Abstract:Objective: To evaluate the value of ultrasonography in diagnosis of the fetus with trisomy 18 in the second trimester. Methods: Reviewing the data of the prenatal ultrasonography of 57 fetuses with trisomy 18 syndrome, which were finally diagnosed by karyotype analysis at our hospital in the past thirteen years, exploring the sonographic indicators which were helpful for the diagnosis of this disease. Results: Abnormal ultrasonographic findings included ventricular septal defect, choroid plexus cyst, intrauterine growth retardation, overlapping fingers, strawberry-shaped head, single umbilical artery, abnormal foot, polyhydramnios, cerebellar hypoplasia, low-set ears, nose abnormality, the rate of which is 46%, 44%, 42%, 40%, 33%, 33%, 26%, 23%, 21%, 16%, 12% and 11% respectively. About 89% of fetuses have abnormal ultrasonographic findings, 82% of fetuses showed two or more anomalies. Conclusions: Ultrasonography is effective at detection of fetuses with trisomy 18 syndrome in the second trimester, which can improve the prenatal diagnosis of fetus with trisomy 18 syndrome and decrease the birth rate of fetus with trisomy 18 syndrome in combination with karyotype analysis.