Epidemiology

The estimated prevalence of spina bifida and anencephalus in the US is 3.63 and 2.15, respectively, per 10,000 live births.[3]

Incidence and prevalence trends reveal striking differences in racial and ethnic susceptibility, with highest rates noted among Hispanic women and lowest rates noted among Asian women.[4][5][6]

Genetic susceptibility is a known factor. The recurrence rate of neural tube defects, for women who have had one previous affected pregnancy, is 3% to 4%.[7][8][9] If two previous pregnancies have been affected, the recurrence rate is 10% to 20%.[10][11] However, 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.

Geographic variability has been documented, with higher incidence rates noted in Northern China, Central and South America, and Sub-Saharan Africa.[12]​ Interaction between environmental and genetic factors is evidenced by temporal trends, seasonal variation, and fluctuations in the incidence of spina bifida with migration.[13]

Spina bifida occurs with equal frequency among boys and girls.[12] Thoracic-level spina bifida is less common than lower-level lesions, and disproportionately affects girls.[14]

A worldwide decline in neural tube defect births has occurred over the past half-century.[6][12][15] Since the advent of alpha-fetoprotein screening and ultrasonography it is estimated that elective termination of pregnancy has diminished the birth incidence of anencephaly by 60% to 70%, and of spina bifida by 20% to 30%.[16] Rates of neural tube defects in the US have dropped 35% since the Food and Drug Administration (FDA)-mandated fortification of enriched cereal grain products in 1998, and the incidence of myelomeningocele has stabilized at 3.4 cases per 10,000 births.[17][18][19] However, many countries do not mandate fortification, due to concerns about the risks from high intakes of folic acid.[20][21] Excess folate may increase the risk of cognitive impairment and anemia in older adults with vitamin B12 deficiency.[22] Concern also exists that fortification may increase the risk of colorectal cancers.[23][24]

In countries where fortification has been implemented, prevention campaigns are increasingly focused on high-risk populations, including Hispanic women, women with diabetes, and women who are obese. These risk factors appear to have a synergistic effect.[25][26]​ For example, maternal obesity is associated with a 3.5-fold excess risk of having a baby with spina bifida.[27] This risk is increased 8-fold for a Hispanic woman with obesity, and is even higher if she also has diabetes.[28]

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