References
Blencowe H, Cousens S, Oestergaard MZ et al. (2012) National, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications. Lancet 379, 2162-2172.
Burris HH & Collins JW, Jr. (2010) Race and preterm birth--the case for epigenetic inquiry. Ethn Dis 20, 296-299.