Sonographic detection of fetuses with trisomies 13 and 18: accuracy and limitations.

Nine fetuses having trisomy 13 and 15 fetuses with trisomy 18 were diagnosed by cytogenetic studies and also underwent a sonogram between 15 and 40 weeks. All nine fetuses with trisomy 13 had been prospectively identified as having sonographic findings suggestive of trisomy 13. Twelve of the 15 fetuses with trisomy 18 had sonographic abnormalities compatible with trisomy 18. Findings included abnormalities of the face and head, extremities, and diaphragmatic hernia. This report examines criteria for the ultrasound diagnosis of trisomies 13 and 18 and describes the accuracy of prenatal sonography for these diagnoses.