First-trimester screening at 12 weeks reveals increased nuchal translucency and reversed a-wave in the ductus venosus Doppler waveform. Reversal of the ductus venosus a-wave is best explained by which mechanism?
- A Increased placental vascular resistance
- B Obstruction of the umbilical vein at the abdominal wall
- C Elevated central venous pressure transmitted from the right atrium ✓
- D Left ventricular outflow tract obstruction
Correct answer: C. Elevated central venous pressure transmitted from the right atrium
Explanation
The ductus venosus connects the umbilical vein to the inferior vena cava just below the right atrium. During atrial contraction, raised right atrial pressure normally blunts but does not reverse forward flow. In aneuploid fetuses, especially those with cardiac defects, elevated central venous pressure reverses the a-wave, making this waveform an independent marker alongside NT for trisomy 21 and congenital heart disease. Placental resistance affects umbilical, not DV, waveforms.
Reference: Rumack's Diagnostic Ultrasound, 5th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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