Comment on: “Performance of Noninvasive Prenatal Testing in Vanishing-twin and Multiple Pregnancies: Results of TRIDENT-2 Study”

Noninvasive prenatal testing (NIPT) analyzes cell-free DNA (cfDNA) in maternal blood and is widely used in singleton pregnancies to screen for fetal chromosomal abnormalities. In vanishing-twin pregnancies, in which one fetus in a multiple gestation undergoes a demise during the first trimester, interpretation is more complex because cfDNA from the deceased twin can remain in maternal circulation and produce false positive results. Although NIPT performance for trisomy 21 in singleton pregnancies is well established and has been evaluated in vanishing-twin pregnancies, data on its accuracy for trisomies 18 and 13 and other chromosomal abnormalities remain limited. This study evaluated the performance of NIPT in vanishing-twin and multiple pregnancies. This prospective observational study was conducted within the TRIDENT-2 nationwide implementation study of NIPT in the Dutch prenatal screening program. The analysis included monochorionic and dichorionic twin pregnancies, multiple pregnancies, and vanishing-twin pregnancies between 2020 and 2023. Pregnant individuals could elect testing limited to trisomies 21, 18, and 13 or expanded screening for additional large chromosomal abnormalities. Maternal blood samples were collected after 11 weeks’ gestation and analyzed at clinical genetic laboratories using standardized cfDNA sequencing methods. Pregnancy characteristics and outcomes were obtained from medical records and the national prenatal screening database. A true positive was defined as a high-risk NIPT result confirmed in the fetus or infant. The primary outcome was the diagnostic performance of NIPT for detecting trisomies 21, 18, and 13 and other chromosomal abnormalities. Among 981 vanishing-twin pregnancies, 655 met the inclusion criteria and underwent NIPT. Fifty-six pregnancies (8.5%) had abnormal results, including 29 major trisomies and 29 additional chromosomal findings. NIPT indicated high-risk for trisomy 21 in 17 cases, of which seven (41%) were confirmed in the surviving fetus. NIPT suggested high risk for trisomy 18 in 4 cases and trisomy 13 in 8 cases, but none were confirmed on follow-up testing. Additional chromosomal findings were reported in 29 pregnancies and were not confirmed in the surviving fetus. Discordant-positive results were more common when fetal demise occurred closer to the time of testing and decreased as the interval increased. In multiple pregnancies, NIPT also detected several cases of trisomy 21 in living twin and triplet gestations, most of which were confirmed with diagnostic testing. These findings suggest that NIPT can accurately detect trisomy 21 in multiple pregnancies and in the surviving fetus of vanishing-twin pregnancies. Abnormal NIPT results were more common in vanishing-twin pregnancies, likely reflecting cfDNA from the demised twin. Although NIPT indicated several cases of trisomy 18 and trisomy 13, none were confirmed in the surviving fetus. This likely reflects the lower viability of these aneuploidies and their higher association with confined placental mosaicism. Discordant-positive results became less likely as the interval between fetal demise and testing increased. Strengths include the large cohort and classification of vanishing-twin type. Limitations include the small number of trisomy 18 and 13 cases and the inability to evaluate sex chromosome abnormalities or triploidy. NIPT appears reliable for detecting trisomy 21 in vanishing-twin and multiple pregnancies, although evidence for other chromosomal abnormalities remains limited. (Summarized from van Eekhout JCA, Bax CJ, van Prooyen Schuurman L, et al. Performance of noninvasive prenatal testing in vanishing-twin and multiple pregnancies: Results of TRIDENT-2 study. Ultrasound Obstet Gynecol. 2025;66:738–746. doi: 10.1002/uog.70015)