title: A prospective study on the prevalence and risk factors for neonatal thrombocytopenia and platelet alloimmunization among 9332 unselected Brazilian newborns.
abstract: BACKGROUND
  Neonatal thrombocytopenia (NT) occurs in 0.5 to 0.9% of unselected Caucasian newborns. However, the prevalence of this complication in other populations is unknown. In this study the prevalence/causes of NT was determined in Brazilian newborns, a population characterized by admixture among Indigenous, Africans, and Caucasians.
  
  
  METHODS
  A prospective study was carried out in a 3-year period, to determine the prevalence and causes of thrombocytopenia in cord blood samples. Genotyping for HPA 1-5 systems was performed in pairs of mother/neonates with and without thrombocytopenia. All mothers with genotypic mismatches from each group were tested for HPA-specific antibody using the MAIPA technique to identify alloimmunization.
  
  
  RESULTS
  Platelet counts <100 x 10(9)/L were detected in 1.5% of 9,332 unselected newborns. In 0.15%, platelet count was <50 x 10(9)/L. Clinically significant bleeding was rare. Underlying diseases were present in 48% of the thrombocytopenic cases. HPA 1-5 system genotype mismatches occurred in 50% of gestations, but did not predict the risk for thrombocytopenia. Notably, mismatched genotypes for HPA-5 were slightly increased in the thrombocytopenic group. The presence of anti-HPA-5b antibodies was observed in 0.05% of unselected pregnancies, but increased to 12% among mothers of neonates with thrombocytopenia and mismatched genotype (N = 51).
  
  
  CONCLUSIONS
  Neonatal thrombocytopenia is common among Brazilian newborns at rates comparable with those described among Caucasians. These data suggest that screening for genotypic HPA mismatch, followed by an HPA-specific immunoassay system, particularly for the HPA-5 system, among mothers of newborns with thrombocytopenia in our population would allow the identification of pregnancies at risk of alloimmune thrombocytopenia.
authors.affiliation: Hematology and Transfusion Center, the Department of Neonatology, State University of Campinas, UNICAMP, Campinas-SP, Brazil. vagner@unicamp.br
authors.forename: Vagner
authors.initials: V
authors.lastname: Castro
authors.forename: Hartmut
authors.initials: H
authors.lastname: Kroll
authors.forename: Andréa F
authors.initials: AF
authors.lastname: Origa
authors.forename: Mônica A
authors.initials: MA
authors.lastname: Falconi
authors.forename: Sílvia B D
authors.initials: SB
authors.lastname: Marques
authors.forename: Sérgio T
authors.initials: ST
authors.lastname: Marba
authors.forename: Renato
authors.initials: R
authors.lastname: Passini
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Annichino-Bizzacchi
authors.forename: Fernando F
authors.initials: FF
authors.lastname: Costa
authors.forename: Sentot
authors.initials: S
authors.lastname: Santoso
authors.forename: Valder R
authors.initials: VR
authors.lastname: Arruda
mesh_terms: D000293:Adolescent; D000328:Adult; D000906:Antibodies / Q000097:blood; D016824:Antigens, Human Platelet / Q000235:genetics; D001792:Blood Platelets / Q000276:immunology* / Q000473:pathology; D001938:Brazil / Q000453:epidemiology; D005260:Female; D005838:Genotype; D006680:HLA Antigens / Q000276:immunology; D006801:Humans; D007231:Infant, Newborn; D007518:Isoantibodies / Q000097:blood*; D008875:Middle Aged; D009035:Mothers; D010976:Platelet Count; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D013921:Thrombocytopenia / Q000097:blood / Q000151:congenital / Q000453:epidemiology* / Q000276:immunology*
chemical_list: D000906:Antibodies; D016824:Antigens, Human Platelet; D006680:HLA Antigens; D007518:Isoantibodies