The blood and nutrients reach the baby through the umbilical cord.
Intrauterine hypoxia may be due to problems in the umbilical cord such as cord prolapse (when the cord exits before the baby during delivery) /occlusion (this is when the cord gets trapped between the baby and the birth canal, causing blockage of blood supply to the baby), placental infarction (death of placental tissue because not enough blood reaches it) and maternal smoking. Intrauterine growth restriction (IUGR), when the baby is born small, may cause or be the result of hypoxia. Birth asphyxia may result due to prolonged labor (more than 18 hours), breech delivery in full-term infants (baby's feet come out before the head); placental abruption (the placenta separates from the uterus) , and maternal sedation in premature infants.
Oxygen deprivation is the most common cause of perinatal brain injury.
Intrauterine hypoxia and birth asphyxia can cause hypoxic ischemic encephalopathy where the brain and spinal cord are injured from inadequate oxygen, leading to an increased mortality rate, including an increased risk of Sudden infant death syndrome (SIDS). Oxygen deprivation in the fetus and neonate have been pointed out to be as either the leading cause or as contributing risk factors in many neurological disorders such as epilepsy, ADHD (attention deficit-hyperactivity disorder), and cerebral palsy.