been brought to expression at this early stage. Up to term, fetal tissues do not have significant capacity for the detoxification of ethanol, and the fetus remains exposed to ethanol in the amniotic fluid for periods far longer than the decay time of ethanol in the maternal circulation. The lack of significant quantities of ADH and ALDH means that fetal tissues have much lower quantities of antioxidant enzymes, like SOD, glutathione transferases, and glutathion peroxidases, resulting in antioxidant protection being much less effective. Additionally, ethanol may alter fetal development by interfering with retinoic acid signaling. Acetaldehyde, the main ethanol metabolite, can compete with retinaldehyde and prevent its oxidation to retinoic acid. Diagnosis Because admission of alcohol use during pregnancy can stigmatize birth mothers, many are reluctant to admit to drinking or to provide an accurate report of the quantity they drank. This complicates diagnosis and treatment of the syndrome. As a result, diagnosis of the severity of FASD relies on protocols of observation of the child's physiology and behavior rather than maternal self-reporting. Presently, four FASD diagnostic systems that diagnose FAS and other FASD conditions have been developed in North America: The Institute of Medicine's guidelines for FAS, the first system to standardize diagnoses of individuals with prenatal alcohol exposure; The University of Washington's "The 4-Digit Diagnostic Code", which ranks the four key features of FASD on a Likert scale of one to four and yields 256 descriptive codes that can be categorized into 22 distinct clinical categories, ranging from FAS to no findings; The Centers for Disease Control's "Fetal Alcohol Syndrome: Guidelines for Referral and Diagnosis", which established consensus on the diagnosis FAS in the U.S. but deferred addressing other FASD conditions; and Canadian guidelines for FASD diagnoses, which established criteria for diagnosing FASD in Canada and harmonized most differences between the IOM and University of Washington's systems. Each diagnostic system requires that a complete FASD evaluation includes an assessment of the four key features of FASD, described below. A positive finding on all four features is required for a diagnosis of FAS. However, prenatal alcohol exposure and central nervous system damage are the critical elements of the spectrum of FASD, and a positive finding in these two features is sufficient for an FASD diagnosis that is not "full-blown FAS". While the four diagnostic systems essentially agree on criteria for fetal alcohol syndrome (FAS), there are still differences when