📖 Definition
A type of neural tube defect that occurs when the spinal column does not close completely during fetal development (around 3–4 weeks after conception). It ranges from mild (spina bifida occulta, often symptomless) to severe (myelomeningocele, where the spinal cord protrudes through the back). Adequate folic acid before and early in pregnancy significantly reduces risk. Prenatal detection is possible via AFP screening and ultrasound.