Fetal Alcohol Syndrome (FAS) is the most severe manifestation within Fetal Alcohol Spectrum Disorders (FASD). This condition results from alcohol exposure during pregnancy, which permanently damages the developing fetus. A diagnosis of FAS requires a comprehensive, multidisciplinary clinical assessment confirming a specific pattern of abnormalities across four distinct domains. Meeting all four standardized medical criteria is necessary to ensure an accurate diagnosis and that the affected individual receives appropriate lifelong support.
Criterion 1: Confirmed Prenatal Alcohol Exposure
The diagnostic process begins by establishing that the developing fetus was exposed to alcohol during pregnancy, as this is the direct cause of the condition. While confirmed exposure is a prerequisite for other FASD diagnoses, a full FAS diagnosis can sometimes be made even if the exposure history is unknown, provided the other three criteria are fully met. Clinicians seek documentation or reliable reports from the mother, medical records, or collateral sources to confirm the quantity, frequency, and timing of alcohol use. Heavy, frequent consumption, especially binge drinking (defined as four or more drinks per occasion), is particularly detrimental because it leads to high peak blood alcohol concentrations that overwhelm the fetal system. Documenting exposure is often challenging, but the goal is to determine if the level was sufficient to cause the observed pattern of birth defects and neurodevelopmental issues.
Criterion 2: Characteristic Facial Features
The second criterion focuses on three distinct physical features that constitute minor facial anomalies specific to FAS. These features arise because facial structures are highly sensitive to the toxic effects of alcohol during early development. All three cardinal features must be present for an FAS diagnosis and are objectively measured by a trained dysmorphologist.
One required feature is short palpebral fissures, referring to the small horizontal width of the eye opening, typically falling at or below the 10th percentile for age. The second feature is a smooth philtrum, the vertical groove located between the base of the nose and the upper lip. In affected individuals, this groove is flattened and scored clinically using a standardized scale to confirm the severity of the smoothness.
The third characteristic feature is a thin vermilion border, describing a noticeably thin upper lip. Like the philtrum, the thinness of the upper lip is objectively assessed using a standardized lip/philtrum guide. Scores of four or five on a five-point scale confirm the presence of this physical marker. These three features—short palpebral fissures, smooth philtrum, and thin upper lip—must coexist to fulfill the facial features criterion. Their presence at any point in the lifespan is sufficient for diagnosis when all other criteria are met.
Criterion 3: Growth Deficits
The third criterion involves documenting significant growth deficiency, observable before birth, after birth, or both. This deficit results directly from alcohol interfering with cell growth and proliferation throughout the body. The standard metric is a measurement of height or weight, or both, that falls at or below the 10th percentile when plotted on a standardized growth chart for the child’s age and sex.
The assessment must account for any other factors that could contribute to poor growth, such as poor postnatal nutrition or other medical conditions, to ensure the deficit is specifically attributable to the prenatal alcohol exposure. Clinicians must plot the measurements against appropriate growth curves, sometimes adjusting for race, ethnicity, or gestational age in premature infants, to ensure the growth deficiency is accurately quantified. This physical manifestation of reduced growth reflects the systemic impact of alcohol exposure on the body’s ability to develop normally.
Criterion 4: Central Nervous System Impairment
The final and most functionally significant criterion requires documented evidence of damage to the central nervous system (CNS), encompassing both structural abnormalities and functional neurodevelopmental impairment. Structural abnormalities involve physical damage to the brain, detected through medical imaging or by measuring a small head circumference. Microcephaly, defined as a head circumference at or below the 10th percentile, is a common finding suggesting deficient brain growth. More specific structural anomalies, such as abnormalities of the corpus callosum or cerebellar hypoplasia, can be identified via magnetic resonance imaging (MRI).
Beyond structural changes, the criterion requires evidence of significant functional impairment that cannot be explained by other factors. This impairment must be demonstrated through standardized testing, revealing significant deficits in at least three distinct neurodevelopmental domains. Affected functional domains include cognitive and intellectual function, such as a low IQ score, or specific learning deficits.
Executive function is a frequently affected domain, encompassing difficulties with planning, organization, impulse control, and working memory. Impairments in attention, memory, motor skills, or social and adaptive functioning can also contribute to meeting this criterion. A deficit is considered clinically significant when a child scores at least 1.5 to 2 standard deviations below the mean for their age in the required number of domains.
Affected Functional Domains
Affected domains include:
- Cognitive and intellectual function (e.g., low IQ score or specific learning deficits).
- Executive function.
- Attention.
- Memory.
- Motor skills.
- Social and adaptive functioning.
This widespread functional impairment dictates the long-term needs of the individual. It highlights the lasting impact of prenatal alcohol exposure on the brain.