Fetal platelet counts correlate with the severity of the anemia in red-cell alloimmunization

Objective: To determine whether fetal anemia secondary to maternal red-cell alloimmunization is associated with thrombocytopenia. Methods: The records of 78 patients undergoing intrauterine transfusion for red-cell alloimmunization were reviewed. Pre-transfusion fetal platelet counts were compared between hydropic and nonhydropic fetuses. A regression analysis was performed between the fetal platelet counts and the fetal bilirubin levels, hematocrits, and reticulocyte counts taken at the initial transfusion. The hematocrits, reticulocyte counts, and bilirubin levels were adjusted for gestational age by calculating the number of standard deviations (SDs) from the mean for that age or the multiples of the mean (MOM). Student t test, Pearson coefficient, and contingency table randomization test were used to analyze the data. P < .05 was considered significant. Results: Thirty-seven fetuses were hydropic and 41 were nonhydropic. Hydropic fetuses had a significantly lower platelet count than nonhydropic fetuses (197.5 ± 86.4 versus 252.6 ± 73.7 × 10³/μL; P < .01). Platelet counts correlated negatively with the reticulocyte count MOM (r = –0.652; P < .01) and the hematocrit SDs below the mean (r = –0.659; P <.01), but did not correlate with the bilirubin MOM (r = –0.183; P = .2). Conclusions: Hydropic and severely anemic fetuses are at increased risk for thrombocytopenia. We suggest that increased erythropoiesis diverts the hematopoietic stem cell away from thrombopoiesis.