Prediction of hematocrit decline after intravascular fetal transfusion

Fetal blood sampling and intravascular transfusion via cordocentesis allow more precise fetal evaluation and treatment in isoimmunized pregnancies. However, the timing of repeat transfusion has remained empiric. In this report we review our experience with fetal transfusions in isoimmunized pregnancies to evaluate the ability to predict fetal hematocrit decline and thereby determine the optimum timing for repeat transfusions. Between March 1986 and March 1988, 60 intravascular fetal transfusions were performed in 20 patients. Fetal transfusions were excluded from analysis if blood samples were unable to be obtained before and after transfusion, as well as at the beginning of the next transfusion or birth. Fifty-three procedures were analyzed. Two equations were used to predict the fetal hematocrit at the subsequent transfusion. The difference between observed and predicted hematocrits at the beginning of a subsequent transfusion or birth was -0.9% +/- 5.8% with equation 2, which was the more accurate formula in the majority of fetuses. Prediction of fetal hematocrit decline may be used to determine the optimum timing of repeat transfusion.