FE Cardiac Biometry & Measurements Flashcards

A z-score of −2.0 for the aortic valve annulus diameter means the measurement is:

Answer: 2 standard deviations below the mean for gestational age

A z-score of −2.0 means the aortic annulus is 2 standard deviations below the expected mean for that gestational age or fetal weight, indicating significant hypoplasia.

Fetal ventricular stroke volume is calculated using which formula?

Answer: VTI × cross-sectional area of the outflow tract

Stroke volume = velocity-time integral (VTI) × cross-sectional area (π × r²) of the outflow tract; multiplying by heart rate gives cardiac output.

The normal combined cardiac output (CCO) in a near-term fetus is approximately:

Answer: 300–500 mL/kg/min

Normal fetal CCO (RV output + LV output) is approximately 300–500 mL/kg/min, reflecting the high-output state required for fetal oxygen delivery.

Why are z-scores preferred over absolute measurements when assessing fetal cardiac dimensions?

Answer: They correct for gestational age and fetal size, enabling comparison across different fetuses

Z-scores normalize measurements to gestational age and fetal size so that a dimension can be judged as truly small or large independent of the fetus's overall growth trajectory.

The normal fetal heart rate range throughout most of the second and third trimesters is:

Answer: 120–160 bpm

A normal fetal heart rate of 120–160 bpm is expected throughout the second and third trimesters; rates persistently below 110 bpm or above 180 bpm require evaluation for arrhythmia.

When comparing right and left ventricular dimensions in fetal biometry, a right-to-left ventricular transverse diameter ratio greater than 1.6 most likely suggests:

Answer: Left heart hypoplasia or right heart volume overload

Although the RV is mildly dominant normally (RV:LV ≈ 1.0–1.1), an RV:LV ratio >1.6 raises concern for left heart hypoplasia (e.g., HLHS) or conditions causing right heart volume or pressure overload.

Normal pulmonary vein Doppler in a healthy fetus demonstrates:

Answer: Pulsatile forward flow throughout the cycle, including during atrial contraction

Healthy fetal pulmonary veins show pulsatile yet consistently anterograde flow throughout the cardiac cycle; reversal during atrial contraction indicates elevated left atrial pressure or diastolic dysfunction.