Overview
Definition:
Fetal echocardiography is a specialized ultrasound examination performed during pregnancy to assess the structure and function of the fetal heart
It is the gold standard for prenatal diagnosis of congenital heart disease (CHD), allowing for early identification of cardiac malformations and risk stratification.
Epidemiology:
Congenital heart defects (CHDs) are among the most common birth defects, affecting approximately 8-10 per 1000 live births worldwide
A significant proportion of these are diagnosed prenatally through fetal echocardiography, enabling timely intervention and improved outcomes.
Clinical Significance:
Early detection of CHD via fetal echo is crucial for several reasons: it allows for parental counseling, planning of delivery at a tertiary care center with specialized neonatal cardiac services, initiation of antenatal medical management (e.g., prostaglandin infusions), and preparation for postnatal surgical or interventional procedures
It also helps in identifying fetuses at higher risk for genetic syndromes or chromosomal abnormalities.
Indications For Fetal Echo
Maternal Risk Factors:
Maternal diabetes mellitus, maternal phenylketonuria (PKU), maternal infections (e.g., rubella, cytomegalovirus), maternal drug or alcohol exposure, advanced maternal age (>35 years).
Family History:
Previous child with CHD, parental history of CHD, known genetic syndromes associated with CHD (e.g., Down syndrome, Turner syndrome).
Fetal Abnormalities:
Abnormalities detected on routine obstetric ultrasound (e.g., nuchal translucency, extracardiac anomalies), fetal arrhythmias, hydrops fetalis, oligohydramnios, polyhydramnios.
Multiple Gestation:
Discordant growth in monochorionic twins, suspected cardiac anomalies.
Diagnostic Approach
Timing Of Examination:
Ideally performed between 18-24 weeks of gestation for optimal visualization
Can be performed earlier (from 14 weeks) for high-risk pregnancies, but resolution may be limited.
Equipment And Technique:
High-resolution ultrasound equipment with Doppler capabilities is essential
Standardized views of the fetal heart are obtained, including the four-chamber view, outflow tracts, and aortic arch views
Experienced sonographers and cardiologists are key.
Standard Views:
Four-chamber view (diaphragm, ventricles, atria, mitral valve)
Left ventricular outflow tract (LVOT) view (aorta arising from LV)
Right ventricular outflow tract (RVOT) view (pulmonary artery arising from RV)
Three-vessel view (superior vena cava, aorta, pulmonary artery)
Aortic arch view
Ductal arch view.
Doppler Assessment:
Pulsed and continuous wave Doppler are used to assess blood flow velocities, direction, and patterns across valves and great vessels
Color Doppler helps visualize flow and detect shunts or regurgitation.
Common Chd Detected Prenatally
Conotruncal Anomalies:
Transposition of the great arteries (TGA), Tetralogy of Fallot (TOF), truncus arteriosus
These often present with abnormal outflow tracts.
Atrioventricular Septal Defects:
AVSD (endocardial cushion defects) are commonly associated with trisomy 21
The four-chamber view is critical for their detection.
Ventricular Septal Defects:
VSDs, especially large ones, may be detectable
Small perimembranous or muscular VSDs can be missed and are more challenging to diagnose prenatally.
Hypoplastic Left Heart Syndrome:
HLHS is characterized by a small left ventricle, mitral atresia/stenosis, aortic atresia/stenosis, and hypoplastic ascending aorta
Typically seen in the four-chamber and LVOT views.
Coarctation Of The Aorta:
Can be difficult to diagnose reliably
Findings may include discrepancy in ventricular size, disproportionate great artery sizes, and abnormal flow patterns in the aortic arch.
Pulmonary Atresia:
Absence or severe narrowing of the pulmonary valve, often with associated VSD and right ventricular hypoplasia
RVOT view is critical.
Risk Stratification And Management Implications
High Risk Chd:
CHDs requiring immediate postnatal intervention (e.g., HLHS, critical coarctation, TGA with VSD) warrant delivery at a center with advanced neonatal cardiac care
Prostaglandin infusion post-delivery is often critical.
Moderate Risk Chd:
CHDs with less immediate urgency but requiring specialized care (e.g., certain VSDs, ASDs, mild coarctation) allow for more flexible delivery planning.
Isolated Chd Vs Syndromic:
The presence of extracardiac anomalies or chromosomal abnormalities can influence prognosis and management decisions, requiring a multidisciplinary approach.
Parental Counseling:
Thorough counseling by pediatric cardiologists, neonatologists, and geneticists is essential to discuss the diagnosis, prognosis, treatment options, and potential long-term implications.
Limitations And Challenges
Missed Diagnoses:
Smaller defects (e.g., small VSDs, ASDs), some complex lesions with subtle findings, or those that develop postnatally can be missed
Fetal position and maternal body habitus can also affect image quality.
Interobserver Variability:
Interpretation of findings can vary between examiners, highlighting the need for standardized protocols and experienced personnel.
Interpretation Of Flow Patterns:
Complex flow dynamics in fetal circulation can sometimes be challenging to interpret, especially in the presence of arrhythmias or other fetal conditions.
Follow Up After Birth:
Even with normal fetal echo, a postnatal cardiac evaluation is recommended, particularly for fetuses with risk factors for CHD.
Key Points
Exam Focus:
DNB and NEET SS exams will focus on indications for fetal echo, standard views, common CHDs detected, and the implications of prenatal diagnosis on postnatal management
Understanding risk stratification is key.
Clinical Pearls:
Always correlate fetal echo findings with routine obstetric ultrasound
Be aware that the absence of a VSD on fetal echo does not rule out its presence postnatally
Discuss cases with complex findings with senior neonatologists and cardiologists early.
Common Mistakes:
Mistaking common fetal structures for cardiac anomalies
Inadequate Doppler assessment of outflow tracts
Over-reliance on single views without assessing the entire heart
Failing to consider the clinical context (maternal/fetal risk factors).