Spina bifida and anencephaly affect approximately 1 in 1000 pregnancies in the US.[4]Cragan JD, Robert HE, Edmonds LD, et al. Surveillance for anencephaly and spina bifida and the impact of prenatal diagnosis - United States, 1985-1994. MMWR CDC Surveill Summ. 1995;44:1-13.
http://www.cdc.gov/mmwr/preview/mmwrhtml/00038567.htm
http://www.ncbi.nlm.nih.gov/pubmed/7637675?tool=bestpractice.com
Incidence and prevalence trends reveal striking differences in racial and ethnic susceptibility, with highest rates noted among Hispanic women and lowest rates noted among African and Asian women.[5]Mitchell LE. Epidemiology of neural tube defects. Am J Med Genet C Semin Med Genet. 2005;135C:88-94.
http://www.ncbi.nlm.nih.gov/pubmed/15800877?tool=bestpractice.com
[6]Centers for Disease Control and Prevention. Racial/ethnic differences in the birth prevalence of spina bifida - United States, 1995-2005. MMWR Morb Mortal Wkly Rep. 2009;57:1409-1413.
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5753a2.htm
http://www.ncbi.nlm.nih.gov/pubmed/19129744?tool=bestpractice.com
[7]Shin M, Besser LM, Siffel C, et al; Congenital Anomaly Multistate Prevalence and Survival Collaborative. Prevalence of spina bifida among children and adolescents in 10 regions in the United States. Pediatrics. 2010;126:274-279.
http://www.ncbi.nlm.nih.gov/pubmed/20624803?tool=bestpractice.com
Genetic susceptibility is a known factor. The birth of a first child with myelomeningocele raises the risk for a second child with myelomeningocele to 5%; having 2 children with myelomeningocele leads to a 15% risk that a third child will be affected.[5]Mitchell LE. Epidemiology of neural tube defects. Am J Med Genet C Semin Med Genet. 2005;135C:88-94.
http://www.ncbi.nlm.nih.gov/pubmed/15800877?tool=bestpractice.com
That said, more than 95% of infants with spina bifida are born to couples without a family history of neural tube defects. Therefore, environmental factors are also implicated. Geographical variability has been documented, with higher incidence rates noted in Northern China, England and Wales, and along the eastern seaboard in the US. Interaction between environmental and genetic factors is evidenced by temporal trends, seasonal variation, and fluctuations in the incidence of spina bifida with migration.[8]Olney RS, Mulinare J. Trends in neural tube defect prevalence, folic acid supplementation, and vitamin supplement use. Semin Perinatol. 2002;26:277-285.
http://www.ncbi.nlm.nih.gov/pubmed/12211618?tool=bestpractice.com
Spina bifida is 1.2 to 1.7 times more common in girls, except for sacral-level defects, which occur with equal frequency among boys and girls.[9]Lary JM, Edmonds LD. Prevalence of spina bifida at birth - United States, 1983-1990: a comparison of two surveillance systems. MMWR CDC Surveill Summ. 1996 Apr 19;45(2):15-26.
http://www.cdc.gov/mmwr/preview/mmwrhtml/00040954.htm
http://www.ncbi.nlm.nih.gov/pubmed/8602137?tool=bestpractice.com
Thoracic-level spina bifida is less common than lower-level lesions, and disproportionately affects girls.[10]Greene WB, Terry RC, Demasi RA, et al. Effect of race and gender on neurological level in myelomeningocele. Dev Med Child Neurol. 1991;33:110-117.
http://www.ncbi.nlm.nih.gov/pubmed/2015978?tool=bestpractice.com
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