A case of mosaic trisomy 17 with inconsistent findings between noninvasive prenatal testing and genetic amniocentesis

Abstract

Objective: To report a case of mosaic trisomy 17 with inconsistent findings between noninvasive prenatal testing (NIPT) and genetic amniocentesis. Case report: A 34-year-old primigravid woman presented for antenatal care at 9 weeks of gestation. At 13 weeks, she opted for NIPT based on next-generation sequencing, which yielded a negative result. Five weeks later, fetal intracardiac calcification was observed, prompting genetic amniocentesis at 18 weeks. The initial amniocentesis revealed a karyotype of mos 47,XX,+17[5]/46,XX[25]inv(9) (p12q13) in 5 out of 30 colonies, suggesting possible pseudo-mosaicism. A repeat amniocentesis two weeks later confirmed mosaic trisomy 17 and inversion 9 of p12q13 in 10 out of 34 colonies from two cultures. Despite normal prenatal ultrasound findings, the patient chose to terminate the pregnancy due to the potential for severe clinical outcomes associated with mosaic trisomy 17. Postnatal work-up was declined. Conclusion: This case highlights the limitations of NIPT and the importance of confirmatory diagnostic testing. The findings underscore the need for meticulous genetic counseling and informed consent, particularly in cases with suspected chromosomal anomalies. © 2025