Abstract
Karyotyping by invasive prenatal testing such as amniocentesis or chorionic villi sampling is the only definitive method of determining Down syndrome. However, both methods are associated with procedure-related risks. The combination of two noninvasive tools, the maternal serum triple screen and the ultrasound examination, provides a way of identifying fetuses at higher risk for Down syndrome. Ultrasound markers are sonographic findings that may exist as structural malformations or normal variants that are more prevalent in Down syndrome. Depending on the particular marker, either a single marker or a cluster may indicate an increased risk of an affected fetus. Sonographic markers include duodenal atresia, cardiac defects, brachycephaly, mild ventriculomegaly, flattened facial profile, thickened nuchal skin fold, fetal hydrops, hyperechoic bowel, choroid plexus cysts, pyelectasis, shortened extremities, echogenic intracardiac foci, greater iliac wing angle, and specific findings in the fetal hand and foot.