Fetal alcohol spectrum disorder
Fetal Alcohol Spectrum Disorders (FASD) describes a continuum of permanent birth defects caused by maternal consumption of alcohol during pregnancy, which includes, but is not limited to Fetal alcohol syndrome (FAS).
Over time, as it became apparent through research and clinical experience that a range of effects (including physical, behavioral, and cognitive) could arise from prenatal alcohol exposure, the term Fetal Alcohol Spectrum Disorders, or FASD, was developed to include Fetal alcohol syndrome (FAS) as well as other conditions resulting from prenatal alcohol exposure.  There are a number of other subtypes with evolving nomenclature and definitions based on partial expressions of FAS, including Partial Fetal Alcohol Syndrome (PFAS), Alcohol-Related Neurodevelopmental Disorder (ARND), Alcohol-Related Birth Defects (ARBD), and Fetal Alcohol Effect (FAE).
The term Fetal Alcohol Spectrum Disorders is not in itself a clinical diagnosis but describes the full range of disabilities that may result from prenatal alcohol exposure. Currently, Fetal Alcohol Syndrome (FAS) is the only expression of prenatal alcohol exposure that is defined by the International Statistical Classification of Diseases and Related Health Problems and assigned ICD-9 and ICD-10 diagnoses.

# Diagnostic systems
Since the original syndrome of Fetal Alcohol Syndrome (FAS) was reported in 1973, four FASD diagnostic systems that diagnose FAS and other FASD conditions 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,
- The University 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 diagnoses, which established criteria for diagnosing FASD in Canada and harmonized most differences between the IOM and University of Washington's systems.
Each diagnostic system requires that a complete FASD evaluation include assessment of the four key features of FASD, described below. A positive finding on all four features is required for a diagnosis of FAS, the first diagnosable condition of FASD that was discovered. However, prenatal alcohol exposure and central nervous system damage are the critical elements of the spectrum of FASD, and a positive finding in these two features is sufficient for an FASD diagnosis that is not "full-blown FAS." Diagnoses are described in a following section.

# Key features of FASD
Each of the key features of FASD can vary widely within one individual exposed to prenatal alcohol. While consensus exists for the definition and diagnosis of FAS across diagnostic systems, minor variations among the systems lead to differences in definitions and diagnostic cut-off criteria for other disgnoses across the FASD continuum. (The central nervous system (CNS) damage criteria particularly lack clear consensus.) A working knowledge of the key features is helpful in understanding FASD diagnoses and conditions, and each are reviewed with attention to similarities and differences across the four diagnostic systems.

## Growth deficiency
In terms of FASD, growth deficiency is defined as significantly below average height, weight or both due to prenatal alcohol exposure, and can be assessed at any point in the lifespan. Growth measurements must be adjusted for parental height, gestational age (for a premature infant), and other postnatal insults (e.g., poor nutrition), although birth height and weight are the preferred measurements. Deficiencies are documented when height or weight falls at or below the 10th percentile of standardized growth charts appropriate to the patient's population.
Criteria for FASD are least specific in the IOM diagnostic system ("low birth weight..., decelerating weight not due to nutrition...,  disproportional low weight to height" p.4 of executive summary), while the CDC and Canadian guidelines use the 10th percentile as a cut-off to determine growth deficiency. The "4-Digit Diagnostic Code" allows for mid-range gradations in growth deficiency (between the 3rd and 10th percentiles) and severe growth deficiency at or below the 3rd percentile. Growth deficiency (at severe, moderate, or mild levels) contributes to diagnoses of FAS and PFAS, but not ARND or static encephalopathy.
Growth deficiency is ranked as follows by the "4-Digit Diagnostic Code:"
- Severe - Height and weight at or below the 3rd percentile.
- 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 patients 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 original study that determined the definition of FAS. This reinforces assertions that growth deficiency and FAS facial features are less critical for understanding the disability of FASD than the neurobehavioral sequelae to the brain damage.

## FAS facial features
Several characteristic craniofacial abnormalities are visible in individuals with FAS, but these may be mild or even non-existent in other FASD conditions.
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.
- Small palpebral fissures - Eye width shortens with increased prenatal alcohol exposure.
Measurement of FAS facial features uses criteria developed by the University of Washington. The lip and philtrum are measured by a trained physician with the Lip-Philtrum Guide,  a 5-point Likert Scale with representative photographs of lip and philtrum combinations ranging from normal (ranked 1) to severe (ranked 5). Palpebral fissure length (PFL) is measured in millimeters with either calipers or a clear ruler and then compared to a PFL growth chart, also developed by the University of Washington.
All four diagnostic systems have agreed upon this method for determining FAS facial feature severity rankings.  Ranking FAS facial features is complicated because the three separate facial features can be affected independently by prenatal alcohol.

## Central nervous system damage
Central nervous system (CNS) damage is the primary key feature of any FASD diagnosis. Prenatal alcohol exposure, 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 diagnoses 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.
- Unlikely - No evidence of CNS damage.

