap in infant mortality, or even the extent of the problem. Nations measure and report births and deaths in different ways. For instance, a death shortly after delivery that is counted toward the tally in the U.S. may be excluded as a stillbirth elsewhere.

See also: The poor still die young, but their kids have hope

A new economic paper attempts to explain some of this dissonance. Differences in reporting methodology do inflate America’s infant mortality rate, compared with those in some countries, economists from Brown University, the University of Southern California, and Massachusetts Institute of Technology found. But that’s not the whole story.

When they compared data on U.S. births with those in Austria and Finland — two countries with similarly detailed reporting — the authors found that America’s mortality rate deviated after the first month of life.

In other words, American infants are more likely to die between one month and one year than babies in Austria and Finland. “We know something’s happening after the baby leaves the hospital,” said Alice Chen, a health economist at USC and co-author of the paper. “It’s happening mostly among low socioeconomic groups.”

One theory is that European systems provide more social support for new mothers, often including home visits by nurses or other professionals in the first months after birth. (Finns famously get a gift package from the government upon the arrival of a new child.)

David Olds has spent decades studying just such interventions. A professor of pediatrics at the University of Colorado, he’s led long-term randomized control trials to measure the effect of nurse visits targeted to disadvantaged mothers from pregnancy to age two. Studies in Elmira, N.Y., Memphis, and Denver, have found some health and social benefits for families, including reductions in infant mortality.

Olds is founder of the Nurse-Family Partnership, which provides such services to about 33,000 families in the U.S. He estimates that the need for them is in the hundreds of thousands. Poverty and troubled circumstances can make it challenging to provide safe environments for children, he said. “If the mother is living in a household where she is essentially homeless, and she’s there couch-surfing with a newborn baby, her ability to protect that child is really limited,” Olds said.

The Affordable Care Act created a federal home visit program, currently funded at about $400 million a year. The program served more than 145,000 parents and children in the 2015 fiscal year, according to the Health Resources Services Administration.

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