Critical Period - Fetal Alcohol Syndrome

Fetal Alcohol Syndrome

Animal studies of fetal development have indicated a critical period for the type of neuronal injury that causes fetal alcohol syndrome. In mice, for example, alcohol exposure around the 7th day of gestation can cause facial abnormalities associated with FAS (Coles 1994). Analogous results have been found in monkeys, and the general trend is that early exposure is much more deleterious on normal development than exposure later in gestation, even if a larger amount of alcohol is consumed in the later stages of pregnancy. Alcohol exposure later in pregnancy has its own set of results. In rats, alcohol exposure in the second half of gestation results in low brain weight because this is when neurons in the cortex differentiate and move to their appropriate functional areas. The presence of alcohol disturbs both the timing and cell migration process. In the rat equivalent of the “third trimester,” alcohol exposure causes malformation of the cerebellum and hippocampus. Human studies have also shown that alcohol exposure during the first trimester is correlated with craniofacial abnormalities and low birth weight. Cranial and facial abnormalities are most likely associated with alcohol exposure during the first 8 weeks of the first trimester, because normal facial dysmorphia is interrupted. Moreover, more severe anomalies have been linked with lower IQ.