Fetal Hemodynamic Response to Anemia in Early Gestation: Using Hemoglobin Bart's Disease as a Study Model.

 Fetal anemia induces hypervolemia and increases cardiac output to meet the tissue oxygen requirement, resulting in an increase in size without hypertrophy, volume load without pressure load, and a decrease in the globular sphericity index. The heart works very well but works harder, especially systolic ventricular load. Hydrops fetalis due to anemia appears not to be caused by heart failure as previously believed but rather by volume load with high vascular permeability at least in early pregnancy.