What's behind the high rate of infant deaths in the U.S.

Why are babies in the U.S. more likely to die than infants in comparably wealthy countries?

That's the question economists set out to answer in a recent working paper, citing statistics showing that the U.S. ranks No. 56 in the world in rates of infant mortality, or much lower than considerably poorer countries. Their answer: economic inequality and poverty.

"When we compare relatively advantaged women in the U.S. to similarly advantaged women in Finland and Austria, we see they have similar levels of infant mortality," said Emily Oster, an associate professor of economics at the University of Chicago Booth School of Business and one of the study's co-authors, by email. "However, when we compare the remainder of the distribution, the U.S. has much higher infant mortality."

In other words, infants are more likely to die if their parents are poor and more likely to live if they were lucky enough to be born to richer parents.

Roughly six infants in 1,000 die in the U.S. before they turn one-year-old. That is roughly three times higher than in Japan, which has the second-lowest rate of infant mortality (Monaco, the uber-wealthy principality in Europe, ranks No. 1.) Put another way, that means three more infants out of 1,000 die in the U.S. compared with in Finland, which the authors examined in the study, and in other Scandinavian countries (They also looked at Austria because it has a similar rate of infant mortality to the rest of Europe.)

Most explanations of why the U.S. compares poorly to so many other countries in infant mortality have focused on health, not wealth. If infants were more likely to die in America, under this view, that was chiefly because of the higher rate of pre-term births. Researchers pointed to such factors as gestational age and birth weight in proposing that health is the main driver of infant deaths in the U.S.

But while those factors do, in fact, contribute to infant mortality, they don't tell the whole story, said Oster, who co-wrote the paper with economist Alice Chen of the University of Southern California and Heidi Williams, an economist at the Massachusetts Institute of Technology. For instance, they note that even U.S. infants with a normal birth rate have a higher rate of death than babies in Europe. Something else must be at work.

America's racial and ethnic make-up is also often posited to explain why infant deaths are more common in America than in many other countries. And notably, black infants in the U.S. are more likely to die than white infants, largely because of health differences at birth. But infant mortality is higher in this country even if African-Americans are excluded from the analysis, the researchers note. So while race clearly factors into the discussion, it also fails to fully explain the death gap between the U.S. and European nations.

To truly understand why more babies are likely to die in the America, it's necessary to zero in on their socioeconomic status, the researchers say. And here they find something remarkable: U.S. infants actually have a lower mortality rate, and appear healthier by some measures, in the first month of their lives than infants in Austria or Finland. But that advantage disappears as babies get older. For infants older than one month, U.S. infant mortality is much higher than in Europe.

What accounts for that change? "This postneonatal mortality disadvantage is driven almost exclusively by excess inequality in the U.S." Chen, Oster and Williams write.

The researchers also underscore that the health of infants older than a month is as important as the health of babies at birth in understanding why the U.S. trails Europe rankings of infant deaths.

One reason this distinction between younger and older infants is important is that the causes of death for each group are very different. While newborn deaths are more likely to be linked to health problems, older infants are more vulnerable to accidents and Sudden Infant Death Syndrome. Meanwhile, if the high infant mortality rate in the U.S. owes largely to what happens to slightly older babies, then offering more high-tech medical care at birth is unlikely to remedy the problem.

"[T]he facts documented here suggest that, in general, if the goal is to reduce infant mortality, then policy attention should focus on either preventing preterm births or on reducing postneonatal mortality," the researchers write.

What can be done to reduce infant mortality in the U.S.? One possible approach would be to have nurses or other health professionals visit parents and infants at home, the economists suggest. That practice is common in Europe, but fairly rare in the U.S.

More broadly, the implications of the study are clear. Inequality starts at birth, and the condition can be fatal.

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    Alain Sherter covers business and economic affairs for CBSNews.com.