Harvey's Garden

Hydrops Fetalis

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  • Definition

    • Severe, pathologic fluid accumulation in ≥2 fetal compartments.
    • Findings include: ascites, pleural effusion, pericardial effusion, and generalized skin edema (>5 mm).
    • Often associated with polyhydramnios and placental thickening.

  • Pathophysiology

    • Disruption of the equilibrium of fetal interstitial fluid production and lymphatic return.
    • Primary mechanisms:
      • High-output cardiac failure (most common, often from severe anemia).
      • Obstructed lymphatic drainage.
      • ↓ Plasma oncotic pressure (e.g., liver failure, congenital nephrosis).
      • ↑ Capillary permeability (e.g., infection).

  • Etiology & Classification

    • Immune Hydrops

      • Caused by erythroblastosis fetalis due to maternal antibody-mediated hemolysis of fetal RBCs.
      • Classic cause: Rh(D) alloimmunization. An Rh(-) mother is sensitized to Rh(+) fetal RBCs from a prior pregnancy or transfusion. Maternal anti-D IgG crosses the placenta during a subsequent pregnancy with an Rh(+) fetus, causing widespread hemolysis.
      • Other causes: Other blood group incompatibilities (e.g., Kell, Duffy).
      • Mechanism: Severe anemia → tissue hypoxia & extramedullary hematopoiesis → hepatosplenomegaly → portal hypertension & ↓ albumin synthesis → high-output heart failure → edema.
      • Prevention: Administration of anti-D immune globulin (RhoGAM) to Rh(-) mothers at ~28 weeks gestation and postpartum.

    • Non-Immune Hydrops (NIHF)

      • Accounts for ~90% of cases today due to the success of RhoGAM.
      • Cardiovascular (~40%): Most common cause of NIHF.
        • Structural anomalies (e.g., hypoplastic left heart syndrome).
        • Arrhythmias (e.g., SVT, complete heart block).
        • High-output states (e.g., sacrococcygeal teratoma, chorioangioma).
      • Chromosomal Aneuploidies (~15%):
        • Turner Syndrome (45,XO) is classic, associated with cystic hygroma and lymphatic dysplasia.
        • Trisomies 21, 18, and 13.
      • Hematologic (~10%):
        • Alpha-thalassemia major (Hb Barts): Fatal form where all 4 alpha-globin genes are deleted. Hb Barts (γ4) has an extremely high O2 affinity, causing severe tissue hypoxia.
        • G6PD deficiency, pyruvate kinase deficiency.
      • Infections (TORCH):
        • Parvovirus B19 is the most common infectious cause. It infects and destroys erythrocyte precursors, leading to severe aplastic anemia and high-output heart failure.
        • Others: CMV, toxoplasmosis, syphilis.

  • Diagnosis

    • Ultrasound: Definitive diagnostic tool. Shows fluid in ≥2 compartments (e.g., scalp edema, ascites).
    • Middle Cerebral Artery (MCA) Doppler: ↑ peak systolic velocity suggests fetal anemia.
    • Maternal Labs: Blood type and antibody screen, TORCH serologies.
    • Amniocentesis: For fetal karyotyping, PCR for infections.

  • Management

    • Directed at the underlying cause.
    • For Anemia: Intrauterine blood transfusion.
    • For Arrhythmia: Transplacental maternal administration of antiarrhythmic drugs (e.g., digoxin, flecainide).
    • Thoracentesis/paracentesis can be performed to relieve pressure.
    • Often requires preterm delivery and intensive neonatal resuscitation.
    • Prognosis: Generally poor, with high perinatal mortality, especially in NIHF with an unknown cause or chromosomal abnormality.

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