By MayoClinic. 2010. Definition Spina bifida is part of a group of birth defects called neural tube defects. The neural tube is the embryonic structure that eventually develops into the baby's brain and spinal cord and the tissues that enclose them. Normally, the neural tube forms early in the pregnancy and closes by the 28th… Continue reading Spina bifida — Overview of symptoms, causes and treatment of this serious birth defect.