Fetal Heart, Chest, and Abdomen

Quick Answer: Get 4-chamber, LVOT/RVOT, 3-vessel trachea. Stomach left, kidneys both sides, bladder, cord 3 vessels. Great vessel size/order defects flag TGA, TOF. Document incomplete cardiac when fetal position limits.

Cardiac Screening: Beyond the Four-Chamber View

The mid-trimester fetal cardiac survey is screening, not a pediatric echocardiogram—but RDMS items punish candidates who stop after a symmetric four-chamber view. Conotruncal defects (transposition of the great arteries, tetralogy of Fallot, truncus arteriosus) may show normal four-chamber while great vessel arrangement is abnormal.

Four-Chamber View Essentials

Asymmetric chambers, single ventricle appearance, or absent septum suggests major anomaly—MFM fetal echo referral.

Outflow Tract Views

LVOT (left ventricular outflow tract): aortic root arising from left ventricle, crossing toward right.

RVOT (right ventricular outflow tract): pulmonary artery arising from right ventricle.

Sweep from four-chamber toward great vessels—registry images may show only one outflow; question asks next required view.

Three-Vessel Trachea View (3VT)

From left to right (fetal left on screen right in standard orientation):

1. Pulmonary artery (largest, bifurcating)
2. Aorta (circular, smaller)
3. Superior vena cava (smallest)

Trachea appears as hypoechoic ring posterior to vessels. Parallel great vessels instead of crossing pattern suggests TGA. Vessel size discordance suggests TOF or stenosis.

Worked Scenario: Normal Four-Chamber, Abnormal 3VT

4-chamber symmetric but 3VT shows parallel PA and aorta—suspect transposition of the great arteries. Registry correct answer: incomplete cardiac screening if outflows/3VT not obtained; refer for fetal echo.

Heart Rate and Rhythm

Normal fetal heart rate 110–160 bpm. Persistent bradycardia or tachycardia warrants M-mode documentation. Arrhythmias (PACs, SVT) may appear as registry recognition items.

Chest and Diaphragm

Congenital diaphragmatic hernia (CDH):

• Stomach or liver in thorax
• Mediastinal shift
• Reduced lung area
• Often polyhydramnios (swallowing impairment)

Bochdalek posterolateral hernia most common. Liver up in chest suggests poorer prognosis in some staging systems.

Pleural effusions suggest hydrops workup—cardiac, anemia, infection, structural.

Abdominal Situs

Right-sided stomach prompts situs anomaly evaluation—complete cardiac and abdominal situs assessment.

Kidneys and Urinary Tract

Both kidneys in renal fossae with appropriate cortical echogenicity. Measure renal pelvis AP diameter in true AP plane.

Increased renal echogenicity suggests dysplasia—compare to liver.

Umbilical Cord

• Three-vessel cord: two arteries, one vein (vein larger)
• Single umbilical artery (SUA): increased risk of renal and cardiac anomalies—recommend targeted survey
• Document cord insertion (central, marginal, velamentous—see placenta section)

Bowel Echogenicity

Echogenic bowel equal to or greater than bone is a soft marker—may prompt TORCH, CF screening, or aneuploidy correlation depending on protocol. Distinguish from normal slightly bright bowel in early second trimester.

Documentation of Incomplete Cardiac

When outflow tracts or 3VT not visualized due to spine posterior position: document limitation and recommend follow-up or MFM—never "normal fetal heart" when mandatory views missing.

Exam Traps

• Four-chamber alone labeled complete cardiac survey
• Missing SUA on transverse cord slice
• Stomach in chest dismissed as normal fluid
• Ignoring right-sided stomach without situs workup
• Physiologic renal pelvis called hydronephrosis without measurement context

Cardiac registry images reward 3VT mastery—many lethal-appearing situations are incomplete surveys fixable with correct next view.

Fetal Echocardiography Referral Triggers

Refer for fetal echocardiography when: maternal diabetes (preexisting or gestational), SSA/SSB antibodies, family history of congenital heart disease, known fetal arrhythmia, extracardiac anomaly, increased NT, or incomplete screening views after repeat attempt. Registry "next step" items often choose MFM fetal echo over repeating four-chamber alone.

Ventricular Septal Defect Recognition

Small VSD may appear as dropout in interventricular septum on four-chamber view—color Doppler confirms shunt. Large VSD or AV canal defects show gross chamber asymmetry or single ventricle appearance. Outflow tract views remain mandatory even when four-chamber appears symmetric.

Pulmonary Veins and Situs

At least one pulmonary vein entering left atrium should be documented on four-chamber sweep. Total anomalous pulmonary venous return may show normal four-chamber initially—suspicion arises when atria appear abnormal size or 3VT shows abnormal vessel arrangement.

Abdominal Wall Defects

Liver in omphalocele vs bowel only affects prognosis counseling. Gastroschisis shows free-floating bowel loops without hepatic herniation in typical cases.

Bladder and Amniotic Fluid Link

Absent fetal bladder with oligohydramnios suggests bilateral renal agenesis or severe obstruction—Potter sequence concern. Megacystis in male fetus prompts posterior urethral valves evaluation. Document bladder cycle (fills and empties) when possible; persistent megacystis is abnormal.

Diaphragmatic Hernia Staging Clues

Beyond stomach in chest, assess lung-to-head ratio (LHR) in specialized centers—registry may recognize mediastinal shift and polyhydramnios as CDH associations. Contralateral lung hypoplasia worsens prognosis. Document liver position (up vs down) when visible.