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Nonimmune Hydrops Fetalis

Author: Ralph K. Tamura, MD

Editor: Timothy Klatt, MD, Elizabth Ferries-Rowe, MD

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Nonimmune hydrops fetalis is diagnosed with the presence of excessive fluid in two or more fetal compartments (skin edema, pleural effusion, pericardial effusion, and/or ascites) in the absence of red cell alloimmunization.  It accounts for 90% of all cases of hydrops and occurs in 1/1,700-1/3,000 pregnancies.   The differential diagnosis is extensive as several fetal mechanisms are thought to generate hydrops, including increased right heart pressure, inadequate ventricular filling, obstruction of blood or lymphatic flow, hepatic venous congestion leading to hypoalbuminemia, increased capillary permeability, and anemia.   After a thorough evaluation, including that possible postnatally, a cause can be identified for approximately 85% of cases.  Cardiovascular etiologies are most likely, resulting in 17-35% of cases.  Chromosomal abnormalities, especially 45X and trisomy 21, account for 7-16%.  Fetal anemia, resulting from various etiologies, accounts for 4-12%.  Less common causes include lymphatic dysplasia (5-6%), fetal tumors (2-3%), skeletal dysplasias (3-4%) and fetal gastrointestinal (0.5-4%) and urinary tract anomalies (2-3%).  Twin-twin transfusion syndrome is another etiology.  

Once diagnosed, evaluation begins with a maternal history, including family history, medications and exposures.  An antibody screen to exclude alloimmunization is essential. At this time, a Kleihauer-Betke smear to assess for fetomaternal hemorrhage, testing for parvovirus infection, and parental evaluation for hemoglobinopathy risk, especially alpha thalassemia, should be considered. 

When the antibody screen returns unremarkable, extensive, detailed sonography of the fetus(es) and placenta are indicated.  This includes fetal echocardiography with investigation for fetal arrhythmia and middle cerebral artery Doppler studies to evaluate for anemia.  A fetal karyotype, obtained via invasive testing, usually with chromosomal microarray analysis, is indicated regardless of whether a structural fetal anomaly is identified.  Depending on the findings, further testing may include amniotic fluid alpha fetoprotein, PCR for CMV and toxoplasmosis, and fetal blood sampling.

The prognosis depends on the underlying etiology, response to therapy if treatable, and the gestational age at detection and delivery. Aneuploidy confers a poor prognosis, and even in the absence of aneuploidy, neonatal survival is often less than 50%.  Management may include pregnancy termination, therapeutic interventions when appropriate, and supportive care as needed.  Preterm delivery is recommended only for obstetric indications.  Antepartum surveillance should be considered when an etiology amenable to prenatal or postnatal treatment has been identified, in idiopathic cases, and when intervention is planned should fetal deterioration occur. Polyhydramnios and preterm birth occur frequently.  Mirror syndrome, an uncommon complication where the mother develops edema that “mirrors” that of the hydropic fetus, may be a variant of preeclampsia. A few case reports describe the resolution of mirror syndrome with treatment of the etiology of the nonimmune hydrops fetalis.  This approach should only be taken with caution.  In most cases, including idiopathic cases, mirror syndrome necessitates delivery.  These pregnancies should be delivered at a facility with the capability to stabilize and treat the underlying etiology or, if idiopathic, critically ill newborns.

Further Reading:

Society for Maternal-Fetal Medicine (SMFM), Norton ME, Chauhan SP, Dashe JS. Society for maternal-fetal medicine (SMFM) clinical guideline #7: nonimmune hydrops fetalis. Am J Obstet Gynecol. 2015 Feb;212(2):127-39. doi: 10.1016/j.ajog.2014.12.018. Epub 2014 Dec 31.

Initial approval January 2009; Revised January 2018. Reaffirmed July 2019. Revised July 2021.


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