The United States has a higher infant mortality rate than any of the other 27 wealthy countries, according to a new report from the Centers for Disease Control. A baby born in the U.S. is nearly three times as likely to die during her first year of life as one born in Finland or Japan. That same American baby is about twice as likely to die in her first year as a Spanish or Korean one.

Despite healthcare spending levels that are significantly higher than any other country in the world, a baby born in the U.S. is less likely to see his first birthday than one born in Hungary, Poland or Slovakia. Or in Belarus. Or in Cuba, for that matter.

The U.S. rate of 6.1 infant deaths per 1,000 live births masks considerable state-level variation. If Alabama were a country, its rate of 8.7 infant deaths per 1,000 would place it slightly behind Lebanon in the world rankings. Mississippi, with its 9.6 deaths, would be somewhere between Botswana and Bahrain.

We're the wealthiest nation in the world. How did we end up like this?

New research, in a draft paper from Alice Chen of the University of South California, Emily Oster of the University of Chicago, and Heidi Williams of MIT, offers up some clues. They note that the infant mortality gap between the U.S. and other wealthy nations has been persistent -- and is poorly understood.

One factor, according to the paper: "Extremely preterm births recorded in some places may be considered a miscarriage or still birth in other countries. Since survival before 22 weeks or under 500 grams is very rare, categorizing these births as live births will inflate reported infant mortality rates (which are reported as a share of live births)."

Oster and her colleagues found that this reporting difference accounts for up to 40 percent of the U.S. infant mortality disadvantage relative to Austria and Finland. This is somewhat heartening.

But what about that other 60 percent?

"Most striking," they write, "the US has similar neonatal mortality but a substantial disadvantage in postneonatal
mortality" compared to Austria and Finland. In other words, mortality rates among infants in their first days and weeks of life are similar across all three countries. But as infants get older, a mortality gap opens between the U.S. and the other countries, and widens considerably. You can see this clearly in the chart below.


Digging deeper into these numbers, Oster and her colleagues found that the higher U.S. mortality rates are due "entirely, or almost entirely, to high mortality among less advantaged groups." To put it bluntly, babies born to poor moms in the U.S. are significantly more likely to die in their first year than babies born to wealthier moms.


In fact, infant mortality rates among wealthy Americans are similar to the mortality rates among wealthy Fins and Austrians. The difference is that in Finland and Austria, poor babies are nearly as likely to survive their first years as wealthy ones. In the U.S. - land of opportunity - that is starkly not the case: "there is tremendous inequality in the US, with lower education groups, unmarried and African-American women having much higher infant mortality rates," the authors conclude.

One way of understanding these numbers is by noting that most American babies, regardless of socio-economic status, are born in hospitals. And while in the hospital, American infants receive exceedingly good care - our neo-natal intensive care units are among the best in the world. This may explain why mortality rates in the first few weeks of life are similar in the U.S., Finland and Austria.

But the differences arise after infants are sent home. Poor American families have considerably less access to quality healthcare as their wealthier counterparts.

One measure of the Affordable Care Act's success, then, will be whether it leads to improvements in the infant mortality rate. Oster and her colleagues note that Obamacare contains provisions to expand post-natal home nurse visits, which are fairly common in Europe.

Research like this drives home the notion that economic debates in this country - about inequality, poverty, healthcare - aren't just policy abstractions. There are real lives at stake.