2025 Volume 61 Issue 2 Pages 335-339
Noninvasive prenatal genetic testing（NIPT）is a nonconfirmatory test. We report a case of a false-positive NIPT result due to a supernumerary marker chromosome derived from chromosome 18.
Case: A 44-year-old G4P3 woman. She requested prenatal diagnosis and was referred to our hospital at 10 weeks and 5 days’ gestation. After genetic counseling, NIPT was performed. The result was positive for trisomy 18. Amniocentesis was performed. The chromosome analysis revealed a 47,XX,＋mar.ish der（18）（D18Z1＋）dn karyotype. The chromosome karyotypes of both parents were normal, and the marker chromosome was found to be de novo. The marker chromosome was derived from the centromere region of chromosome 18, and as it is extremely small, it was thought that the risks of clinically significant symptoms were fewer than the general risks. At 38 weeks and 3 days’ gestation, a cesarean section was performed to prevent the rupture of a maternal aneurysm. The baby was a 2,568-g girl. She had a normal phenotype at birth, and no developmental disorder was observed at the age of 3 years.
