The study cited is a guesstimate, because they simply don't have one-month data to work from.
One of the issues in the US is that we have much higher infant mortality among certain populations.
We also have other social ills, like drug addiction. Low birth weight infants are particularly at risk. The preterm birth issue I think is real, because the CDC thinks so:
http://www.cdc.gov/nchs/data/databriefs/db09.htmIn 2005, 68.6% of all infant deaths occurred to preterm infants, up from 65.6% in 2000.
Very preterm infants accounted for only 2% of births, but over one-half of all infant deaths in both 2000 and 2005. Because the majority of infant deaths occur to very preterm infants, changes in either the percentage of these infants or in their infant mortality rate can have a large impact on the overall infant mortality rate.
The infant mortality rate for very preterm infants was 183.24 infant deaths per 1,000 live births in 2005, not significantly different from the rate in 2000 (180.94), halting a long-term decline (1,2).
The plateau in the U.S. infant mortality rate from 2000 to 2005 was largely due to the combination of the increase in the percentage of very preterm births and the lack of decline in the infant mortality rate for these births. However, the increase in the percentage of late preterm births has also had an impact. In 2005, the infant mortality rate for late preterm births was three times that for term births (37-41 weeks) (1)
![](http://www.cdc.gov/nchs/data/databriefs/db09_fig5.gif)
One interesting aspect of the US failure to make progress is that premature birth rates are much higher among women of African genetic heritage, and it probably isn't due to anything in the US, because the rates between the UK and US are very comparable for this group.
Here's a study on the issue - we need to do more work on this. If we could find an address the causes of this excess premature birth rate, our infant mortality rate would look much more like that of Sweden.
http://www.emekmed.com/pictures/files/Epidemiology%20and%20causes%20of%20preterm%20birth.pdfI've read studies attributing premature births to everything from stress to smoking, but at least in the US, black women have lower smoking rates than other groups with much lower premature birth rates. The huge disparity in preterm birth rates is very frustrating, and it is worth while putting a lot more money into it:
In the USA and in the UK, women classified as black, African-American, and Afro-Caribbean are consistently reported to be at higher risk of preterm delivery: preterm birth rates are in the range of 16–18% in black women compared with 5–9% for white women. Black women are also three to four times more likely to have a very early preterm birth than women from other racial or ethnic groups.22,23 Part of the discrepancy in preterm birth rates between the USA and other countries might be explained by the high rate of preterm births in the USA black population. Over time, the disparity in preterm birth rates between black and white women has remained largely unchanged and unexplained, and contributes to a cycle of reproductive disadvantage with far-reaching social and
medical consequences.24