1. US census bureau http://www.census.gov/
2. CIA https://www.cia.gov
3. Shurtleff DB (2004) Epidemiology of neural tube defects and folic acid. Cerebrospinal Fluid Res 1:5
4. Peña A, Levitt MA (2005) Imperforate anus and cloacal malformations. In: Ashcraft KW, Holcomb GW, Murphy JP (eds) Pediatric surgery, 4th edn. W.B. Saunders, Philadelphia, pp 496–517
5. Lary JM, Edmonds LD (1996) Prevalence of spina bifida at birth—United States, 1983–1990: a comparison of two surveillance systems. MMWR CDC Surveill 45:15–26