Clinical experience with the screening of fetal aneuploidies in twins using SNP-based noninvasive prenatal testing

Twins account for approximately 1 in 30 live births in the United States. Clinical experience studies focusing on noninvasive prenatal testing (NIPT) for detecting aneuploidies in twins are limited. This study reports the performance of a single nucleotide polymorphism (SNP)-based NIPT in the largest cohort with known outcomes for high-risk twin aneuploidy results. This is a retrospective analysis of 18,984 results from commercial SNP-based NIPT tests performed in twins between October 2, 2017, and December 31, 2019. Follow-up for all 211 high-risk cases was solicited (Figure 1). Follow-up outcomes were obtained in 105 cases. Positive predictive values (PPVs) for high-risk results were 88.7% for trisomy 21 and 72.7% for trisomy 18. The results were stratified into monozygotic (MZ) and dizygotic (DZ). The PPVs in MZ were 100% for both trisomy 21 and trisomy 18. No trisomy 13 cases were detected in the MZ group. The PPVs in DZ were 88.1%, 70.0%, and 66.7% for trisomy 21, trisomy 18, and trisomy 13, respectively. The performance of SNP-based NIPT in this large twin cohort was comparable to previously reported twin NIPT studies. SNP-based NIPT allows for zygosity-based PPV assessment.