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Circulating Cell-Free DNA to Determine the Fetal RHD Status in All Three Trimesters of Pregnancy
Kenneth J Moise1, Manisha Gandhi, Noemi H Boring
1Departments of Obstetrics and Gynecology at the Baylor College of Medicine, Houston, Texas; The Ohio State University Wexner Medical Center, Columbus, Ohio; Columbia University Medical Center, New York, New York; the University of North Carolina School of Medicine, Chapel Hill, North Carolina; Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania; Tristate Maternal Fetal Medicine Association, Inc, Cincinnati, Ohio; and the Department of Obstetrics, Gynecology and Reproductive Sciences, Icahn School of Medicine at Mt. Sinai, New York, New York; the Departments of Obstetrics and Gynecology at Wayne State University/Detroit Medical Center, Detroit, Michigan; New York Presbyterian Queens and Weill Cornell Medical College, New York, New York; Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; Evergreen Hospital, Seattle, Washington; Phoenix Perinatal Associates, Phoenix, Arizona; McGill University, Montréal, Quebec, Canada; the University of British Columbia, Vancouver, Canada; Medical University of South Carolina, Charleston, South Carolina; Spectrum Health Hospitals, Grand Rapids, Michigan; William Beaumont Hospital, Royal Oak, Michigan; Drexel University College of Medicine, Philadelphia, Pennsylvania; and Sequenom, Inc, and the Sequenom Center for Molecular Medicine, San Diego, California.
Objective:
To estimate the accuracy of a new assay to determine the fetal RHD status using circulating cell-free DNA.
Methods:
This was a prospective, observational study. Maternal blood samples were collected in each trimester of pregnancy in 520 nonalloimmunized RhD-negative patients. Plasma samples were analyzed for circulating cell-free DNA using the SensiGENE RHD test, which used primers for exons 4 and 7 as previously described and incorporated a new primer design for exon 5 of the RHD gene. Neonatal serology for RhD typing using cord blood at birth was undertaken and results were stored in a separate clinical database. After unblinding the data, results of the DNA analysis were compared with the neonatal serology.
Results:
Inconclusive results secondary to the presence of the RHD pseudogene or an RHD variant were noted in 5.6%, 5.7%, and 6.1% of the first-, second-, and third-trimester samples, respectively. The incidence of false-positive rates for RhD (an RhD-negative fetus with an RHD-positive result) was 1.54% (95% confidence interval [CI] 0.42-5.44%), 1.53% (CI 0.42-5.40%), and 0.82% (CI 0.04-4.50%), respectively. There was only one false-negative diagnosis (an RhD-positive fetus with an RHD-negative result), which occurred in the first trimester (0.32%; 95% CI 0.08-1.78%). Genotyping for mismatches across repeated samples revealed that this error was related to mislabeling of samples from two patients collected on the same day at one of the collection sites. Overall test results were in agreement across all three trimesters (P>.99).
Conclusion:
Circulating cell-free DNA can accurately predict the fetal RhD status in all three trimesters of pregnancy.
