Fetal alcohol syndrome (FAS) is a condition caused by alcohol exposure in the womb. It produces a recognizable pattern of facial features, growth problems, and brain damage that lasts a lifetime. FAS is the most severe diagnosis within a broader range of conditions called fetal alcohol spectrum disorders (FASD), which includes related but less visible forms of alcohol-related harm to a developing baby.
How Alcohol Damages a Developing Baby
Alcohol crosses the placenta freely. When a pregnant person drinks, the fetus is exposed to the same blood alcohol concentration, but its immature liver processes it far more slowly. This makes alcohol a potent teratogen, a substance that disrupts normal development.
The damage is especially severe in the brain. During fetal development, blood vessels grow into the brain tissue in a carefully organized pattern, guided by specialized stem cells. Alcohol disrupts the signals that control this blood vessel growth, altering the density and organization of the brain’s vascular network. It also interferes with cell migration, the process by which newly formed brain cells travel to their correct positions. The result is structural brain abnormalities visible on imaging: a smaller or misshapen corpus callosum (the bridge connecting the brain’s two hemispheres), an underdeveloped cerebellum (which coordinates movement and balance), and changes in the basal ganglia (involved in learning and behavior). These structural problems are the root of the cognitive and behavioral difficulties that define FAS.
The Three Diagnostic Requirements
A diagnosis of FAS requires documentation of three findings: specific facial abnormalities, growth deficiency, and central nervous system abnormalities. All three must be present.
Facial Features
Three distinctive facial traits must all appear together:
- Short eye openings: the horizontal distance across each eye is significantly smaller than normal for age and ethnicity
- Smooth philtrum: the vertical groove between the nose and upper lip is flat or nearly absent, rather than having the typical ridged shape
- Thin upper lip: the red portion of the upper lip is unusually narrow
These features are measured using standardized guides that rank severity on a scale, with the most affected ranks (4 or 5 out of 5) required for diagnosis. The facial characteristics are most distinctive in early childhood and can become subtler with age, which is one reason early identification matters.
Growth Problems
Children with FAS are small. The diagnostic threshold is a height, weight, or both below the 10th percentile, adjusted for age, sex, gestational age, and ethnicity. Some diagnostic systems place greater emphasis on height deficiency over weight. Research from the University of Washington’s FAS Diagnostic Network found that about one-third of individuals evaluated fell at or below the 10th percentile for growth, and 19% were at or below the 3rd percentile.
Brain and Nervous System Abnormalities
This is the broadest and most consequential category. It can be satisfied in several ways: a small head circumference (below the 10th percentile), visible brain abnormalities on imaging, neurological problems like seizures or motor impairments, or significant deficits on cognitive and functional testing. Children who score in the bottom 3% on global cognitive tests, or who show significant deficits across multiple functional areas, meet this criterion.
Cognitive and Behavioral Effects
The brain damage from prenatal alcohol exposure creates a wide range of difficulties that go far beyond a lower IQ score. Many of these challenges look like behavioral problems to teachers and parents, but they stem from the way the brain was built.
Executive functioning is one of the most commonly affected areas. This includes the ability to plan ahead, resist impulses, hold information in mind while solving a problem, and shift between tasks. Children with FAS often struggle to organize their schoolwork, follow multi-step instructions, or adjust their behavior when a situation changes. Attention problems are also common, though they differ somewhat from typical ADHD. Children with FAS tend to have particular difficulty encoding new information and flexibly shifting their focus.
Motor skills, both fine and gross, are frequently impaired. Visual-motor coordination, the ability to guide hand movements based on what the eyes see, is especially vulnerable. Social skills present another major challenge. People with FAS often have difficulty reading facial expressions, understanding sarcasm or social cues, and grasping the unspoken rules of human interaction. This can lead to social isolation even when the person is friendly and eager to connect. Memory deficits, sensory sensitivities (such as being bothered by certain textures or sounds), and difficulty responding to typical parenting strategies round out a complex picture.
How Common FAS Is
Prevalence depends heavily on how you look for it. CDC studies using medical records have identified roughly 1 infant with FAS per 1,000 live births in certain parts of the United States. A more recent records-based study found a lower rate of 0.3 per 1,000 among children aged 7 to 9. But studies that send trained examiners into schools to evaluate children directly find much higher numbers: 6 to 9 per 1,000. The gap suggests that FAS is significantly underdiagnosed. Many children with the condition are never identified through routine medical care, particularly if their facial features are subtle or their growth is less affected.
Challenges in Adulthood
FAS is not something children outgrow. The brain differences are permanent, and while people can develop coping strategies, the underlying vulnerabilities persist. Adults with FAS face elevated risks for what researchers call secondary conditions: problems that aren’t caused directly by the brain damage but develop because of it. More than one-third of people with fetal alcohol spectrum disorders develop alcohol or drug problems of their own, and over half of those need inpatient treatment. Disrupted schooling, difficulty holding jobs, and trouble with the legal system are also disproportionately common, often driven by the combination of impulsivity, poor social judgment, and difficulty understanding consequences.
FAS Versus Other Fetal Alcohol Spectrum Disorders
FAS sits at one end of a spectrum. The umbrella term FASD covers several related conditions, including alcohol-related neurodevelopmental disorder (ARND) and alcohol-related birth defects (ARBD). ARND involves the brain and behavioral problems without the characteristic facial features or growth deficiency. ARBD involves physical birth defects, such as heart or kidney abnormalities, linked to alcohol exposure. FASD itself is not a diagnosis you receive. It’s a category that groups these related diagnoses together. A person can have significant brain damage from prenatal alcohol exposure without meeting the full criteria for FAS, which is why the broader spectrum matters.
Interventions That Help
There is no cure for FAS, but several structured programs have shown measurable benefits. These tend to work best when they involve both the child and the caregiver, and when they’re tailored to the specific way FAS affects thinking and behavior rather than using generic behavioral approaches.
One program called Parents and Children Together (PACT) uses techniques from brain injury rehabilitation to help children improve self-regulation and executive function over 12 weekly sessions. It teaches children to recognize their own behavioral state, using the metaphor “how does my engine run?” and gives them specific strategies for adjusting it. Families Moving Forward is a longer-term program, lasting 9 to 11 months, that works with caregivers of children who have severe behavioral challenges. Rather than treating the child directly, it equips parents with positive behavior support techniques through biweekly 90-minute sessions.
For academic challenges, the Math Interactive Learning Experience (MILE) program provides six weeks of one-on-one tutoring using adapted materials like vertical number lines and timers, paired with parent training on behavioral regulation. Social skills are addressed through programs like Good Buddies, a 12-week friendship training program that teaches age-appropriate social skills and builds toward each child hosting a supervised play date with a peer. Early identification gives children the best chance to benefit from these interventions, since building skills on a foundation is easier than trying to retrofit them later.
Prevention
There is no known safe amount of alcohol during pregnancy, and there is no safe trimester to drink. The brain develops throughout the entire pregnancy, so alcohol can cause harm at any stage. Because many pregnancies are unplanned, the CDC also advises that people who are trying to become pregnant avoid alcohol entirely. FAS is the leading preventable cause of intellectual disability, and the only certain way to eliminate the risk is to not drink during pregnancy.