Background: A fault in chromosome distribution during cell division leads to aneuploidy, which can be associated with thrombocytopenia. Various hematological abnormalities have been reported among neonates with Down syndrome (DS). Neutrophilia, thrombocytopenia and polycythemia were the most common hematological abnormalities observed among neonates with Down syndrome. In particular, thrombocytopenia below 150×109/L was found approximately in two-third of DS and 6% of counts below 50,000 was detected during the first week of life.The exact mechanism remains unknown, but is thought to be due to decreased platelet production from chronic fetal hypoxia. fetal hypoxia also leads to intrauterine growth retardation and suboptimal response of thrombopoitin system (TPO) to thrombocytopenia in DS during the neonatal period. Few cases of alloimmune thrombocytopenia with DS due to anti-HPA antibody were reported.Methods: Data from multihospital healthcare systems shows large two case series of infants with cytogenetically confirmed DS and a reference group infants without birth defects all born during the period 2009-2015. During this period, 145,522 live births were recorded at 18 hospitals. Down syndrome was recognized in 226 newborn (1 in 644). Data were analyzed using multivariate logistic regression analysis expressed as adjusted odds ratio (aORs) with 95% confidence intervals (95% CIs).Results & Conclusion: Infants with DS had a significantly higher risk for thrombocytopenia (aOR = 32.4). Platelet counts in DS averaged 104600 per microliter. The mean platelet volume did not correlate with the platelet count, but tended to run slightly large (9.2 +/- 1.3 fl). Persistence of thrombocytopenia beyond 8 to 12 weeks after birth should warrant a hematology consult. Thrombocytopenia can be seen associated with some types of congenital heart defects. Karyotype testing should be done in all obviously dysmorphic infants with thrombocytopenia. It seems reasonable to recommend that one or more CBCs be obtained on all neonates with Down syndrome
