Infants who have low platelets and who require a platelet transfusion are included in this study. Platelet transfusions are routinely given to infants when their platelet count falls below a certain level. The study will look at the amount of platelets transfused. The purpose of the study is to evaluate the effect of platelet transfusions on the level of a protein (thrombopoietin) which is known to help control platelet production.

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.

We hypothesize that a decrease in plasma TPO levels will be seen following a platelet transfusion in a population of neonates with thrombocytopenia. We also hypothesize that a platelet transfusion of 15 mL/kg will result in a greater rise in platelet count than a transfusion pf 10 mL/kg of platelets.

Inclusion Criteria:

• Preterm infants with thrombocytopenia
• Decision made by medical team to transfuse with platelets

Exclusion Criteria:

• Infants with major congenital malformations

Infants who require platelet transfusion