MFM clinicians & sonographers
Recognize the anatomy. Assess pulmonary blood flow. Translate the findings into a plan for birth.
Use complementary views to identify the TOF pattern.
Define obstruction, vessels, ductal flow, and associated findings.
Communicate uncertainty and coordinate prenatal and neonatal care.
Recognition
The outflow tracts may carry the decisive findings.
Four chambers and balanced ventricular size do not establish normal great-artery connections.
Complete outflow and three-vessel/three-vessel-and-trachea views. Refer a suspected cardiac abnormality for specialist fetal echocardiography.
Anatomic pattern
Look for a malalignment VSD, an overriding aorta, and right ventricular outflow obstruction.
Image acquisition
Establish fetal orientation and situs before interpreting cardiac relationships.
Situs, cardiac position, four chambers, AV junction.
LVOT and RVOT; trace both ventricular outlets.
3VV/3VT, arches, ductus, and pulmonary branches.
LVOT & five-chamber view
An apparent septal gap can be an imaging artifact.
Demonstrate the subaortic VSD and aorta spanning the septum. Trace the outlet from the ventricle rather than interpreting one frozen image.
Change the angle and obtain an orthogonal view. Check grayscale before relying on color; excessive gain can blur boundaries.
RVOT assessment
“Small pulmonary artery” is a starting observation, not a complete assessment.
Assess subvalvar narrowing, valve opening, annulus size, and main pulmonary artery continuity.
Record branch caliber and confluence when visible. State when pulmonary supply or branch anatomy cannot be resolved.
Use the laboratory’s validated measurement method and gestational-age reference. Record the actual dimension, Z-score, and reference model so serial studies can be compared.
3VV & 3VT
Disproportion between the great vessels should trigger a focused outflow assessment.
Tips & tricks
A technical limitation can imitate missing flow or abnormal anatomy.
Hemodynamics
Velocity and aliasing depend on settings, beam alignment, and the amount of flow.
Show flow through the outflow tract and into the overriding aorta. Confirm suspected turbulence with appropriate interrogation.
A single RVOT velocity cannot define all fetal TOF or predict newborn stability. Severe obstruction with very little flow may not produce a dramatic jet.
Ductus arteriosus
Describing anatomy is clearer than labeling color as “forward” or “reverse.”
The usual fetal ductal-flow direction. It does not, by itself, exclude evolving obstruction or later neonatal support.
Raises concern that lung blood supply may depend on an open ductus after birth. Integrate with pulmonary valve and artery findings.
Variant • pulmonary atresia
TOF with pulmonary atresia requires a pulmonary-supply assessment.
Confirm no antegrade continuity/flow from RV to pulmonary artery with optimized views and Doppler.
Assess the ductus, central pulmonary arteries, confluence, and possible major aortopulmonary collateral arteries (MAPCAs).
Variant • absent pulmonary valve
A small annulus may coexist with markedly enlarged pulmonary arteries.
Rudimentary valve function with marked regurgitation and to-and-fro flow.
Enlarged main/branch pulmonary arteries, cardiac function, and signs of compromise.
Consider airway compression and respiratory support needs at birth.
Differential diagnosis
Resolve anatomy across multiple views and seek expert review when the distinction remains uncertain.
| Possibility | Decisive question |
|---|---|
| TOF / DORV with pulmonary stenosis | How do both great arteries connect to the ventricles? Describe the VSD and degree of aortic commitment; an override percentage alone is incomplete. |
| Common arterial trunk | Is there one arterial root supplying systemic, pulmonary, and coronary circulations, rather than two separate outlets? |
| VSD without TOF | Is the RV outflow unobstructed, and is the aortic relationship normal? |
| TOF with AVSD | Is there an abnormal AV junction/common valve in addition to the outflow findings? |
Associated findings
Associated anatomy can change counseling, testing, and neonatal needs.
Assess the AV junction, arch sidedness, venous connections, valve function, rhythm, and ventricular function.
Review extracardiac anatomy and growth. Evaluate the thymus when feasible and look for other features that inform genetic counseling.
Genetic evaluation
Testing informs more than the cardiac surgical plan.
Discuss the phenotype, family history, patient preferences, and test limitations.
Diagnostic testing with chromosomal microarray for the structural anomaly.
Consider additional sequencing with genetics when the phenotype or prior results support it.
Surveillance
Ask what could change the delivery or newborn plan.
Individualize follow-up with fetal cardiology. Progressive obstruction, uncertain pulmonary supply, or functional concerns require closer reassessment.
Evidence appraisal
Vetten et al., 2025: retrospective multicenter cohort of 253 infants with simple TOF.
Measurements at 28–32 weeks; early intervention meant a procedure within 30 days after birth. 33 infants (13%) had early intervention.
PV Z-score ≤ −3.5 OR abnormal ductal flow: sensitivity 79%, specificity 70%.
Delivery planning
Document actual capabilities and transfer access, not only a hospital level designation.
Agree on newborn assessment, timely echo, cardiology access, and escalation if the postnatal findings differ.
Coordinate delivery where stabilization, PGE1 when indicated, and the required cardiac/airway expertise are available.
Neonatal handoff
The receiving team needs the anticipated physiology and a contingency plan.
Specify subtype, expected pulmonary supply, and unresolved anatomy.
Plan examination, oxygenation assessment, echo, and PGE1 for suspected ductal dependence.
Identify neonatal/cardiology contacts, delivery location, and transport or intervention arrangements.
After birth
Counsel families about the pathway without promising a single operation date.
Elective complete repair is commonly planned in infancy; AATS consensus supports 3–6 months for asymptomatic infants.
Earlier repair or staged palliation may be appropriate. Pulmonary supply, comorbidities, size, and center expertise shape the approach.
Reporting & escalation
A useful report distinguishes a finding from its interpretation.
Practice • hypothetical cases
These cases illustrate reasoning; they are not patient records or stand-alone risk calculators.
Malalignment VSD and overriding aorta; antegrade pulmonary flow; PA-to-aorta ductal flow; preserved function.
Similar intracardiac pattern; very small pulmonary valve and aorta-to-PA ductal flow.
Both require specialist confirmation, genetic counseling, and follow-up. Case A still needs serial evaluation and a newborn plan. Case B raises greater concern for ductal-dependent pulmonary blood flow: reassess anatomy, coordinate delivery capabilities, and establish PGE1/stabilization readiness. Neither is classified solely by one number.
Clinical pearls
Remember the actions that make the diagnosis useful.
A normal four-chamber view does not clear the outflow tracts.
Reproduce findings in more than one plane.
Poor settings can mimic absent flow.
Name ductal flow by its source and destination.
Separate screening from diagnostic testing.
Specify team, location, actions, and uncertainty.
Evidence & controversies
Use evidence to support judgment, and name its limits.
Multiplanar anatomy, pulmonary flow assessment, genetic evaluation, and coordinated perinatal care guide practice.
No single cut-off predicts every newborn’s needs. Measurement models, phenotype, and referral selection affect risk estimates.
Prospective external validation of prediction models, standardized measurements, and phenotype-specific genetic and long-term outcomes.
References • 1 of 2
Guideline recommendations and expert clinical synthesis.
References • 2 of 2
Reviewed September 17, 2026. Interpret each source within its population and evidence type.