Intrauterine transfusions influence fetal leukocyte counts and subsets

The objective of this study was to determine the effect of intravascular intrauterine transfusion (IUT) on fetal leukocyte counts and subsets. For this purpose, pre- and post-transfusion blood samples of 81 fetuses, receiving a total of 253 IUTs, were compared. Immediately after the IUT procedure an average decrease in fetal leukocyte count of 4 per cent was observed. When corrected for the dilutional effect of IUT, the average increase in leukocyte count was 41 per cent (n = 180), indicating that IUT resulted in a relative leukocytosis. This was in contrast to the statistically significant average decrease in platelet count of 62 per cent (P < 0.0001) immediately after IUT, suggesting that the relative increase in leukocyte count was lineage-specific. Differential leukocyte counts revealed that the changes in fetal leukocyte count, in terms of percentage, after IUT were the results of an increase in monocytes and basophils and a decrease in lymphocytes. Flow cytometric analysis demonstrated that the decrease in lymphocytes was evenly distributed among the different subpopulations and not the result of a specific down-regulation of one or more lymphocyte subsets. We observed only a modest relation between the duration of the transfusion and the degree of relative leukocytosis, suggesting that the onset of the leukocytosis probably occurred within minutes after the start of the transfusion. The observed effects appeared transient since the pre-transfusion leukocyte count between each consecutive IUT did not reveal significant alterations during the course of IUT treatment.