Lack of oxygen in the blood supply, also called oxygen starvation.

This term is used to describe a deficiency in, or blockage of, the supply of oxygen in the body. Although not common, anoxia may occur during any stage of fetal development, infancy, or throughout life. In utero, the fetus may experience anoxia due to a variety of problems related to the mother's pregnancy. During prolonged labor and difficult birth, neonates (newborn infants) may experience a brief (or sometimes prolonged) cut-off of the supply of oxygen due to such developments as premature separation of the placenta during birth. The growing infant and child are at risk of anoxia mostly in accident-type situations such as choking, near-drowning, and near-suffocation. High fever may also result in anoxia, although this is rare. In extreme cases, anemia may cause the blood to be ineffective at carrying adequate oxygen to the body's tissues and organs.

The brain is among the organs most susceptible to oxygen starvation. When the brain is affected by anoxia, the special term hypoxia is applied. If the brain receives too little oxygen, developmental disorders and related learning disabilities may result.