Analysis of false‐positive results of fetal RHD typing in a national screening program reveals vanishing twins as potential cause for discrepancy. (19th May 2015)

• Record Type: Journal Article
• Authors: Thurik, F. F.; Ait Soussan, A.; Bossers, B.; Woortmeijer, H.; Veldhuisen, B.; Page‐Christiaens, G. C. M. L.; de Haas, M.; van der Schoot, C. E.
• Is Part Of: Prenatal diagnosis. Volume 35:Number 8(2015:Aug.)
• Page Start: 754
• Page End: 760
• Publication Date: 2015-05-19
• Subjects: Prenatal diagnosis -- Periodicals; Fetus -- Diseases -- Diagnosis -- Periodicals; Electronic journals; 618.32075
• DOI: 10.1002/pd.4600
• Languages: English
• ISSNs: 0197-3851

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <sec id="pd4600-sec-0001" sec-type="section"> <title>Objectives</title> <p>We aim to elucidate causes of false‐positive fetal <italic>RHD</italic> screening results obtained with cell‐free DNA.</p> </sec> <sec id="pd4600-sec-0002" sec-type="section"> <title>Methods</title> <p>Fetal <italic>RHD</italic> screening was performed in 32 222 samples from RhD‐negative women by multiplex real‐time PCR in triplicate for <italic>RHD</italic> exons 5 and 7 using cell‐free DNA isolated from maternal plasma obtained in the 27th gestational week. PCR results were compared with cord blood serology in 25 789 pregnancies (80.04%). False‐positive cases were analyzed. Known biological causes (<italic>RHD</italic> variant genes), technical causes of discordance, and errors around blood sampling were investigated with leukocyte DNA from maternal and cord blood, and cell‐free DNA from stored maternal plasma.</p> </sec> <sec id="pd4600-sec-0003" sec-type="section"> <title>Results</title> <p>Not only <italic>RHD</italic> but also Y‐chromosome (DYS14) sequences were present in four plasma samples from <italic>RHD</italic>‐negative women bearing an <italic>RHD</italic>‐negative girl. Sample mix‐up and other sampling errors could be excluded in three samples.</p> </sec> <sec id="pd4600-sec-0004" sec-type="section"> <title>Conclusions</title> <p>These results indicate that false‐positive fetal <italic>RHD</italic> screening results can be caused by cell‐free DNA fragments in maternal plasma derived from a third cell line that is not representative for either the maternal genome or the genome of the vital fetus. We propose that remaining (cyto)trophoblasts of a vanishing twin are the underlying mechanism, and we estimate a frequency of this phenomenon of 0.6%. © 2015 John Wiley & Sons, Ltd.</p> </sec> </abstract>