Newly released platelets, referred to as immature platelets, can be reliably quantified based on their RNA content by flow cytometry in an automated blood analyser. The absolute number of immature platelets (IPF#) and the immature platelet fraction (IPF%) reflect megakaryopoietic activity. We aimed to analyse the implication of these parameters in analysing the pathomechanism of early-onset neonatal thrombocytopenia. Platelet counts and IPF were determined at day 1 to 3 (d1 to d3) in 857 neonates admitted to intensive care. In thrombocytopenic patients (platelet counts