Fetal hydrops and other variables associated with the fetal hematocrit decrease after the first intrauterine transfusion for red cell alloimmunization

Objective: To evaluate the influence of fetal hydrops and other variables on fetal hematocrit (Hct) decrease after the first intrauterine transfusion (IUT) in alloimmunized pregnancies. Methods: From 1996 to 2006, the data of all alloimmunized pregnancies submitted to IUT were assessed. Exclusion criteria included: fetuses submitted to intraperitoneal transfusion; pregnancies complicated by other fetal abnormalities; pregnancies submitted to only one IUT, and cases in which posttransfusion or pretransfusion blood samples were not obtained. Linear regression models were implemented to assess the relationship between the rate of Hct fall after the first IUT and the following variables: fetal hydrops; antibody titer; gestational age at the first IUT; number of days between the first and second IUT; pretransfusion and posttransfusion fetal Hct values. Results: Fifty fetuses fulfilled the study criteria. The fetal Hct decrease after the first IUT was 1.21 (range 0.18–2.3) %/day. The variables independently associated with the fetal Hct drop after the first IUT were the fetal hydrops (p = 0.000), the pretransfusion fetal Hct (p = 0.001) and the posttransfusion fetal Hct (p = 0.016). Conclusion: Fetal hydrops, pretransfusion fetal Hct and posttransfusion fetal Hct seem to influence the fetal Hct decrease between the first and second IUT. These findings may be helpful for estimating the rate of fetal Hct drop and programming the following IUT.