Scientists do not completely understand what causes most cases of cerebral palsy (CP). There may be a number of factors contributing to the disorder, but researchers believe that abnormal brain development during pregnancy (prenatal) may be responsible in most cases. A small number of cases are believed to be due to injury to the brain before, during or after birth (perinatal).

Possible causes that may occur during pregnancy include:

• Genetic or chromosomal disorders (thrombophilia) that lead to abnormal brain development.
  
  
• Intrauterine infection (infection that occurs in the womb) in the mother, including streptoccocal, syphilis and varicella infections.
  
  
• Systemic infection in the mother, including German measles (rubella).
  
  
• Premature birth. Babies born prematurely are at risk for a number of complications, including bleeding in the brain (intraventricular hemorrhaging or IVH) and brain damage (e.g., periventricular leukomalacia or PVL).
  
  
• Blood type incompatibility. Occurs when the blood Rh factor (positive or negative) between the fetus and mother are mismatched. However, this is unlikely to occur with modern prenatal care. Routine testing of Rh factor occurs during first trimester laboratory tests, and incompatibility is easily treated with immune globulin to prevent complications.  

Possible causes that may occur before, during and immediately after birth include:

• Perinatal asphyxia. Lack of oxygen to a baby’s brain (ischemia) and/or blood (hypoxia). This can be caused by a number of circumstances, including prolonged labor, umbilical cord or placental trauma, breech births, and multiple births. Multiple births are a particular risk if one twin dies in the uterus.
  
  
• Coagulation (blood-clotting) disorders that cause fetal strokes.
  
  
• Severe newborn jaundice (yellowing of the skin and eyes caused by excess buildup of the pigment bilirubin in the blood). Excessive amounts of bilirubin can kill brain cells in the basal ganglia (which controls motor skills) and brain stem, a condition called kernicterus.

Possible causes that may occur during the first two to three years of life include:

• Trauma. A brain injury from a fall, accident or from child abuse such as intentional shaking (shaken baby syndrome).
  
  
• Asphyxia. A near-drowning accident that deprives the brain of oxygen.
  
  
• Infection. Meningitis or encephalitis that damages brain tissue or attacks the child’s central nervous system.
  
  
• Brain tumors.

There are several factors generally recognized to increase the risk of a fetus, newborn or young child developing CP. They include:

• Labor and delivery complications. Any conditions that deprive the fetus or newborn of oxygen, blood or nutrients. This may include breech births, prolonged labor and physical birth defects in the newborn. Use of forceps or other instruments to pry the baby out of the birth canal increases the risk of trauma to the newborn’s brain. Placental abruption (when the placenta separates from the walls of the uterus) can disrupt the fetal oxygen supply if it occurs before birth.
  
  
• Maternal infection (e.g., German measles, cytomegalovirus and toxoplasmosis), especially during the first 6 months of pregnancy. Uterine or birth canal infections also increase the risk of placenta inflammation (chorioamnionitis) which can impede normal fetal brain development.