What is the primary cause of spina bifida?

Spina bifida primarily results from a neural tube defect that occurs during early embryonic development, specifically within the first few weeks of pregnancy. The neural tube is a structure that eventually develops into the brain and spinal cord. In spina bifida, the neural tube does not close completely, leading to an incomplete formation of the spine and the surrounding structures. This defect is critical because it can lead to a range of physical and neurological problems depending on the severity and location of the defect.

While other factors like genetic mutations, infections during pregnancy, and vitamin deficiencies can contribute to the risk of neural tube defects, they are not the primary cause of spina bifida itself. For instance, while folic acid (a vitamin) deficiency is associated with an increased risk of neural tube defects and hence spina bifida, it is the failure of the neural tube to close properly that constitutes the actual defect leading to the condition.