Fetal hematocrit decrease after repeated intravascular transfusions in alloimmunized pregnancies

The aim of this study is to evaluate the fetal hematocrit (Hct) decrease along repeated intravascular intrauterine fetal transfusions (IUTs) and test the hypothesis that, after consecutive IUTs, there is a lower Hct drop off.

From July 1996 to June 2006, pregnancies submitted to IUT for fetal hemolytic anemia treatment had their data assessed. The daily rate of decrease in fetal Hct was calculated by dividing the difference between the posttransfusion Hct of the previous IUT and the pretransfusion Hct of the current IUT, by the number of days between the transfusions. Fetuses with other abnormalities or submitted to intraperitoneal transfusions were excluded.

Eighty-one women were submitted to IUT during the alluded period, ensuing 296 intrauterine transfusions. The perinatal survival was 89.9% (n = 80), with 92.0% (n = 69) of nonhydropic fetuses survival. Hydropic fetuses showed higher hematocrit drop off than nonhydropic ones (P < 0.01). Compared to the interval between the first and second IUT, the daily fetal Hct decline was lower after the third one (P < 0.05). Stratifying by the presence of hydrops, nonhydropic fetuses showed a smaller decrease at the third and fourth intervals (P < 0.01 and P < 0.05, respectively). Among hydropic fetuses, there is a trend of smaller Hct decrease along successive IUTs (interval 3, P = 0.08; interval 4, P = 0.07; and interval 5, P = 0.10).

Following some IUTs, fetal hematocrit decrease is lower and larger intervals between the transfusions could be accomplished. Multicenter studies should investigate an algorithm for timing subsequent IUTs, considering Doppler values, estimated fetal hematocrit decline and other parameters.