Critical Periods for Prenatal Alcohol Exposure Evidence From Animal and Human Studies

A in 1968, Lemoine and drinking during pregnancy; the duration was considered the risky period—when colleagues (1968) informed the of the fetus’ exposure; and whether, if exposure might lead to birth defects— scientific and medical commu­ the fetus is exposed early in gestation, it whereas exposure during the later part of nity of alcohol’s potential as a makes any difference to the outcome if pregnancy was not considered dangerous. teratogen (i.e., alcohol is a substance that the mother discontinues her drinking for A possible explanation for this view can affect a developing fetus, resulting in the duration of her pregnancy. These involves the kinds of defects that generally physical and neurological damage), Jones questions concern the fetus’ vulnerability appear if exposure to a teratogen occurs and Smith’s (1973) classic article first during different critical periods of gesta­ early in pregnancy. The first trimester is employed the term “fetal alcohol syn­ tion. This article reviews research find­ the critical period of organogenesis, when drome” (FAS). It is evident from this and ings from studies of humans and animals the major organs form. Exposure during later reports that maternal alcoholism and about the effects of alcohol during critical this time, and particularly during the first 2 heavy drinking during pregnancy are periods in pregnancy. months—the embryonic period—can result associated with readily observable physi­ in dysmorphia. The effects of teratogenic cal defects, called dysmorphia; reduced exposure during the second and third growth; and damage to the fetus’ nervous CRITICAL PERIODS trimesters, which include growth retar­ system.1 However, the extent and pattern dation and neurological defects (Scialli of alcohol exposure necessary to produce In the first half of this century, the placenta 1992), are not as obvious and may not be any of these negative effects are still was considered a natural barrier capable of under investigation. Some of the most vexing questions protecting the developing child from expo­ CLAIRE COLES, PH.D., is director of Clini­ sure to harmful agents, including disease about alcohol’s effects on the fetus that cal and Developmental Research at the and toxic chemicals. When researchers remain concern the timing of a mother’s Human and Behavior Genetics Labora­ discovered, during the 1950’s and 1960’s, tory of the Department of Psychiatry and that certain diseases, such as rubella, and is director of Psychological Services at 1The terms “heavy drinking” and “alcoholism” do not some environmental agents, such as mer­ the Marcus Development Center of the refer to specific amounts of drinking or conditions. The amount of alcohol that must be consumed by a cury, were teratogenic (Scialli 1992), con­ Department of Pediatrics, the Emory pregnant woman in order to produce effects in her cern focused on the first 3 months of University School of Medicine, Atlanta, fetus has never been determined. pregnancy, the first trimester. This stage Georgia.