This is a prospective observational study designed to evaluate Immature Platelet Fraction or Immature Platelet Count and Platelet Function Analyzer-100/200 Closure Time-ADP (in vitro bleeding time) as markers of bleeding risk in thrombocytopenic preterm neonates admitted to the Neonatal Intensive Care Unit.

Thrombocytopenia is a known risk factor for clinically significant bleeding in neonates. However, there is a poor correlation between degree of thrombocytopenia and bleeding risk. A better marker of bleeding risk suitable for use in neonates could help physicians more accurately determine the risk/benefit ratio of platelet transfusions, guiding platelet transfusion decisions, and potentially protecting vulnerable infants from exposure to unnecessary transfusion-related risks. The investigators recently found that the Platelet Function Analyzer (PFA) Closure Time-Collagen/ADP (CT-ADP) was a better marker of bleeding than the platelet count in preterm neonates. However, the CT-ADP requires 0.8 mL blood limiting its potential widespread use. The Immature Platelet Fraction (IPF) is a new laboratory marker measuring the % newly released and more active platelets, measured from the same sample as the platelet count. This is a prospective observational study designed to evaluate IPF as marker of bleeding risk in thrombocytopenic neonates admitted to the Neonatal Intensive Care Unit, compared to platelet counts alone. And also, to validate the previously found association between PFA-100/200 CT-ADP and bleeding in a bigger cohort, to compare the IPF with the PFA-100/200 CT-ADP as bleeding predictors and to assess whether the PFA-100/200 CT-ADP combined with the IPF is able to predict bleeding in thrombocytopenic preterm neonates.

Inclusion Criteria:

• Have a gestational age <32 weeks and a birth weight ≥500 grams;
• Have a platelet count <100 x 109/L; and
• Have a parent/guardian willing to provide written informed consent.

Exclusion Criteria:

• Are not expected to survive for >24 hours by the Attending Neonatologist;
• Are thought to have a familial thrombocytopenia or platelet dysfunction, based on family history or clinical presentation (associated congenital malformations, platelet morphology).

- Infants will be eligible for study if they have a gestational age <32 weeks and a birth weight ≥500 grams; and have a platelet count <100 x 109/L.