Platelets are seen under microscope as small anucleated fragments of megakaryocytes that circulate in the blood as discs with an average volume of about 7.5 fimtolitre , 14 times smaller than erythrocytes. Platelets count in premature infant is slightly lower than that of healthy term infant but is still within the normal range (150,000 to 450,000 unit/ litre ).~The most common risk factors for thrombocytopenia are~Sepsis: Thrombocytopenia is a frequent problem in neonatal sepsis and is among the most predictive, independent risk factors for sepsis-associated mortality~Low birth weight: It is recorded that thrombocytopenia was more common among the smallest patients; 85% incidence among those ⩽800 gram, 60% among those 801 to 900 gram, and 53% among those 901 to 1000 gram~Perinatal asphyxia: Thrombocytopenia occurred in 31% of neonates with asphyxia versus 5% of matched non asphyxiated controls admitted to a neonatal intensive care unit~Prematurity: In a normal pregnancy, the fetal platelet count reaches adult levels (150-450 × 106/ millilitre) by the second trimester of pregnancy. Thrombocytopenia , defined as less than 150,000/ millilitre, occurs in 18 to 40% of all preterm neonates (gestational age <37 weeks) admitted to neonatal intensive care units
Thrombocytopenia is diagnosed when platelet count is lower than 150,000 U/L, it is a common hemostatic problem in neonatal intensive care units According to platelets count, it is classified into mild thrombocytopenia with platelet count 100,000 to 150,000 U/L, moderate thrombocytopenia with platelet count 50,000 to 100,000 U/L and severe thrombocytopenia that have platelet count less than or equal to 50,000 U/L.