Table 2 in the report cited shows clearly that U.S. is #3 in the world (behind Norway and Sweden) in infant mortality for babies born at 22-23 weeks and 24-27 weeks, #4 (behind Norway Sweden and Austria) for babies born between 28-31 weeks, and #3 (behind Austria and Norway) for babies born between 32-36 weeks http://www.cdc.gov/nchs/data/databriefs/db23.htm
My guess is that if you separated out White and Black infants (which in this country essentially means controlling for socioeconomic status), our rankings might well jump to #1 in every category.
Medical care matters way more for these preemies than for births in general (after all, low risk births can be safely delivered at home). That said, Scandinavian and Austrian women are “heartier stock” than the average American women, so at least some of the apparent survival advantage for these countries may lie in this physiological difference (which obviously has nothing to do with the quality of medical care in any of these countries and much more to do with lifestyle/exercise etc.).
I wonder what % are crack babies/meth babies. That does wonders for the unborn kids.