Cerebral palsy: Causes and risk factors

The term “cause” is self-explanatory. The term “risk factor” can be defined as “any attribute, characteristic, or exposure of an individual that increases the likelihood of developing a disease or injury”. Causes thus have a stronger relationship with CP than risk factors. Significant deprivation of oxygen to the infant’s brain, for example, is a cause of CP. Preterm birth is a risk factorbut not a cause of CP—in other words, not every preterm baby is found to have CP. There are many possible causes of brain injury, including events before and during pregnancy, during birth, or in early infant life. Much is known about the causes and risk factors for CP, but much remains unknown as well. Depending on what you read, you may come across different lists of causes and risk factors for CP.

Causes of CP

Developing fetuses and infants (up to age two to three) can develop CP if they experience brain injury or disruptions in brain development caused by:

  • Bleeding in the brain before, during, or after birth
  • Infections of the brain, including meningitis or encephalitis
  • Shock—a state in which organs and tissues do not receive adequate blood flow
  • Traumatic brain injuries, such as from a serious car accident
  • Seizures at birth or in the first month following birth
  • Certain genetic conditions

Risk factors for CP

Risk factors for CP include:

  • Preterm birth and low birth weight. A typical pregnancy lasts 40 weeks. Babies born before 37 weeks have a greater risk of having CP. The risk increases the earlier a baby is born and the lower the baby’s birth weight. Twins and other multiple-birth siblings are at particular risk because they tend to be born earlier and at lower birth weights.
  • Serious illness, stroke, or infection in the mother. CP is more common in children whose mothers: a) Experience certain viral and bacterial infections and/or high fevers during pregnancy. b) Have coagulation (clotting) disorders or experience blood clots during pregnancy. c) Receive excessive exposure to harmful substances during pregnancy. d) Have thyroid problems, seizure disorders, or other serious health concerns.
  • Serious illness, stroke, or infection in the baby. Infants who experience serious illnesses, strokes, or seizures around the time of birth are at greater risk of having CP. Such illnesses might include: a) Severe jaundice. (Kernicterus is a rare kind of preventable brain damage that can happen in newborns with jaundice.) b) Seizures during the first 48 hours after birth. c) Infections of the brain, such as meningitis or encephalitis. d) Strokes caused by broken or clogged blood vessels or abnormal blood cells.
  • Pregnancy and birth complications. For example, not enough nutrition through the placenta or a lack of oxygen during labor and birth. Incompatible blood types between mother and baby.
  • Genetic issues.

What the literature tells us

  • Although any one risk factor, if severe, may be sufficient to cause CP, more often it is the presence of multiple risk factors that leads to CP. One factor may interact with another to cause the brain injury, such as an event (or events) during pregnancy combined with the stress of birth combined with a genetic vulnerability.
  • The literature suggests that events during pregnancy are more likely to cause CP than events during labor or delivery. More specifically: a) A major US study called the Collaborative Perinatal Project conducted between 1959 and 1974 followed approximately 50,000 women and their children from the first prenatal visit until the children were seven years old. It found that events during labor and delivery were not major contributors to the occurrence of CP; most cases had their origins before labor began. A second finding was that intrauterine inflammation was a major cause of adverse pregnancy outcome. b) At least 70 percent of cases of CP have antecedents during pregnancy, and only 10 to 20 percent of cases are related to the child’s birth. Neither the routine use of fetal monitoring during labor nor the increased incidence of caesarean births (factors which reduce risk during labor and delivery) have reduced the number of cases of CP. c) Most brain injuries which cause CP occur in the second half of pregnancy, a period when the rate of brain development is fastest.
  • Some risk factors are on the decline, but others are increasing. Advances in neonatal care have reduced the risk of birth injury. However, with these advances more preterm infants and infants with low birth weight are surviving, some of whom may develop CP. In vitro fertilization has led to more multiple births, and multiple births, as noted above, is a risk factor for CP. The fact that some risk factors are decreasing while others are increasing is leading to a change in the type of CP that develops. For example, an injury to a brain at 24 weeks can have a different effect than one at 28 weeks or 36 weeks. Until recently, babies born at 24 weeks would not have survived. Now, thankfully, many of these babies survive; however, some may develop CP. The most common types of CP differ in different parts of the world, depending on risk factors. 
  • In approximately 90 percent of cases, CP results from healthy brain tissue becoming damaged rather than from abnormalities in brain development.
  • Confirmation of the presence of a brain injury by magnetic resonance imaging (MRI) occurs in many but not all cases. Up to 17 percent of people with CP have normal MRI brain scans. Imaging may also help determine when the brain injury occurred.
  • The cause of CP in an individual child is very often unknown.

We don’t know what caused our son Tommy’s CP, but that is not unusual. Like many other parents, I would like to have known.

The above essay is from Spastic Diplegia–Bilateral Cerebral Palsy available here.

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