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December 2021- FETAL HYDROPS

Patient presents for detailed fetal anatomical survey at 22 weeks gestation.  Image A is an axial view of the fetal head with evidence of scalp edema. Image B is an axial view of the fetal abdomen demonstrating the presence of abdominal ascites.


The definition of fetal hydrops includes fluid in at least two extravascular compartments.

These compartments include:

  • Pericardial effusion
  • Pleural effusion
  • Ascites
  • Generalized skin edema

Placentomegaly and polyhydramnios are often identified in cases of fetal hydrops but are not required for the diagnosis.

When concerns for fetal hydrops arise, the first step is to determine if the etiology is of an immune or non-immune nature. Immune hydrops is usually due to red blood cell alloimmunization and is usually noted when an indirect Coombs Test (i.e. antibody screen) is performed that detects an antibody that can result in fetal hydrops. When the hydrops is not found to be due to red blood cell alloimmunization, it is referred to as non-immune hydrops (NIH). The prevalence of NIH ranges from 1 in 1700 to 1 in 3000 pregnancies, and NIH accounts for approximately 90% of all cases of fetal hydrops.  There are many etiologies of NIH, however only 60% are detected prenatally.

When fetal hydrops is encountered and found to be non-immune, the first step is to perform a detailed fetal anatomical survey and fetal echocardiogram to assess for structural anomalies as the cause of the hydrops.  Fetal cardiovascular disease is the primary cause of NIH, noted in approximately 20% of cases.

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Society for Maternal-Fetal medicine (SMFM) Clinical Guideline #7: Nonimmune Hydrops Fetalis.
Norton ME, Chauhan SP, Dashe JS. Am J Obstet Gynecol 2015; 212:127–139.

Berger VK, Sparks TN, Jelin AC, et al. Non-Immune Hydrops Fetalis: Do Placentomegaly and Polyhydramnios Matter?  J Ultrasound Med 2018;37(5):1185-1191.