Spina bifida and anencephaly affect approximately 1 in 1000 pregnancies in the US. 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. 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. 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. 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. Thoracic-level spina bifida is less common than lower-level lesions, and disproportionately affects girls.
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