FE FE Cardiac Biometry & Measurements 1 — Questions and Answers
Question 1: What is the normal cardiothoracic area ratio (CTR) in a normal fetus on the four-chamber view?
- Less than 0.20
- Less than 0.33 (approximately 1/3 of thoracic area) (Correct answer)
- Less than 0.50
- Less than 0.60
Correct answer: Less than 0.33 (approximately 1/3 of thoracic area)
The fetal heart normally occupies less than one-third of the thoracic cross-sectional area, giving a cardiothoracic area ratio of less than 0.33.
Question 2: The normal fetal cardiac axis (angle of the interventricular septum relative to the anterior-posterior midline) is approximately:
- 30° ± 5° to the left
- 45° ± 20° to the left (Correct answer)
- 60° ± 5° to the left
- 90° ± 15° to the left
Correct answer: 45° ± 20° to the left
Normal fetal cardiac axis is approximately 45° ± 20° to the left of the midline (range 25–65°); deviation outside this range warrants further evaluation.
Question 3: In fetal cardiac biometry, z-scores normalize measurements primarily against which parameter?
- Crown-rump length only
- Head circumference only
- Estimated fetal weight or gestational age (Correct answer)
- Abdominal circumference only
Correct answer: Estimated fetal weight or gestational age
Z-scores express how many standard deviations a measurement is from the mean for a given estimated fetal weight or gestational age, allowing size-independent comparison.
Question 4: The mitral and tricuspid valve annulus diameters are most accurately measured in which view and at which phase of the cardiac cycle?
- Long-axis view at peak systole
- Four-chamber view at end-diastole (Correct answer)
- Short-axis view at mid-systole
- Five-chamber view at end-systole
Correct answer: Four-chamber view at end-diastole
Atrioventricular valve annuli are measured in the four-chamber view at end-diastole (maximal opening), which provides the most reproducible and clinically relevant dimension.
Question 5: When measuring the aortic valve annulus by fetal echocardiography, the standard technique is:
- End-diastole, leading edge to leading edge
- Peak systole, inner edge to inner edge (Correct answer)
- Mid-systole, outer edge to outer edge
- End-systole, inner edge to outer edge
Correct answer: Peak systole, inner edge to inner edge
Semilunar valve annuli (aortic and pulmonary) are measured at peak systole using inner-edge to inner-edge technique, when the leaflets are maximally open.
Question 6: In normal fetal circulation, the main pulmonary artery (MPA) to aorta (Ao) diameter ratio is approximately:
- 0.7–0.8 (aorta larger)
- Exactly 1.0 (equal size)
- 1.1–1.3 (pulmonary artery slightly larger) (Correct answer)
- 1.5–2.0 (pulmonary artery much larger)
Correct answer: 1.1–1.3 (pulmonary artery slightly larger)
The fetal MPA is normally slightly larger than the aorta (ratio ~1.1–1.3) because the right ventricle carries the higher combined ventricular output through the ductus arteriosus.
Question 7: What is the expected right ventricular (RV) to left ventricular (LV) size relationship in a normal fetus on the four-chamber view?
- LV is clearly larger (RV:LV ≈ 0.6–0.7)
- Approximately equal, with the RV mildly dominant (RV:LV ≈ 1.0–1.1) (Correct answer)
- RV is markedly larger (RV:LV ≈ 1.5–2.0)
- LV is always dominant after 28 weeks
Correct answer: Approximately equal, with the RV mildly dominant (RV:LV ≈ 1.0–1.1)
In fetal life the two ventricles are approximately equal in size with mild right-sided dominance (RV:LV ≈ 1.0–1.1) because the RV ejects the majority of the combined cardiac output.
FE FE Cardiac Biometry & Measurements 1
What is the normal cardiothoracic area ratio (CTR) in a normal fetus on the four-chamber view?