Several diagnostic systems 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
TheUniversity 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 general consensus on the diagnosis FAS in the U.S. but deferred addressing other FASD conditions, and Canadian guidelines for FASD diagnosis, which established criteria for diagnosing FASD in Canada and harmonized most differences between the IOM and University of Washington's systems.
Fetal alcohol syndrome is the only expression of FASD that has garnered consensus among experts to become an official ICD-9 and ICD-10 diagnosis. To make this diagnosis (or determine any FASD condition), a multi-disciplinary evaluation is necessary to assess each of the four key features for assessment. Generally, a trained physician will determine growth deficiency and FAS facial features. While a qualified physician may also assess central nervous system structural abnormalities and/or neurological problems, usually central nervous system damage is determined through psychological assessment. A pediatric neuropsychologist may assess all areas of functioning, including intellectual, language processing, and sensorimotor. Prenatal alcohol exposure risk may be assessed by a qualified physician or psychologist.
The following criteria must be fully met for an FAS diagnosis:
Growth deficiency — Prenatal or postnatal height or weight (or both) at or below the 10th percentile
FAS facial features — All three FAS facial features present
Central nervous system damage — Clinically significant structural, neurological, or functional impairment
Prenatal alcohol exposure — Confirmed or Unknown prenatal alcohol exposure
Alcohol intake is determined by interview of the biological mother or other family members knowledgeable of the mother's alcohol use during the pregnancy, prenatal health records, and review of available birth records, court records, chemical dependency treatment records, 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, which rules out an FAS diagnosis.
Confirmed exposure
Amount, frequency, and timing of prenatal alcohol use can dramatically impact the other three key features of FAS. 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. Canadian guidelines discuss this lack of clarity and parenthetically point out that "heavy alcohol use" is defined by the National Institute on Alcohol Abuse and Alcoholism as five or more drinks per episode on five or more days during a 30 day period.
"The 4-Digit Diagnostic Code" ranking system distinguishes between levels of prenatal alcohol exposure as High Risk and Some Risk. It operationalizes high risk exposure as a blood alcohol concentration (BAC) greater than 100 mg/dL delivered at least weekly in early pregnancy. This BAC level is typically reached by a 55 kg woman drinking six to eight beers in one sitting.
Unknown exposure
For many adopted or adult patients and children in foster care, records or other reliable sources may not be available for review. Reporting alcohol use during pregnancy can also be stigmatizing to birth mothers, especially if alcohol use is ongoing.[18] In these cases, all diagnostic systems use an unknown prenatal alcohol exposure designation. A diagnosis of FAS is still possible with an unknown exposure level if other key features of FASD are present at clinical levels.
Differential diagnosis
The CDC reviewed nine syndromes that have overlapping features with FAS; however, none of these syndromes include all three FAS facial features, and none are the result of prenatal alcohol exposure:
Aarskog syndrome
Williams syndrome
Noonan syndrome
Dubowitz syndrome
Brachman-DeLange syndrome
Toluene syndrome
Fetal hydantoin syndrome
Fetal valproate syndrome
Maternal PKU fetal effects