Noninvasive determination of fetal rh blood group, D antigen status by cell-free DNA analysis in maternal plasma: experience in a Brazilian population.
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.
Chinen
Paulo Alexandre
PA
Department of Obstetrics, Federal University of São Paulo (UNIFESP), São Paulo, SP Brazil.
Nardozza
Luciano Marcondes Machado
LM
Martinhago
Ciro Dresch
CD
Camano
Luiz
L
Daher
Silvia
S
Pares
David Baptista da Silva
DB
Minett
Thais
T
Araujo Júnior
Edward
E
Moron
Antonio Fernandes
AF
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
D012204:Rh-Hr Blood-Group System; D004247:DNA