So why is our infant mortality so bad?

I know I’m a little late to this party, but I have an ongoing interest in infant mortality, so I’m going to cover it.

Everyone knows that in international comparisons, the infant mortality rate in the US is terrible. Some people think it’s because we code things differently and try harder to save premature babies. Others think that’s not true, and that this points to other problems in the health care system.

As always, though, it’s probably a mixture of many things. A new NBER working paper gets at just that. “Why is Infant Mortality Higher in the US than in Europe?”

The US has a substantial – and poorly understood – infant mortality disadvantage relative to peer countries. We combine comprehensive micro-data on births and infant deaths in the US from 2000 to 2005 with comparable data from Austria and Finland to investigate this disadvantage. Differential reporting of births near the threshold of viability can explain up to 40% of the US infant mortality disadvantage. Worse conditions at birth account for 75% of the remaining gap relative to Finland, but only 30% relative to Austria. Most striking, the US has similar neonatal mortality but a substantial disadvantage in postneonatal mortality. This postneonatal mortality disadvantage is driven almost exclusively by excess inequality in the US: infants born to white, college-educated, married US mothers have similar mortality to advantaged women in Europe. Our results suggest that high mortality in less advantaged groups in the postneonatal period is an important contributor to the US infant mortality disadvantage.

The paper is wonky, but it uses comprehensive data to compare births in the US to births in Austria and Finland. According to table 1, the infant mortality rate was 6.8 per 1000 births in the US, 4.0 per 1000 births in Austria, and 3.2 per 1000 births in Finland. If they used a restricted sample of births of at least 22 weeks gestation and 500 g then the infant mortality became 4.6 per 1000 births in the US, 2.9 per 1000 births in Austria, and 2.6 per 1000 births in Finland.

They considered four different explanations for these differences: reporting differences, conditions at birth, neonatal mortality, and postneonatal mortality. What did they find?

Reporting differences (the favorite explanation of those defending the US healthcare system from the infant mortality metric attack) explained up to 40% of the disadvantage in US infant mortality. But that would only get us closer. It would still leave us way worse. Worse conditions at birth accounted for 30% of the remaining difference compared to Austria, but 75% of the remaining difference compared to Finland.

More concerning, though, is that our neonatal mortality (or the mortality in the first month of life) wasn’t so different than the other countries. What accounted for the real disadvantage was postneonatal mortality, or mortality from one month to one year of age. That difference was almost entirely due to excess inequality in the US.

In other words, most of the infant mortality difference between the US and other countries was due to really high postneonatal mortality in less advantaged groups. If differences were due to neonatal mortality, then you would want to try and reduce preterm births. That’s often what we’ve been trying to do. But this study shows us that this isn’t where the lesion is. It’s in the postneonatal period. (This point is consistent with Austin’s latest post about NICUs on the JAMA Forum.)  It’s possible that the inpatient care is excellent right after birth, but once babies go home, their access to care is different along socio-economic lines. To fix that, you likely need to improve the health care system, or inequality in the US.

So there are two main takeaways from this paper. The first is that although reporting differences can account for some of our worse infant mortality statistics, most of the differences we see are not due to that explanation. The second is that most of the rest of the disadvantage is due to differences in postneonatal mortality, that likely require fixes to the healthcare system. Whether the ACA does so remains to be seen.



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