Although thrombocytopenia is relatively rare in the general newborn population, it occurs more frequently in patients admitted to neonatal intensive care units. The two main underlying pathologic mechanisms are increased destruction or decreased production. Severe neonatal thrombocytopenia (platelet count <50,000/microL) is associated with bleeding and, potentially, significant morbidity. As a result, it is important to identify at-risk infants, and if needed, initiate therapy to prevent associated complications.
The incidence and causes of thrombocytopenia in the newborn are reviewed here. The evaluation and general management of neonatal thrombocytopenia are discussed separately. (See "Clinical manifestations, evaluation, and management of neonatal thrombocytopenia".)
DEFINITIONS AND INCIDENCE
Neonatal thrombocytopenia is typically defined as a platelet count less than 150,000/microL based upon the definition used in adults, which corresponds to values at or below the 5th percentile. Degrees of thrombocytopenia can be further subdivided into mild (platelet count 100,000 to 150,000/microL), moderate (50,000 to 99,000/microL), and severe (<50,000/microL).
However, healthy preterm and term newborns can have platelet counts below the defined normal platelet count [1-3].This was best illustrated in a study from the Intermountain Healthcare group that reviewed the platelet counts of 34,146 neonates (gestational age from 22 to 42 weeks) during the first three days of life . In neonates, the 5th percentile was lower than the standard adult value of 150,000/microL and decreased with decreasing gestational age. For example, the 5th percentile was 104,200/microL for infants below 32 weeks gestation, and was 123,100/microL for late preterm (34 to 36 weeks gestation) and term (gestational age greater than 37 weeks) infants. Platelet counts increased with advancing postnatal age.
Severe thrombocytopenia — Severe thrombocytopenia (defined as a platelet count <50,000/microL) and/or persistent thrombocytopenia can result in bleeding. Severe neonatal thrombocytopenia is uncommon in the general healthy newborn population, with a reported incidence between 0.14 and 0.24 percent [4,5].