Moderate: Either height or weight at or below the 3rd percentile, but not both. Mild: Either height or weight or both between the 3rd and 10th percentiles. None: Height and weight both above the 10th percentile.In the initial studies that discovered FAS, growth deficiency was a requirement for inclusion in the studies; thus, all the original people with FAS had growth deficiency as an artifact of sampling characteristics used to establish criteria for the syndrome. That is, growth deficiency is a key feature of FASD because growth deficiency was a criterion for inclusion in the study that defined FAS. This suggests growth deficiency may be less critical for understanding the disabilities of FASD than the neurobehavioral sequelae to the brain damage. Facial features
Several characteristic craniofacial abnormalities are often visible in individuals with FAS. The presence of FAS facial features indicates brain damage, although brain damage may also exist in their absence. FAS facial features (and most other visible, but non-diagnostic, deformities) are believed to be caused mainly during the 10th to 20th week of gestation.Refinements in diagnostic criteria since 1975 have yielded three distinctive and diagnostically significant facial features known to result from prenatal alcohol exposure and distinguishes FAS from other disorders with partially overlapping characteristics. The three FAS facial features are:

A smooth philtrum: The divot or groove between the nose and upper lip flattens with increased prenatal alcohol exposure. Thin vermilion: The upper lip thins with increased prenatal alcohol exposure.
Prenatal alcohol exposure, which is classified as a teratogen, can damage the brain across a continuum of gross to subtle impairments, depending on the amount, timing, and frequency of the exposure as well as genetic predispositions of the fetus and mother. While functional abnormalities are the behavioral and cognitive expressions of the FASD disability, CNS damage can be assessed in three areas: structural, neurological, and functional impairments.All four diagnostic systems allow for assessment of CNS damage in these areas, but criteria vary. The IOM system requires structural or neurological impairment for a diagnosis of FAS, but also allows a "complex pattern" of functional anomalies for diagnosing PFAS and ARND. The "4-Digit Diagnostic Code" and CDC guidelines allow for a positive CNS finding in any of the three areas for any FASD diagnosis, but functional anomalies must measure at two standard deviations or worse in three or more functional domains for a diagnosis of FAS, PFAS, and ARND. The "4-Digit Diagnostic Code" also allows for an FASD diagnosis when only two functional domains are measured at two standard deviations or worse. The "4-Digit Diagnostic Code" further elaborates the degree of CNS damage according to four ranks:

Definite: Structural impairments or neurological impairments for FAS or static encephalopathy. Probable: Significant dysfunction of two standard deviations or worse in three or more functional domains. Possible: Mild to moderate dysfunction of two standard deviations or worse in one or two functional domains or by judgment of the clinical evaluation team that CNS damage cannot be dismissed.