1. Etiologies of preterm birth in an indigent population: is prevention a logical expectation?;Tucker;Obstet Gynecol,1991
2. Epidemiologic characteristics of preterm delivery: etiologic heterogeneity;Savitz;Am J Obstet Gynecol,1991
3. Preventing preterm birth: are we making any progress?;Kramer;Yale J Biol Med,1997
4. Births: final data for 2008;Martin;Natl Vital Stat Rep,2010
5. Births: preliminary data for 2009;Hamilton;Natl Vital Stat Rep,2010