A condition present at birth in which a developing baby's spinal cord doesn't form properly.

In spina bifida, the spine and spinal cord of an unborn baby don't form as usual. As a baby develops during pregnancy, the neural tube becomes the brain, spinal cord and tissues that enclose them. In babies with spina bifida, a part of the neural tube doesn't close all the way.

Spina bifida can cause a sac filled with fluid and spinal nerves to form on the baby's back. Sometimes the sac doesn't contain nerves. It can affect bowel and bladder function and cause weakness or lack of movement in the legs. Fluid may build up in the brain. Or a baby may not have a sac or symptoms. A tuft of hair, dimple or birthmark may be on the back instead.

Prenatal tests can often diagnose spina bifida before birth, but some babies are diagnosed right after birth. Sometimes surgery to repair the unborn baby's spinal cord is done before birth while the baby is still in the womb. Other times, surgery is done within 72 hours of birth.