This is a prospective longitudinal study that evaluates Platelet Function Analyzer-100 (PFA-100) CT-ADPs (closure time-ADP) and incidence of bleeding using the Neonatal Bleeding Assessment Tool - Neo-BAT in preterm neonates <32 weeks gestational age or with a birth weight <1500 grams and with different degrees of thrombocytopenia.

The investigators hypothesized that PFA-100 CT-ADP, a global in vitro test of primary hemostasis, will be a better predictor of clinical bleeding in neonates than platelet count alone. A bleeding risk assessment marker could help physicians more accurately determine the risk/benefit ratio of platelet transfusions, guiding platelet transfusion decisions in neonates with thrombocytopenia.

Inclusion Criteria:

• <32 weeks gestation or with a birth weight <1500 grams;
• Have confirmed moderate-to-severe thrombocytopenia, defined as a platelet count <100x109/L;
• Have a parent/guardian willing to comply with the protocol and provide written informed consent.

Exclusion Criteria:

• Are not expected to survive by the Attending Neonatologist;
• Are thought to have a congenital thrombocytopenia or platelet dysfunction, based on family history or clinical presentation (e.g. associated congenital malformations, platelet morphology);
• Have a major chromosomal anomaly such as Trisomy 13, 18, or 21.

Patients admitted to the Neonatal Intensive Care Unit who are <32 weeks gestation or with a birth weight <1500 grams.