Nonimmune Hydrops Fetalis
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Nonimmune hydrops fetalis (NHF) is the presence of excessive fluid in two or more fetal compartments (for example, skin edema, pleural effusion, pericardial effusion, or ascites), in the absence of red cell alloimmunization. NHF accounts for 90% of cases and occurs in 1/1,700-1/3,000 pregnancies. The pathophysiologic fetal mechanisms resulting in hydrops, include increased right heart pressure, inadequate ventricular filling, obstruction of blood or lymphatic flow, hepatic venous congestion leading to hypoalbuminemia, increased capillary permeability, and anemia. A thorough antenatal or postnatal evaluation results in a diagnosis in approximately 85% of cases. Cardiovascular etiologies are most common, in 17-35% of cases. Chromosomal abnormalities, especially 45X and trisomy 21, account for 7-16%. Fetal anemia accounts for 4-12%. Less common causes include lymphatic dysplasia (5-6%), fetal tumors (2-3%), skeletal dysplasia (3-4%) and fetal gastrointestinal (0.5-4%) and urinary tract anomalies (2-3%). Twin-twin transfusion syndrome is another etiology.
The diagnostic evaluation begins with taking maternal and family histories, medication usage, and other exposures. An antibody screen to exclude alloimmunization is essential. The Kleihauer-Betke smear to assess for fetomaternal hemorrhage, test for parvovirus infection, and parental evaluation for hemoglobinopathy risk, especially alpha thalassemia, should be considered.
Additional detailed fetal sonography of the fetus and placenta is necessary, including fetal echocardiography and middle cerebral artery Doppler studies to evaluate for anemia. A fetal karyotype, with chromosomal microarray analysis, is indicated despite the identification of a structural fetal anomaly. 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 can confer a poor prognosis. Neonatal survival is often less than 50%. Management may include pregnancy termination, therapeutic interventions when appropriate, and supportive care as needed. Preterm delivery could occur for fetal and obstetric indications. Antepartum surveillance is necessary to identify fetal deterioration. 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. In most cases, mirror syndrome necessitates delivery. These pregnancies should be delivered at a facility with the capability to stabilize and treat the underlying etiology of these critically-ill newborns.
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 Sept 2021. Revised March 2023
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