1. Podulka J Stranges E Steiner C Statistical brief #110: hospitalizations related to childbirth, 2008. AHRQ; April 2011 http://www.hcup-us.ahrq.gov/reports/statbriefs/sb110.pdf
2. Martin JA Hamilton BE Ventura SJ Osterman MJ Mathews TJ Births: final data for 2011. CDC. NVSR 2013 62 1 http://www.cdc.gov/nchs/data/nvsr/nvsr62/nvsr62_01.pdf
3. An overview of distribution of births in United States hospitals in 2008 with implications for small volume perinatal units in rural hospitals;Simpson;J Obstet Gyneco Neonatal Nurs,2011
4. Zhao L Why are fewer hospitals in the delivery business? Working paper #2007-04. The Walsh Center for Rural Health Analysis; 2007 http://www.norc.org/PDFs/Walsh%20Center/Links%20Out/DecliningAccesstoHospitalbasedObstetricServicesinRuralCounties.pdf
5. Volume/outcome relationships in small rural hospitals;Schlenker;J Rural Health,1996