In a fetus at risk of severe Rh haemolytic disease, which sonographic finding is the EARLIEST indicator of developing hydrops fetalis?
- A Skin oedema of the scalp and trunk
- B Pericardial effusion
- C Placental thickness greater than 4 cm with polyhydramnios ✓
- D Marked ascites with hepatomegaly
Correct answer: C. Placental thickness greater than 4 cm with polyhydramnios
Explanation
Before frank hydrops appears, the anaemic fetus develops high-output cardiac changes and hepatic extramedullary erythropoiesis, producing placental thickening exceeding 4 cm and increasing amniotic fluid volume. These precede serous cavity effusions and skin oedema, which define established hydrops. Recognising these earlier markers prompts intensified Doppler surveillance and timely intrauterine transfusion before decompensation occurs.
Reference: Ian Donald's Practical Obstetric Problems, 8th ed.
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