Non-invasive prenatal determination of fetal RhD genotyping from maternal plasma: a preliminary study in Pakistan.
OBJECTIVE
To determine the accuracy of the non-invasive pre-natal real-time polymerase chain reaction based fetal RhD genotyping from maternal plasma.


METHODS
Cross-sectional study.


METHODS
Juma Health Sciences Research Laboratory, The Aga Khan University Hospital, Karachi, from July to December 2008.


METHODS
Cell-free plasma DNA from 21 D-negative women with D-positive spouse between 20-39 weeks of gestation was tested for the presence of exon 5 region of RhD gene using real-time polymerase chain reaction. b-globin was employed as the house-keeping gene. Sensitivity and specificity of the real-time PCR-based non-invasive fetal RhD genotyping was obtained by calculating proportion of the D-positive fetuses that were D-positive at birth as well.


RESULTS
Of the 21 D-negative women 13 and 8 neonates were determined to be D-positive and D-negative, respectively, by serologic studies on cord blood samples at birth. RhD status was correctly determined in 17 of 21 cases. There were three false-positive and one false-negative results. The sensitivity and specificity of the assay was 92.3% (95% CI: 62.1, 99.6) and 62.5% (95% CI: 25.9, 89.8), respectively. The positive and negative predictive value of the assay was 80% (95% CI: 51.4, 94.7) and 83.3% (36.5, 99.1), respectively.


CONCLUSIONS
These preliminary results demonstrate the feasibility of non-invasive pre-natal diagnosis of fetal RhD status of D-negative mothers in Pakistan.
Mohammed
Nuruddin
N
Department of Obstetrics and Gynaecology, The Aga Khan University Hospital, Karachi. nuruddin.badruddin@aku.edu
Kakal
Fatima
F
Somani
Mehreen
M
Zafar
Wajiha
W
D001788:Blood Grouping and Crossmatching / Q000379:methods*; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D008431:Maternal-Fetal Exchange / Q000235:genetics; D010865:Pilot Projects; D016133:Polymerase Chain Reaction / Q000592:standards; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012203:Rh Isoimmunization / Q000097:blood / Q000235:genetics / Q000517:prevention & control*; D012204:Rh-Hr Blood-Group System / Q000097:blood* / Q000145:classification / Q000235:genetics; D012680:Sensitivity and Specificity
D012204:Rh-Hr Blood-Group System