Premature births a big factor in high U.S. infant mortality rate

Despite recent progress in preventing the deaths of its youngest citizens, the United States’ infant mortality rate is fourth highest among 29 of the world’s most developed nations, a new report says.

With 6.1 infant deaths per every 1,000 live births in 2010, the U.S. mortality rate was more than double those of Finland (2.3), Japan (2.3), Portugal (2.5) and Sweden (2.5), according to a study published Wednesday by the Centers for Disease Control and Prevention. In addition to trailing most European countries, the U.S. also lagged behind South Korea, Israel, Australia and New Zealand in 2010, the most recent year for which international statistics were available.

The infant mortality rate measures deaths of babies before their first birthday. The United States recorded 23,985 such deaths in 2011, according to the CDC.

Some of the countries did not report deaths of extremely premature babies born only 22 or 23 weeks into a pregnancy. So the CDC researchers did a separate ranking that excluded births before 24 weeks of gestation.

The United States fared better in that analysis, with 4.2 infant deaths per 1,000 live births. That was lower than the rates for Poland and Northern Ireland (both 4.5), but still double the rate for Finland and Sweden (2.1).

The longer the gestation period, the more the U.S. lagged behind other developed countries. For instance, the U.S. mortality rate for babies born after 24 to 27 weeks was the fifth lowest. But for babies born after 32 to 36 weeks — the period during which most preterm births occur — the U.S. had the second-highest mortality rate. And for babies who made it to at least 37 weeks, the U.S. had the highest rate, at 2.2 deaths per 1,000 live births.

If the United States could reduce its mortality rate for this group of infants to the 1.1 rate of Sweden, the nation’s overall infant mortality rate would fall to 3.2 deaths per 1,000 live births. That translates into 4,100 fewer lives lost per year, according to the study.

In addition, if the U.S. could reduce the percentage of births involving premature infants (those born before 37 weeks) from 9.8% to the 5.8% of Sweden, its overall mortality would fall to 3.4. That would mean 3,200 fewer infant deaths per year.

The report did not address the reasons why so many American babies die during their first year of life. Other research from the CDC has found that five conditions — serious birth defects, premature births, Sudden Infant Death Syndrome, injuries and maternal complications during pregnancy — account for 58% of infant deaths in the U.S.

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