### Structural
Structural abnormalities of the brain are observable, physical damage to the brain or brain structures caused by prenatal alcohol exposure. Structural impairments may include microcephaly (small head size) of two or more standard deviations below the average, or other abnormalities in brain structure (e.g., agenesis of the corpus callosum, cerebellar hypoplasia).
Microcephaly is determined by comparing head circumference (often called occipitofrontal circumference, or OFC) to appropriate OFC growth charts. Other structural impairments must be observed through medical imaging techniques by a trained physician. Because imaging procedures are expensive and relatively inaccessible to most patients, diagnosis of FASD is not frequently made via structural impairments except for microcephaly.

### Neurological
When structural impairments are not observable or do not exist, neurological impairments are assessed. In the context of FASD, neurological impairments are caused by prenatal alcohol exposure which causes general neurological damage to the central nervous system (CNS), the peripheral nervous system, or the autonomic nervous system. A determination of a neurological problem must be made by a trained physician, and must not be due to a postnatal insult, such as a high fever, concussion, traumatic brain injury, etc.
All four diagnostic systems show virtual agreement on their criteria for CNS damage at the neurological level, and evidence of a CNS neurological impairment due to prenatal alcohol exposure will result in a diagnosis of FAS or PFAS, and functional impairments are highly likely.
Neurological problems are expressed as either hard signs, or diagnosable disorders, such as epilepsy or other seizure disorders, or soft signs. Soft signs are broader, nonspecific neurological impairments, or symptoms, such as impaired fine motor skills, neurosensory hearing loss, poor gait, clumsiness, poor eye-hand coordination, or sensory integration dysfunction. Many soft signs have norm-referenced criteria, while others are determined through clinical judgment.

### Functional
When structural or neurological impairments are not observed, all four diagnostic systems allow CNS damage due to prenatal alcohol exposure to be assessed in terms of functional impairments. Functional impairments are deficits, problems, delays, or abnormalities due to prenatal alcohol exposure (rather than hereditary causes or postnatal insults) in observable and measurable domains related to daily functioning, often referred to as developmental disabilities. There is no consensus on a specific pattern of functional impairments due to prenatal alcohol exposure and only CDC guidelines label developmental delays as such, so criteria (and FASD diagnoses) vary somewhat across diagnostic systems.
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 guidelines
Learning disabilities, academic achievement, impulse control, social perception, communication, abstraction, math skills, memory, attention, judgment
- Learning 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 Code
Executive functioning, memory, cognition, social/adaptive skills, academic achievement, language, motor skills, attention, activity level
- Executive 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 guidelines
Cognition, executive functioning, motor functioning, attention and hyperactive problems, social skills, sensory problems, social communication, memory, difficulties responding to common parenting practices
- Cognition, executive functioning, motor functioning, attention and hyperactive problems, social skills, sensory problems, 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, social skills, social communication
- Cognition, communication, academic achievement, memory, executive functioning, adaptive behavior, social skills, social communication
A recent effort to standardize assessment of functional CNS damage has been suggested by an experienced FASD diagnostic team in Minnesota. The proposed framework attempts to harmonize IOM, 4-Digit Diagnostic Code, CDC, and Canadian guidelines for measuring CNS damage viz-a-viz FASD evaluations and diagnosis. The standardized approach is referred to as the Ten Brain Domains and encompasses aspects of all four diagnostic systems' recommendations for assessing CNS damage due to prenatal alcohol exposure. The framework provides clear definitions of brain dysfunction, specifies empirical data needed for accurate diagnosis, and defines intervention considerations that address the complex nature of FASD with the intention to avoid common secondary disabilities.
The proposed Ten Brain Domains include:
- Achievement, adaptive behavior, attention, cognition, executive functioning, language, memory, motor skills, sensory integration or soft neurological problems, social communication
The Fetal Alcohol Diagnostic Program (FADP) uses unpublished Minnesota state criteria of performance at 1.5 or more standard deviations on standardized testing in three or more of the Ten Brain Domains to determine CNS damage. However, the Ten Brain Domains are easily incorporated into any of the four diagnostic systems' CNS damage criteria, as the framework only proposes the domains, rather than the cut-off criteria for FASD.

## Prenatal alcohol exposure
Prenatal alcohol exposure is determined by interview of the biological mother or other family members knowledgeable of the mother's alcohol use during the pregnancy (if available), prenatal health records (if available), and review of available birth records, court records (if applicable), chemical dependency treatment records (if applicable), 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 (100mg/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.

### Confirmed exposure
Amount, frequency, and timing of prenatal alcohol use can dramatically impact the other three key features of FASD. 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 100mg/dL delivered at least weekly in early pregnancy. This BAC level is typically reached by a 55kg female 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. 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.

### Confirmed absence of exposure
Confirmed absence of exposure would apply to planned pregnancies in which no alcohol was used or pregnancies of women who do not use alcohol or report no use during the pregnancy. This designation is relatively rare, as most patients presenting for an FASD evaluation are at least suspected to have had a prenatal alcohol exposure due to presence of other key features of FASD.

