title: Noninvasive determination of fetal rh blood group, D antigen status by cell-free DNA analysis in maternal plasma: experience in a Brazilian population.
abstract: We evaluated the diagnostic accuracy of Rh blood group, D antigen (RHD) fetal genotyping, using real-time polymerase chain reaction in maternal blood samples, in a racially mixed population. We performed a prospective study conducted between January 2006 and December 2007, analyzing fetal RHD genotype in the plasma of 102 D- pregnant women by real-time polymerase chain reaction, targeting exons 7 and 10 of the RHD gene. Genotype results were compared with cord blood phenotype obtained after delivery or before the first intrauterine transfusion when necessary. Most of the participants (75.5%) were under 28 weeks of pregnancy, and 87.5% had at least one relative of black ancestry. By combining amplification of two exons, the accuracy of genotyping was 98%, sensitivity was 100%, and specificity was 92%. The positive likelihood ratio was 12.5, and the negative likelihood ratio was 0. The two false-positive cases were confirmed to be pseudogene RHD by real-time polymerase chain reaction. There were no differences between the patients with positive or negative Coombs test ( P = 0.479). Determination of fetal RHD status in maternal peripheral blood was highly sensitive in this racially mixed population and was not influenced by the presence of antierythrocyte antibodies.
authors.affiliation: Department of Obstetrics, Federal University of São Paulo (UNIFESP), São Paulo, SP Brazil.
authors.forename: Paulo Alexandre
authors.initials: PA
authors.lastname: Chinen
authors.forename: Luciano Marcondes Machado
authors.initials: LM
authors.lastname: Nardozza
authors.forename: Ciro Dresch
authors.initials: CD
authors.lastname: Martinhago
authors.forename: Luiz
authors.initials: L
authors.lastname: Camano
authors.forename: Silvia
authors.initials: S
authors.lastname: Daher
authors.forename: David Baptista da Silva
authors.initials: DB
authors.lastname: Pares
authors.forename: Thais
authors.initials: T
authors.lastname: Minett
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Antonio Fernandes
authors.initials: AF
authors.lastname: Moron
mesh_terms: D001938:Brazil; D004247:DNA / Q000097:blood* / Q000302:isolation & purification; D005260:Female; D005312:Fetal Blood / Q000276:immunology; D005838:Genotype; D006801:Humans; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D044469:Racial Groups / Q000235:genetics*; D012204:Rh-Hr Blood-Group System / Q000097:blood / Q000235:genetics*; D012680:Sensitivity and Specificity
chemical_list: D012204:Rh-Hr Blood-Group System; D004247:DNA