Can Fetal Alcohol Syndrome Be Diagnosed on Ultrasound?
No, fetal alcohol syndrome (FAS) cannot be diagnosed on prenatal ultrasound because the diagnosis requires postnatal assessment of three specific facial features (smooth philtrum, thin vermillion border of the upper lip, and small palpebral fissures), growth deficits, and CNS abnormalities—none of which can be reliably identified or measured prenatally. 1
Why Ultrasound Cannot Diagnose FAS
The Diagnostic Criteria Require Postnatal Assessment
FAS diagnosis mandates documentation of all three components that cannot be adequately evaluated in utero 1:
Facial dysmorphology: The three cardinal facial features (smooth philtrum ranked 4-5 on lip/philtrum guide, thin vermillion border ranked 4-5, and palpebral fissures ≤10th percentile) require direct physical examination with standardized measurement tools that do not exist for prenatal imaging 1
Growth deficits: Height and/or weight ≤10th percentile must be plotted on racially/ethnically appropriate growth curves postnatally, as prenatal growth restriction has multiple non-alcohol-related causes (maternal smoking, poor nutrition, genetic disorders) that cannot be differentiated on ultrasound 1
CNS abnormalities: While structural brain anomalies might theoretically be visible on ultrasound, the diagnosis also requires functional and neurologic deficits (performance ≥1.5 SD below mean on neurobehavioral testing, developmental delays, seizures) that can only be assessed after birth 1
What Ultrasound Might Show (But Cannot Confirm FAS)
Nonspecific Findings
Prenatal ultrasound may detect growth restriction or certain structural brain anomalies, but these findings are not diagnostic of FAS because 1:
- Growth restriction occurs in multiple conditions unrelated to alcohol exposure
- Structural brain anomalies can result from numerous genetic and environmental factors
- The characteristic facial features that distinguish FAS from other syndromes cannot be reliably measured prenatally 1
Critical Diagnostic Pitfall
Even if prenatal growth retardation is documented, this alone does not establish FAS diagnosis, as the full constellation of facial dysmorphology and CNS abnormalities must be present postnatally 1. The facial features are particularly important because, with the exception of toluene embryopathy, no other syndrome has the complete triad of small palpebral fissures, thin vermillion border, and smooth philtrum 1.
When to Suspect FAS After Birth
Postnatal Referral Triggers
If substantial prenatal alcohol exposure is known (≥7 drinks per week or ≥3 drinks on multiple occasions), refer for full FAS evaluation when any of the following are present postnatally 1:
- All three facial features present
- One or more facial features with growth deficits
- One or more facial features with CNS abnormalities
- Parental/caregiver concern about possible FAS
The Diagnostic Timeline
Facial features may become less apparent after puberty, making early postnatal diagnosis critical 1. However, growth problems documented at any age, including prenatal growth deficiencies, remain consistent with FAS criteria if other features are present 1.
Clinical Bottom Line
Prenatal ultrasound has no role in diagnosing FAS. The diagnosis is entirely postnatal, requiring direct physical examination with standardized measurement tools for facial features, postnatal growth assessment, and comprehensive neurodevelopmental evaluation 1. If significant prenatal alcohol exposure is documented, close monitoring of growth and development after birth is warranted, but diagnosis cannot be made until the child can be fully assessed postnatally 1.