Thrombocytopenia, defined as a platelet count < 150,000/mm3, is a very common hematologic problem in the neonatal period. Multiple etiologies are known to be associated with thrombocytopenia in neonates. Thrombopoietin (TPO) is known to be the central regulator of megakaryocyte and platelet production in adults and infants. However, the role of TPO in neonatal platelet regulation is not well understood. TPO levels have been shown to be higher in neonates with thrombocytopenia, with a decrease in TPO after resolution of the thrombocytopenia. The response of TPO levels in neonates after platelet transfusion has never been studied. In addition, the optimal volume of platelet transfusions has never been studied in neonates. This study will evaluate the response to 2 different volumes of platelet transfusion.