Abnormal accumulation of fluid in 2 sites (pleural, pericardial, ascites, skin)

Pleural effusion surrounds lung, which floats toward hilum: Angel wing sign

Large pericardial effusion surrounds heart, displaces lungs to chest wall

Polyhydramnios, placentomegaly may be seen but do not count toward areas of excess fluid accumulation

Look for structural abnormalities: Hydrops may be due to chromosomal abnormality, infection, vascular malformation, skeletal dysplasia

Do not confuse hypoechoic abdominal wall muscles with small volume of ascites

Do not confuse hypoechoic, compacted peripheral myocardium with pericardial effusion

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  Myocardium ends at valves, effusion surround atria as well as ventricles

Check cardiac rate and rhythm

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  Place M-mode cursor through 1 atrium/1 ventricle to assess atrioventricular conduction

  
  
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  Apparently isolated ascites may be sign of impending hydrops in fetus with tachycardia

In any fetus with hydrops, measure middle cerebral artery (MCA) peak systolic velocity (PSV)

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  MCA PSV increases with fetal anemia

  
  
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  Anemia is treatable cause of hydrops

Scan technique is critical for measurement of MCA PSV

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  Small sample volume placed within 2 mm of takeoff of MCA from circle of Willis

  
  
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  Angle of insonation must be 0, fetus at rest

  
  
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  Measure PSV and plot multiples of median for gestational age (> 1.5 indicates fetal anemia)