Unlikely: No evidence of CNS damage. Structural
Structural abnormalities of the brain are observable, physical damage to the brain or brain structures caused by prenatal alcohol exposure. Structural impairments may include microcephaly (small head size) of two or more standard deviations below the average, or other abnormalities in brain structure (e.g., agenesis of the corpus callosum, cerebellar hypoplasia).Microcephaly is determined by comparing head circumference (often called occipitofrontal circumference, or OFC) to appropriate OFC growth charts. Other structural impairments must be observed through medical imaging techniques by a trained physician. Because imaging procedures are expensive and relatively inaccessible to most people, diagnosis of FAS is not frequently made via structural impairments, except for microcephaly.Evidence of a CNS structural impairment due to prenatal alcohol exposure will result in a diagnosis of FAS, and neurological and functional impairments are highly likely.During the first trimester of pregnancy, alcohol interferes with the migration and organization of brain cells, which can create structural deformities or deficits within the brain. During the third trimester, damage can be caused to the hippocampus, which plays a role in memory, learning, emotion, and encoding visual and auditory information, all of which can create neurological and functional CNS impairments as well.As of 2002, there were 25 reports of autopsies on infants known to have FAS. The first was in 1973, on an infant who died shortly after birth.
Exposure
Prenatal alcohol exposure is determined by interview of the biological mother or other family members knowledgeable of the mothers alcohol use during the pregnancy (if available), prenatal health records (if available), and review of available birth records, court records (if applicable), chemical dependency treatment records (if applicable), chemical biomarkers, or other reliable sources. Exposure level is assessed as confirmed exposure, unknown exposure, and confirmed absence of exposure by the IOM, CDC and Canadian diagnostic systems. The "4-Digit Diagnostic Code" further distinguishes confirmed exposure as High Risk and Some Risk:
High Risk: Confirmed use of alcohol during pregnancy known to be at high blood alcohol levels (100 mg/dL or greater) delivered at least weekly in early pregnancy. Some Risk: Confirmed use of alcohol during pregnancy with use less than High Risk or unknown usage patterns. Unknown Risk: Unknown use of alcohol during pregnancy. No Risk: Confirmed absence of prenatal alcohol exposure. Confirmed exposure
Amount, frequency, and timing of prenatal alcohol use can dramatically impact the other three key features of FASD. While consensus exists that alcohol is a teratogen, there is no clear consensus as to what level of exposure is toxic. The CDC guidelines are silent on these elements diagnostically. The IOM and Canadian guidelines explore this further, acknowledging the importance of significant alcohol exposure from regular or heavy episodic alcohol consumption in determining, but offer no standard for diagnosis.