Fetal Alcohol Syndrome

There are several suggested diagnostic schemas for FAS (e.g., Bertrand et al., 2004 ; Chudley et al., 2005 ; Hoyme, 2005) and, while there are minor differences between them, all require anomalies in three distinct areas: (i) prenatal and postnatal growth deficits; (ii) facial dysmorphology; and (iii) central nervous system (CNS) dysfunction. Typically, growth retardation is defined as evidence of prenatal or postnatal weight or height at or below the 10th percentile, after correcting for age, gender, race, and other appropriate variables.

The Canadian guidelines also recommend evidence of a disproportionately low weight-to-height ratio at or below the 10th percentile. Most guidelines recommend three essential dysmorphic features – a smooth philtrum, a thin upper vermillion border, and small palpebral fissures – although the revised Institute of Medicine (IOM) guideline requires only two of the three characteristics (Hoyme et al., 2005). Finally, a diagnosis of FAS requires evidence of CNS abnormality. Within this criterion, the diagnostic schemas differ more substantially.

For example, the revised IOM guideline only requires evidence of structural brain abnormalities, such as diminished head circumference at or below the 10th percentile. The CDC criteria are more extensive, outlining structural, neurological, and functional CNS dysfunction. Structural anomalies may be evidenced by the two criteria delineated in the IOM guidelines, as well as brain abnormalities observed with neuroimaging techniques. Seizures or other signs of neurological damage not attributable to postnatal insult may qualify as evidence of neurological problems.

Lastly, functional abnormalities are defined as a global cognitive deficit (such as a decreased IQ), or deficits in three different functional CNS domains, which include cognition, behavior, executive functioning, and motor functioning. The Canadian guidelines outline eight domains that must be assessed: hard and soft neurologic signs; brain structure; cognition; communication; academic achievement; memory; executive functioning and abstract reasoning; and attention deficit/hyperactivity. Diagnosis requires evidence of impairment in three of these domains.

Alcohol crosses the placenta and rapidly reaches the fetus. Extensive studies have demonstrated equivalent fetal and maternal alcohol concentrations, suggesting an unimpeded bidirectional movement of alcohol between the 2 compartments. The fetus appears to depend on maternal hepatic detoxification because the activity of alcohol dehydrogenase (ADH) in the fetal liver is less than 10% of that observed in the adult liver. Furthermore, the amniotic fluid acts as a reservoir for alcohol, prolonging fetal exposure.

The mechanism for the spectrum of adverse effects on virtually all organ systems of the developing fetus is unknown. Ethanol and its metabolite acetaldehyde can alter fetal development by disrupting cellular differentiation and growth, disrupting DNA and protein synthesis and inhibiting cell migration. Both ethanol and acetaldehyde modify the intermediary metabolism of carbohydrates, proteins, and fats. Both also decrease the transfer of amino acids, glucose, folic acid, zinc, and other nutrients across the placental barrier, indirectly affecting fetal growth due to intrauterine nutrient deprivation. Elevated levels of erythropoietin in the cord blood of newborns exposed to alcohol are reported and suggest a state of chronic fetal hypoxia.