One of the first parts of the body to develop is the central nervous system. The neural tube, from which the spinal cord and brain develop, is formed within the first 25 to 28 days of pregnancy. Spina Bifida is caused by the failure of the neural tube to develop properly, hence the term 'neural tube defects'. Related defects are anencephaly (the absence of a brain) and encephalocele (a malformation of the brain and skull).
The human nervous system develops from a small, specialized plate of cells along the back of an embryo. Early in development, the edges of this plate begin to curl up toward each other, creating the neural tube—a narrow sheath that closes to form the brain and spinal cord of the embryo. As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. This process is usually complete by the 25th to the 28th day of pregnancy. But if problems occur during this process, the result can be brain disorders called neural tube defects, including spina bifida.