Chapter 1: Foundations of Fetal Echocardiography Screening

1.1 Indications for Screening

Fetal echocardiography is indicated when maternal, familial, or fetal factors suggest an elevated risk for CHD. Identifying these indications ensures that high-risk pregnancies receive timely and specialized cardiac evaluation. Risk stratification improves detection rates and supports targeted referral pathways.

Fetal echocardiography is indicated when risk factors for CHD are present. These can be classified into maternal, familial, and fetal categories.

Risk Category	Examples	Estimated Risk of CHD
Maternal	Pre-gestational diabetes, Lupus (anti-SSA/SSB), teratogen use	3–5%
Familial	CHD in parent/sibling, genetic syndromes	2–18%
Fetal	Abnormal 4-chamber/3VTV, extracardiac anomaly, arrhythmia, hydrops	20–50%

Chart 1. Indications for Fetal Echocardiography

1.2 Standard Screening Views

Successful fetal cardiac evaluation relies on consistent use of standardized imaging views. The four-chamber, outflow tracts, and three-vessel and trachea views form the foundation of screening, with additional views obtained as needed. Understanding what each view demonstrates and which anomalies can be detected is critical for accurate interpretation.

Fetal echocardiographic studies should include both still and moving images, accompanied by a structured report. Required motion clips include but are not limited to the following³:

Axial sweep from the stomach to the upper mediastinum, to include the four-chamber view, arterial outflow tracts, as well as the great vessel and arch views
Four-chamber view: 2D and color Doppler ultrasound
Left ventricular (LV) outflow tract view: 2D and color Doppler ultrasound
Right ventricular (RV) outflow tract view: 2D and color Doppler ultrasound
3VV and 3VT views: 2D and color Doppler ultrasound
Sagittal view of the aortic and ductal arches: 2D and color Doppler ultrasound

View	What It Shows	Clinical Significance
4-Chamber	Ventricular size & symmetry	Detects 30–40% of CHD
LVOT	LV outflow, aortic continuity	Detects conotruncal anomalies
RVOT	RV outflow, pulmonary artery	Detects TOF, TGA
3-Vessel + Trachea	PA, Ao, SVC relationship	Detects arch anomalies
Arches	Aortic & ductal arches	Assesses coarctation, interrupted arch

Chart 2. Screening Views and Clinical Significance

Below is a step-by-step guide to the essential views and structures that must be evaluated during a comprehensive fetal echocardiogram. Each section highlights what to see, what to check, and how to use Doppler for confirmation³.

1. Abdominal Situs

1st Trimester-Dextrocardia

Purpose: Establish left–right orientation and confirm normal organ arrangement.
How:
- Begin with a transverse view of the upper abdomen.
- Identify the stomach (left side), liver/gallbladder (right side), aorta, and systemic veins.
Tip: As you sweep cephalad toward the thorax, visualize the hepatic veins and their connections.

2. Four-Chamber View

Purpose: Foundation view for heart structure and function.
What to assess:
- Cardiac position and axis
- Chamber size (atria/ventricles)
- Septal anatomy (atrial and ventricular)
- AV valve structure
- Pulmonary venous return
Use Doppler to check:
- AV valve regurgitation
- Flow direction at foramen ovale
- Ventricular septal integrity
- Pulmonary venous inflow

3. Left Ventricular Outflow Tract (LVOT)

Purpose: Assess aortic valve and outflow.
How: Angle cephalad from the 4-chamber view.
What to see: Subaortic region, aortic valve, ascending aorta.
Use Doppler to check: Aortic regurgitation or obstruction.

4. Right Ventricular Outflow Tract (RVOT)

Purpose: Evaluate pulmonary valve and proximal pulmonary arteries.
What to see: Subpulmonary region, pulmonary valve, main pulmonary artery, bifurcation.
Use Doppler to check: Pulmonary valve stenosis or regurgitation.

5. Three-Vessel View (3VV)

Purpose: Compare size, alignment, and arrangement of the great vessels.
What to see: From left to right – main pulmonary artery, ascending aorta (cross-section), superior vena cava (SVC).
Tip: Look for abnormal vessel number, size, or arrangement.

6. Three-Vessel Trachea View (3VTV)

Purpose: Visualize arches relative to the trachea.
What to see: Aortic and ductal arches running parallel to the trachea, converging into descending aorta.
Use Doppler to check: Patency and direction of flow.

7. Bicaval View

Purpose: Confirm systemic venous return.
What to see: IVC and SVC in sagittal plane.
Use Doppler to check:
- Foramen ovale patency and flow direction
- Rule out interrupted IVC

8. Long-Axis View of the Aortic Arch

Purpose: Assess continuity and caliber of arch segments.
What to see: Ascending aorta → transverse arch → isthmus → descending aorta.
Use Doppler to check: Antegrade systolic flow; minimal diastolic forward flow.

9. Long-Axis View of the Ductal Arch

Purpose: Evaluate ductus arteriosus and its connections.
What to see: Ductal arch from pulmonary artery to descending aorta.
Use Doppler to check: Flow velocity and direction; assess for ductal restriction.

10. Short-Axis Views

Purpose: Assess ventricular septum, AV valves, and outflow tracts.
What to see:
- High short-axis: Aortic valve, RVOT, pulmonary artery bifurcation, tricuspid valve, ventricular septum.
Use Doppler to check:
- Ventricular septal integrity
- Tricuspid regurgitation
  1st Trimester-Tricuspid Regurgitation

1.3 Technical Considerations

Obtaining diagnostic-quality images can be challenging due to fetal position, maternal body habitus, and gestational age. Optimizing technical parameters such as depth, focus, frame rate, and judicious use of Doppler is essential for maximizing accuracy while adhering to ultrasound safety principles³.

1. Frame Rate

Maintain > 30–40 Hz for normal fetal heart rates (120–160 bpm).
Increase to 80–100 Hz (~40 frames/cardiac cycle) for faster heart rates (>140 bpm) or when performing speckle-tracking analysis.

2. Image Magnification & Focus

Adjust magnification so the heart fills ~one-third of the screen.
Position the focal zone at the region of interest for optimal lateral resolution.

3. Septal Imaging

Obtain orthogonal projections.
Ensure septal planes are perpendicular to the ultrasound beam.

4. Doppler Technique

Use Color and Spectral Doppler aligned coaxially with blood flow for:
- Intracardiac shunts
- Valvular flow
- Vascular hemodynamics
Apply Power Doppler to enhance visualization of:
- Small vessels
- Flow across septal defects

5. When Imaging Is Limited

If diagnostic quality cannot be achieved, schedule a repeat study.
Document limitations clearly in the structured report.

Fetal Echocardiography Screening Essentials: Technique, Protocol, and Workflow

Chapter 2: Protocol and Workflow in Clinical Practice