Unexpectedly, the mice displayed only a mild defect in erythropoiesis but a severe impairment of megakaryopoiesis, resulting in severe thrombocytopenia with a near complete absence of normal platelets, and an associated IUGR.15 The IUGR in p45 NF-E2-deficient embryos is independent of thrombocytopenia and detailed mechanistic studies revealed a new function of p45 NF-E2 in trophoblast cell differentiation.16, 17 In the absence of p45 NF-E2 enhanced GCM1 activity and syncytiotrophoblast formation impairs placental vascularization and embryonic growth in mice. Here, GCM1 is linked to fetal growth restriction.