Evaluation of non-invasive prenatal RHD genotyping of the fetus.
OBJECTIVE
To evaluate a non-invasive molecular test using free circulating fetal DNA in maternal plasma to predict the fetal RHD type.


METHODS
A prospective cohort study.


METHODS
Venous blood samples were collected from 140 Rhesus (Rh) D-negative women booked for antenatal care in two tertiary maternity hospitals in Sydney and Brisbane between November 2006 and April 2008. Cell-free DNA, including free maternal and fetal DNA, was extracted from maternal plasma in the tertiary Australian Red Cross Blood Service laboratory, and three exon regions of the RHD gene were amplified.


METHODS
Comparison of the predicted fetal RHD status and the infant's RhD serotype. Secondary analysis involved using SRY and RASSF1A assays as internal controls to confirm the presence of fetal DNA in RHD-negative samples.


RESULTS
Of 140 samples tested, results for RHD status were assigned for 135, and all 135 predictions were correct. A result was not assigned in five cases: three did not meet strict threshold criteria for classification, and two were due to RHD variants. Fetal SRY status was correctly predicted in 137 of 140 cases. In 16 samples typed both RHD- and SRY-negative, a positive RASSF1A result verified the presence of fetal DNA.


CONCLUSIONS
Non-invasive testing of multiple exons provides a robust method of assessing fetal RHD status, and provides a safer alternative to amniocentesis for the management of RhD-negative pregnant women who are isoimmunised.
Hyland
Catherine A
CA
Research and Business Development, Australian Red Cross Blood Service, Brisbane, QLD, Australia. chyland@arcbs.redcross.org.au
Gardener
Glenn J
GJ
Davies
Helen
H
Ahvenainen
Minna
M
Flower
Robert L
RL
Irwin
Darryl
D
Morris
Jonathan M
JM
Ward
Christopher M
CM
Hyett
Jonathan A
JA
D000328:Adult; D015331:Cohort Studies; D004247:DNA / Q000097:blood*; D005091:Exons / Q000235:genetics; D005260:Female; D005315:Fetal Diseases / Q000097:blood / Q000235:genetics*; D005838:Genotype; D006801:Humans; D008431:Maternal-Fetal Exchange / Q000235:genetics*; D011247:Pregnancy; D011295:Prenatal Care / Q000379:methods; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D011785:Quality Assurance, Health Care / Q000458:organization & administration; D011793:Queensland; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012204:Rh-Hr Blood-Group System / Q000097:blood / Q000235:genetics*; D012680:Sensitivity and Specificity; D055815:Young Adult
D012204:Rh-Hr Blood-Group System; C026410:Rho(D) antigen; D004247:DNA