Pathophysiology

Spina bifida is caused by the failure of the neural tube to close during the first month of embryonic development (often before the mother knows she is pregnant).

Under normal circumstances, the closure of the neural tube occurs around the 23rd (rostral closure) and 27th (caudal closure) day after fertilization.^[40] However, if something interferes and the tube fails to close properly, a neural tube defect will occur. Medications such as some anticonvulsants, diabetes, having a relative with spina bifida, obesity, and an increased body temperature from fever or external sources such as hot tubs and electric blankets may increase the chances of delivery of a baby with a spina bifida.

Extensive evidence from mouse strains with spina bifida indicates that there is sometimes a genetic basis for the condition. Human spina bifida, like other human diseases, such as cancer,hypertension and atherosclerosis (coronary artery disease), likely results from the interaction of multiple genes and environmental factors.

Research has shown the lack of folic acid (folate) is a contributing factor in the pathogenesis of neural tube defects, including spina bifida. Supplementation of the mother's diet with folate can reduce the incidence of neural tube defects by about 70%, and can also decrease the severity of these defects when they occur. It is unknown how or why folic acid has this effect.

Spina bifida does not follow direct patterns of heredity like muscular dystrophy or haemophilia. Studies show a woman having had one child with a neural tube defect such as spina bifida has about a 3% risk of having another child with a neural tube defect. This risk can be reduced to about 1% if the woman takes high doses (4 mg/day) of folic acid before and during pregnancy. For the general population, low-dose folic acid supplements are advised (0.4 mg/day).