Niet-invasieve prenatale test bij meerlingzwangerschappen: een retrospectieve analyse van de distributie van de foetale fractie

Abstract

Noninvasive prenatal testing in multiple pregnancies: retrospective analysis of the fetal fraction distribution This article describes the distribution of the fetal fraction (FF) in noninvasive prenatal testing (NIPT) in multiple pregnancies. A retrospective study of 514 NIPT experiments was performed in 484 women with an (originally) multiple pregnancy from January 1st, 2017 to December 31st, 2019 at the Center for medical genetics in Ghent (Belgium). The FF distribution in vanishing twin, twin and triplet pregnancies was significantly different with a mean of 14%, 18.1% and 23.7% respectively. Test failure due to a low FF was higher in dichorionic-diamniotic (DCDA) twins (9.5%) compared to monochorionic-diamniotic (MCDA) twins (0%). The mean ratio FF based on the Y-chromosome (FFY)/total fetal fraction in male-male pregnancies was 0.96, in male-female pregnancies 0.43 and in female-female pregnancies 0.0. In vanishing twin pregnancies, the duration of persistence of cell-free fetal DNA (cffDNA) from the demised cotwin was up to 7 weeks. Test failure due to a low FF seems to appear more frequently in DCDA twins compared to MCDA twins, which could be explained by the higher FF threshold in DCDA twins (8%) in comparison to MCDA twins (4%). In mixed pregnancies, on average each fetus seems to contribute equally to the FF, although this does not seem to apply to all mixed pregnancies, giving rise to the possibility of an unequal contribution and a higher risk of a false negative result.