Detection of triploid, molar, and vanishing twin pregnancies by a single-nucleotide polymorphism–based noninvasive prenatal test

TLDR

Vanishing twins are often aneuploid and residual cfDNA can bias NIPT, so detecting additional fetal haplotypes should reduce false positives and incorrect sex calls. The study aimed to evaluate SNP‑based NIPT’s ability to detect triploid, unrecognized twin, and vanishing twin pregnancies. Maternal plasma cfDNA was isolated, amplified with a 19,488‑plex PCR, sequenced, and analyzed for fetal chromosome copy number and extra haplotypes. In 0.42% of 30,795 cases, additional fetal haplotypes were detected, and among 76 confirmed cases, 42.1% were vanishing twins, 48.7% viable twins, 5.3% diandric triploids, and 3.9% nontriploid without co‑twin demise; all five vanishing twin losses occurred in the first trimester, with up to 8 weeks between loss and NIPT detection, demonstrating that SNP‑based NIPT can identify vanished twin, previously unrecognized twin, and triploid pregnancies.

Abstract

We sought to determine the ability of single-nucleotide polymorphism-based noninvasive prenatal testing (NIPT) to identify triploid, unrecognized twin, and vanishing twin pregnancies.The study included 30,795 consecutive reported clinical cases received for NIPT for fetal whole-chromosome aneuploidies; known multiple gestations were excluded. Cell-free DNA was isolated from maternal blood samples, amplified via 19,488-plex polymerase chain reaction, and sequenced. Sequencing results were analyzed to determine fetal chromosome copy number and to identify the presence of additional fetal haplotypes.Additional fetal haplotypes, indicative of fetal triploidy, vanishing twin, or undetected twin pregnancy, were identified in 130 (0.42%) cases. Clinical confirmation (karyotype for singleton pregnancies, ultrasound for multifetal pregnancies) was available for 58.5% (76/130) of cases. Of the 76 cases with confirmation, 42.1% were vanishing twin, 48.7% were viable twin, 5.3% were diandric triploids, and 3.9% were nontriploid pregnancies that lacked evidence of co-twin demise. One pregnancy had other indications suggesting triploidy but lacked karyotype confirmation. Of the 5 vanishing twin cases with a known date of demise, 100% of losses occurred in the first trimester; up to 8 weeks elapsed between loss and detection by NIPT.This single-nucleotide polymorphism-based NIPT successfully identified vanished twin, previously unrecognized twin, and triploid pregnancies. As vanishing twins are more likely to be aneuploid, and undetected residual cell-free DNA could bias NIPT results, the ability of this method to identify additional fetal haplotypes is expected to result in fewer false-positive calls and prevent incorrect fetal sex calls.