Spina bifida is the common name for a range of birth defects caused by problems with the early development of the spine. The main defect of spina bifida is an abnormal opening in the spinal column through which the spinal cord passes. This leaves the spinal cord unprotected and vulnerable to either injury or infection.

Spina bifida occurs in one of every 700 births to whites in North America, but only one in every 3,000 births to blacks. In some areas of Great Britain, the occurrence of spina bifida is as high as one in every 100 births, leading to the hypothesis that some environmental factors must be at work.

The classic defect of spina bifida is an opening in the spine, obvious at birth, out of which protrudes a fluid-filled sac. This sac may include either just the membranes which cover the spinal cord or the membranes plus...