Nonimmune hydrops fetalis part I: etiology and pathophysiology.

Nonimmune hydrops fetalis (NIHF) is a condition in which excess fluid has accumulated in the fetal interstitial spaces as a result of one or more nonimmune factors. A plethora of maternal, placental, and fetal disease processes have been associated with NIHF. Knowledge of the various etiologies of NIHF and how the disease process affects fluid homeostasis is important for planning patient care and counseling families of patients diagnosed with nonimmune hydrops fetalis. This article discusses the mechanisms governing fluid distribution in the extracellular spaces, examines the various etiologies associated with NIHF, and describes the pathogenesis of NIHF for each etiologic category.