Neural tube defects are abnormalities that can occur in the brain, spine, or spinal column of a developing embryo and are present at birth (birth defects).

Very early in the development of an embryo, certain cells form a tube (called the neural tube) that will later become the spinal cord, the brain, and the nearby structures that protect them, including the backbone (also called the spinal column or vertebra). As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. A neural tube defect occurs when this tube does not close completely somewhere along its length, resulting in a hole in the spinal column or another type of defect. These defects occur in the first month of pregnancy, often before a woman even knows that she is pregnant.