Cerebral palsy is caused by a problem in the parts of the brain responsible for controlling movement. It can occur if the brain is damaged in early life or develops abnormally, although the exact cause is not always obvious.

Parts of the brain responsible for other important functions  such as communication, hearing, vision and the ability to learn  may also be affected. This is why people with the condition can have various other problems, not just ones involving the muscles.

What causes the problems in the brain?

In the past, doctors believed that cerebral palsy was caused by brain damage sustained during birth  the direct result of being temporarily deprived of oxygen (asphyxiation). Asphyxiation can sometimes occur during a difficult or complicated birth.

However, a major research project carried out in the 1980s showed that asphyxiation was only responsible for up to 1 in 10 cases of cerebral palsy. Most were due to problems with the brain that developed before the child was born.

Researchers believe there are three main problems that can affect the brain before birth and cause cerebral palsy. These are discussed below.

Periventricular leukomalacia (PVL)

Periventricular leukomalacia (PVL), also known as white matter damage of immaturity, refers to damage of the brain's white matter. This part of the brain comprises many nerve fibres, which are protected by a white fatty protein, known as myelin. The white matter is responsible for directing communication between the thought-processing sections of the brain (known as grey matter) and the rest of the body.

It is thought the brain damage is caused by a reduction in the child’s blood or oxygen supply, which damages the brain cells. This has serious consequences in later life, as the white matter is responsible for transmitting signals from the brain to the muscles.

It is not clear exactly why PVL occurs, but it has been linked to:

  • an infection caught by the mother
  • the mother having abnormally low blood pressure  for example, due to a caesarean section
  • premature birth, especially if a child is born at 32 weeks of pregnancy or earlier

Abnormal development of the brain

Anything that changes or affects the brain's normal development can lead to problems with the way it transmits information to the muscles. If this happens, a child can develop cerebral palsy.

Brain development can be affected by:

  • changes (mutations) in the genes that play a role in the brain's development
  • an infection caught by the mother
  • trauma or injury to the unborn baby's head

Intracranial haemorrhage and stroke

Intracranial haemorrhage is bleeding in the brain. This can be dangerous because the brain can be deprived of blood, which can cause parts of the brain to die – the build-up of blood itself can damage brain tissue.

Intracranial haemorrhage is normally seen in babies born prematurely, although it sometimes occurs in unborn babies after they have had a stroke. Factors that increase the risk of an unborn baby having a stroke include:

  • pre-existing weaknesses or abnormalities in the baby's blood vessels or the mother’s placenta
  • high blood pressure in the mother
  • the mother having an infection during pregnancy, particularly pelvic inflammatory disease (an infection of the female upper genital tract)

Brain damage during or after birth

A few cases of cerebral palsy are caused by brain damage that occurs during or soon after birth.

The damage normally occurs during the first few months of a baby’s life, before the brain develops its ability to withstand and adapt to a moderate degree of damage.

Damage can be caused by asphyxiation when the child is born, an infection of the brain (such as meningitis), a particularly low blood sugar level, a serious head injury or a stroke.