The neural tube lies along the back of a developing embryo and becomes the brain and spinal cord. Neural tube defects are abnormalities of the embryo's brain and spinal cord. The most common neural tube defect is a condition known as spina bifida. Spina bifida can be mild or severe. In mild forms, babies are born with a dimple or tuft of hair at the base of the spine. In more serious forms, the spinal bones (vertebrae) are abnormal or part of the spinal cord is open to the skin. Severe forms can cause weakness or numbness in the legs and lack of bladder or bowel control. Women who take folic acid vitamin supplements before and during early pregnancy are less likely to have babies with neural tube defects than women who do not take folic acid. In 1996, the USPSTF recommended that all women who could become pregnant take a multivitamin supplement containing folic acid. The USPSTF wanted to see whether new studies supported a change in the 1996 recommendation.