- Cerebral palsy occurs as a result of an intrapartum event in no more than 10% of cases.
- Only cerebral palsy involving spastic quadriplegia is associated with an acute interruption of the blood supply, while purely dyskinetic or ataxic cerebral palsy generally is genetic in origin.
- Epidemiologic studies have clearly demonstrated a causal relationship between premature birth and cerebral palsy.
Using findings from a 2003 task force, this article outlines current understanding of the causes of cerebral palsy, summarizes the updated criteria for determining whether it is the result of an intrapartum event, and assesses the association between cerebral palsy and various factors, including prematurity and multiple gestation.
Cerebral palsy is the most common developmental disability in the United States; roughly half a million Americans have some degree of the disorder. In a surveillance program initiated by the Centers for Disease Control and Prevention (CDC), the average annual prevalence rate was 2.8 per 1,000 children (ages 3 to 10, 1991-1994).2 Annually, at least 8,000 cases are diagnosed in infants, while almost 1,500 are identified in children of preschool age.3
How hypoxemia leads to brain damage
Although the spectrum of current thought on cerebral palsy’s etiology is beyond the scope of this article, the subject has been explored extensively in recent years.4 We now know that no more than 10% of cases are the result of an intrapartum event.
Brain damage does appear to be the end result of a hypoxemic event. This event follows significant—usually abrupt—reduction in either the umbilical or uterine blood flow. Animal models demonstrate that even 12 hours of hypoxemia in midtrimester are sufficient to cause neuronal death.5 During the third trimester, fetal hypoxemia of moderate severity—sometimes encountered in cases with placental insufficiency—also can cause brain damage. When hypoxemia occurs immediately before or during labor, it is called a “sentinel” event, usually involving such entities as premature placental separation, uterine rupture, acute maternal hypotension, prolapsed umbilical cord, ruptured vasa previa, and tightened true knot of the umbilical cord.
If the sentinel event is severe enough, the fetus dies in utero. Otherwise, a series of reactions occurs:
- Blood is redistributed to protect vital fetal organs such as the brain, heart, and adrenals. (This circulatory centralization is less feasible for preterm fetuses.)
- The hypoxia- and acidosis-induced vasodilatation in the brain is followed by hypoperfusion, a process that is facilitated by oxygen radicals.
- Finally, a reperfusion phase occurs, during which enzyme-mediated cellular damage is thought to result from a massive influx of calcium via damaged ion channels. At this phase, cellular injury is presumably caused by the inhibition of protein synthesis, the release of noxious agents, or by apoptosis. An intrauterine infection triggering the release of inflammatory agents may produce a similar effect.4
2003 task force redefines link between cerebral palsy and intrapartum event
It is seldom possible to determine the precise time brain damage occurs.5 This issue often arises during medicolegal proceedings, when the parties try to ascertain any cause-and-effect relationship between intrapartum events and cerebral palsy.6,7
To address this question, in 1999 the International Cerebral Palsy Task Force—composed of obstetricians, neonatologists, child neurologists, and other clinical and scientific specialists—developed a set of criteria that defined when such a causal relationship existed.5 These criteria were updated earlier this year by the American College of Obstetricians and Gynecologists (ACOG) Task Force on Neonatal Encephalopathy and Cerebral Palsy, in conjunction with the American Academy of Pediatrics.8 The task force concluded that:
- while neonatal encephalopathy does not always lead to permanent neurologic impairment, “the pathway from an intrapartum hypoxic-ischemic injury to subsequent cerebral palsy must progress through neonatal encephalopathy”;
- only cerebral palsy involving spastic quadriplegia is associated with an acute interruption of the blood supply;
- purely dyskinetic or ataxic cerebral palsy generally is genetic in origin; and
- most importantly, “approximately 70% of neonatal encephalopathy is secondary to events arising before the onset of labor.”8
It is seldom possible to determine the precise time brain damage occurs—an issue that often arises during medicolegal proceedings.