Cerebral palsy (CP) is a general term to describe a group of chronic conditions that impair control of movement and posture. CP is due to malformation of or damage to motor areas in the brain, which disrupts the brain’s ability to control movement and posture. Symptoms of CP may range from mild to severe, change over time and differ from person to person, and include difficulty with balance, walking, and fine motor tasks (such as writing or using scissors) and involuntary movements. Many people with CP also have associated cognitive, sensory, social, and emotional disabilities (NIDS, 2005).
The diagnosis of CP may not become certain until the second year of life. As many as 17 to 48 percent of preterm infants demonstrate neuromotor abnormalities during infancy (e.g., abnormal muscle tone or asymmetries) (Allen and Capute, 1989; Khadilkar et al., 1993; Pallas Alonso et al., 2000; Vohr et al., 2005). Some of these infants go on to develop significant neuromotor abnormalities and motor delays that signify CP, but most do not. Although neuromotor abnormalities tend to resolve or do not interfere with function, transient neuromotor abnormalities are associated with an increased risk of later school and behavioral problems (Drillien et al., 1980; Khadilkar et al., 1993; Sommerfelt et al., 1996; Vohr et al., 2005).
The severity of CP is determined by the type of CP, which limbs are affected, and the degree of functional limitation. Increasingly, investigators are distinguishing between mild CP and moderate to severe (i.e., disabling) CP (Doyle and Anderson, 2005; Grether et al. 2000; Vohr et al., 2005; Wood et al., 2000). Many longitudinal studies of the outcomes for preterm infants show good stability between motor assessments at 18 to 30 months of age and at school age (Hack et al., 2002; Marlow et al., 2005; Wood et al., 2000).
The smallest and most immature infants have the highest risk of CP. In their seventh report of CP in Sweden, Hagberg and associates (1996) reported an almost stepwise increase in the prevalence of CP with gestational age: 1.4 per 1,000 live births for children born at more than 36 weeks gestation, 8 per 1,000 live births for children born between 32 and 36 weeks gestation, 54 per 1,000 live births for children born between 28 and 31 weeks gestation, and 80 per 1,000 live births for children born at less than 28 weeks of gestation. Because they report prevalence as the number who have CP per 1,000 live births, infants who die are included in the denominator.
For the most immature infants, another meaningful statistic is the rate of CP among survivors. On the basis of data for preterm survivors born in the late 1980s through the 1990s, the rate of CP increases with decreasing