Differences in how live births are recorded may affect international IMR comparisons; however,
it is unlikely that these recording differences would entirely explain the high U.S. IMR or the
variation between the U.S. IMR and those of some European countries. This is because of both
the widespread use of the WHO definition of live births and the small number of births that fall
outside the WHO definition.25 Researchers at NCHS conclude that for recording differences to
completely explain the high U.S. IMR, European countries would have to misreport one-third of
their infant deaths, which these researchers conclude is unlikely.
After adjusting for recording differences, NCHS researchers found that the U.S. IMR was still
higher than those in most European countries. Specifically, these researchers excluded deaths that
occurred prior to 22 weeks of gestation. They found that excluding these very short gestational
age births lowered the U.S. IMR to 5.8 (in 2004), but also lowered the IMR of European
countries; therefore, it changed the U.S. ranking compared to European countries by only a small
amount.26 Given this finding, the NCHS researchers conclude that recording differences can
explain only a small percentage of international IMR variation and do not entirely explain why
the U.S. IMR is higher than the rates of a number of European countries.