Prenatal diagnosis of trisomy 9

Fetal trisomy 9, especially its nonmosaic form, is a rare chromosomal abnormality and there are only 8 cases reported to have been sonographically detected in the prenatal period. We report a case of nonmosaic fetal trisomy 9, mimicking trisomy 13 on sonographic findings at 32 weeks' gestation. Although the incidence of trisomy 9 is rare, diagnosing trisomy 9 is important because the sonographic features are similar to those of trisomies 13 and 18, and cannot to be identified by routine fluorescencein situ hybridization. Because nonmosaic trisomy 9 is universally lethal, correct diagnosis and appropriate counseling is essential in patient care and clinical management.