The four diagnostic systems list various CNS domains that can qualify for functional impairment that can determine an FASD diagnosis:

Evidence of a complex pattern of behavior or cognitive abnormalities inconsistent with developmental level in the following CNS domains – Sufficient for a pFAS or ARND diagnosis using IOM guidelinesLearning disabilities, academic achievement, impulse control, social perception, communication, abstraction, math skills, memory, attention, judgment
Performance at two or more standard deviations on standardized testing in three or more of the following CNS domains – Sufficient for an FAS, pFAS or static encephalopathy diagnosis using 4-Digit Diagnostic CodeExecutive functioning, memory, cognition, social/adaptive skills, academic achievement, language, motor skills, attention, activity level
General cognitive deficits (e.g., IQ) at or below the 3rd percentile on standardized testing – Sufficient for an FAS diagnosis using CDC guidelines
Performance at or below the 16th percentile on standardized testing in three or more of the following CNS domains – Sufficient for an FAS diagnosis using CDC guidelinesCognition, executive functioning, motor functioning, attention and hyperactive problems, social skills, sensory processing disorder, social communication, memory, difficulties responding to common parenting practices
Performance at two or more standard deviations on standardized testing in three or more of the following CNS domains – Sufficient for an FAS diagnosis using Canadian guidelines
Cognition, communication, academic achievement, memory, executive functioning, adaptive behavior, motor skills, social skills, social communication

Related signs
Other conditions may commonly co-occur with FAS, stemming from prenatal alcohol exposure. However, these conditions are considered alcohol-related birth defects and not diagnostic criteria for FAS.
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.