[This post is part of our Knowledge Translation/Education Tuesday series. Guest author Lily Collison, author of Spastic Diplegia–Bilateral Cerebral Palsy, continues the series.]

Our home is in Sligo, on the north west coast of Ireland. It’s known for its scenery and also its association with the poet, WB Yeats. Sligo has special mountains–Knocknarea (really only a hill, included in a previous post) and Ben Bulben above (elevation 1,726 feet).

In my last post I gave a typical list of causes of and risk factors for CP. This week I will look at some studies that give us further insight.

• 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 vulnerability¹.
• The literature suggests that events during pregnancy are more likely to cause CP than events during labor or delivery. More specifically:
• 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 outcome².
• 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 birth³. 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 CP³.
• Most brain injuries which cause CP occur in the second half of pregnancy, a period when the rate of brain development is fastest⁴.
• Some risk factors are on the decline, but others are increasing^3,5. 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 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 development⁵.
• 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 scans⁵. Imaging may also help determine when the brain injury occurred⁵.
• The cause of CP in an individual child is very often unknown⁶.

Though I did not know what caused Tommy’s CP, in the early days I wasted a lot of time feeling guilty. I had worked very hard and was stressed during his pregnancy, and I felt responsible. Today I no longer feel that sense of guilt. I didn’t knowingly do anything wrong: my life circumstances were such that I was very busy, and besides, there are multiple possible causes of brain injury. I encourage parents to waste no time on guilt—we are where we are and we must move forward.

* Things that existed before or that logically preceded another event.

¹Nelson KB (2008) Causative factors in cerebral palsy. Clin Obstet Gynecol 51: 749–762.
²Klebanoff MA (2009) The collaborative perinatal project: a 50-year prospective. Pediatr Perinat Epidemiol 23: 2–8.
³Graham HK, Thomason P, Novacheck TF (2014) Cerebral palsy. In: Weinstein SL, Flynn JM, editors, Lovell and Winter’s Pediatric Orthopedics, Level 1 and 2. Philadelphia: Lippincott Williams & Wilkins, pp 484–554.
⁴Hadders-Algra M (2014) Early diagnosis and early intervention in cerebral palsy. Front Neurol 5(185): 1–13.
⁵Graham HK, Rosenbaum P, Paneth N, et al. (2016) Cerebral palsy. Nat Rev Dis Primers 2: 1–24.
⁶Rosenbaum P, Rosenbloom L (2012) Cerebral Palsy: From Diagnosis to Adulthood. London: Mac Keith Press.