the changed habits of light drinkers. Women who drink heavily, who pose the greatest risk to their fetus, appear to be more resistant to prevention efforts. Heavy drinking and the consequent incidence of fetal alcohol syndrome are much higher among black Americans than among white Americans (Abel, 1995; Faden et al., 1997) and are also high among American Indians (Duimstra et al., 1993).

Fetal alcohol syndrome is the most severe form of prenatal alcohol effects. Defined by a specific pattern of facial and other physical deformities accompanied by growth retardation, fetal alcohol syndrome identifies a relatively small proportion of children prenatally affected by alcohol. The Institute of Medicine (1996) recently suggested that the term “alcohol-related neurodevelopmental disorder” be used to focus specifically on brain dysfunctions in the presence of significant prenatal alcohol exposure but without physical deformities. Fetal alcohol syndrome is estimated to occur at a rate of 1-3 per 1,000 live births; alcohol-related neurodevelopmental disorder is estimated to be at least 10 times more prevalent. Brain dysfunctions in alcohol-exposed children without fetal alcohol syndrome are often as severe as those in children with the full impairment.

A variety of neurobehavioral changes have been observed in children exposed to alcohol prenatally. These effects range from problems with attention and memory to poor motor coordination to difficulty with problem solving and abstract thinking. Infants and toddlers may be delayed in reaching important milestones, may have difficulty tuning out excess sensory stimuli, and often are hyperactive. About half of all individuals with fetal alcohol syndrome are mentally retarded (IQ < 70). Both severely and more mildly affected children demonstrate slower information processing and longer reaction times and appear to have specific problems with arithmetic (Jacobson et al., 1994). These effects have been documented through the early adolescent years and into adulthood. Such results demonstrate the importance of assessing functions other than IQ. In fact, these measures often detect effects of early biological insults in the absence of IQ differences, and behavioral disturbances may create more functional impairment than a lower IQ. In addition, more specific and sensitive measures may indicate differing effects of various developmental neurotoxins (Jacobson, 1998).

The importance of considering timing (when a condition occurs during development), severity (degree or dose), and chronicity (how long it lasts) in attempting to understand the effects of early biological insults is well illustrated by prenatal alcohol exposure. In general, the prenatal period appears to be distinguished by its sensitivity to a large array of harmful conditions. But even within the prenatal period, timing matters. For instance, alcohol exposure early in gestation has different effects on the developing brain from similar exposure later on. Case reports from autop-



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