Infants of diabetic mothers (IDMs) have hematologic indices consistent with increased fetal erythropoiesis, presumably in response to chronic intrauterine hypoxemia. We hypothesized that increased erythropoiesis, as is evident from increased nucleated erythrocyte counts, would be accompanied by interrelated changes in thrombopoiesis and would correlate with maternal glycemic control during pregnancy. We compared absolute nucleated erythrocyte counts and platelet counts obtained in the first 24 hours of life in 32 term, nonasphyxiated IDMs with 47 controls. The IDM group had higher absolute nucleated erythrocyte counts (1.0 +/- 1.3 x 10(9)/L versus 0.4 +/- 0.7 x 10(9)/L; p < 0.05), and lower platelet counts (235 +/- 77 x 10(9)/L versus 348 +/- 79 x 10(9)/L; p < 0.001) than controls. Absolute nucleated erythrocyte counts correlated inversely with platelet counts (r = -0.28; p < 0.02). These neonatal hematologic measurements did not correlate with various parameters of maternal glycemic control. We conclude that in IDMs, increased erythropoiesis is accompanied by decreased platelet counts. These data are consistent with the theory of an erythropoietin-induced shift of fetal multipotent stem cell differentiation toward erythropoiesis at the expense of thrombopoiesis.