# Diagnosis
While the four diagnostic systems essentially agree on criteria for Fetal Alcohol Syndrome (FAS), there are still differences when full criteria for FAS are not met. This has resulted in differing and evolving nomenclature for other conditions across the spectrum of FASD, which may account for such a wide variety of terminology. Most individuals with deficits resulting from prenatal alcohol exposure do not express all features of FAS and fall into other FASD conditions. The Canadian guidelines recommend the assessment and descriptive approach of the "4-Digit Diagnostic Code" for each key feature of FASD and the terminology of the IOM in diagnostic categories, excepting ARBD.
Fetal Alcohol Syndrome or FAS 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, speech-language, and occupational therapy assessments to ascertain clinically significant impairments in three or more of the Ten Brain Domains. Prenatal alcohol exposure risk may be assessed by a qualified physician, psychologist, social worker, or chemical health counselor. These professionals work together as a team to assess and interpret data of each key feature for assessment and develop an integrative, multi-disciplinary report to diagnose FAS (or other FASD conditions) in an individual.

## Other FASD diagnoses
Other FASD conditions are partial expressions of FAS, and here the terminology shows less consensus across diagnostic systems, which has led to some confusion for clinicians and patients. A key point to remember is that other FASD conditions may create disabilities similar to FAS if the key area of central nervous system damage shows clinical deficits in two or more of the Ten Brain Domains. Essentially, growth deficiency and/or FAS facial features may be mild or nonexistent in other FASD conditions, but clinically significant brain damage of the central nervous system is present. In these other FASD conditions, an individual may be at greater risk for adverse outcomes because brain damage is present without associated visual cues of poor growth or the "FAS face" that might ordinarily trigger an FASD evaluation. Such individuals may be misdiagnosed with primary mental health disorders such as ADHD or Oppositional Defiance Disorder without appreciation that brain damage is the underlying cause of these disorders, which requires a different treatment paradigm than typical mental health disorders. While other FASD conditions may not yet be included as an ICD or DSM-IV-TR diagnosis, they nonetheless pose significant impairment in functional behavior because of underlying brain damage.

### Partial FAS (PFAS)
Previously known as Atypical FAS in the 1997 edition of the "4-Digit Diagnostic Code," patients with Partial Fetal Alcohol Syndrome have a confirmed history of prenatal alcohol exposure, but may lack growth deficiency or the complete facial stigmata. Central nervous system damage is present at the same level as FAS. These individuals have the same functional disabilities but "look" less like FAS.
The following criteria must be fully met for a diagnosis of Partial FAS:
- Growth deficiency - Growth or height may range from normal to deficient
- FAS facial features - Two or three FAS facial features present
- Central nervous system damage - Clinically significant structural, neurological, or functional impairment in three or more of the Ten Brain Domains
- Prenatal alcohol exposure - Confirmed prenatal alcohol exposure

### Alcohol-Related Neurodevelopmental Disorder (ARND)
Alcohol-Related Neurodevelopmental Disorder (ARND) was initially suggested by the Institute of Medicine to replace the term FAE and focus on central nervous system damage, rather than growth deficiency or FAS facial features. The Canadian guidelines also use this diagnosis and the same criteria. While the "4-Digit Diagnostic Code" includes these criteria for three of its diagnostic categories, it refers to this condition as static encephalopathy. The behavioral effects of ARND are not necessarily unique to alcohol however, so use of the term must be within the context of confirmed prenatal alcohol exposure. ARND may be gaining acceptance over the terms FAE and ARBD to describe FASD conditions with central nervous system abnormalities or behavioral or cognitive abnormalities or both due to prenatal alcohol exposure without regard to growth deficiency or FAS facial features.
The following criteria must be fully met for a diagnosis of ARND or static encephalopathy:
- Growth deficiency - Growth or height may range from normal to minimally deficient
- FAS facial features - Minimal or no FAS facial features present
- Central nervous system damage - Clinically significant structural, neurological, or functional impairment in three or more of the Ten Brain Domains
- Prenatal alcohol exposure - Confirmed prenatal alcohol exposure

### Fetal Alcohol Effects (FAE)
This term was initially used in research studies to describe humans and animals in whom teratogenic effects were seen after confirmed prenatal alcohol exposure (or unknown exposure for humans), but without obvious physical anomalies. Smith (1981) described FAE as an "extremely important concept" to highlight the debilitating effects of brain damage, regardless of the growth or facial features. This term has fallen out of favor with clinicians because it was often regarded by the public as a less severe disability than FAS, when in fact its effects can be just as detrimental.

### Alcohol-Related Birth Defects (ARBD)
Formerly known as Possible Fetal Alcohol Effect (PFAE), Alcohol-Related Birth Defects (ARBD) was a term proposed as an alternative to FAE and PFAE The IOM presents ARBD as a list of congenital anomalies that are linked to maternal alcohol use but have no key features of FASD. PFAE and ARBD have fallen out of favor because these anomalies are not necessarily specific to maternal alcohol consumption and are not criteria for diagnosis of FASD. The Canadian guidelines recommend that ARBD should not be used as an umbrella term or diagnostic category for FASD.