Detection of fetal trisomy 9 mosaicism by noninvasive prenatal testing through maternal plasma DNA sequencing

Objective: Noninvasive prenatal testing (NIPT) is widely used as a powerful screening tool to detect common aneuploidies. However, its application for detection of rare chromosomal abnormalities remains inconclusive. Case report: A 38-year-old woman (gravida 2, para 0) requested NIPT as a primary screening test for fetal aneuploidies at 13 weeks and 1 day of gestation. An unexpected Trisomy 9 (T9) abnormality was highly suspected. Amniocentesis was arranged for further diagnosis at 18 weeks of gestation. Final karyotyping reported 47,XX,+9 [18]/46,XX [12], indicating 60% T9 mosaicism. Conclusion: This case shows strong evidence that NIPT can be a powerful screening tool to detect rare fetal trisomies at very early gestation. Keywords: Amniocentesis, Karyotyping, Maternal plasma DNA, Noninvasive prenatal testing, Trisomy 9 mosaicis