Fetal intraabdominal umbilical vein varix (FIUV) is focal dilatation of the intrabdominalumbilical vein of thefetus. It appears as a round or fusiform cystic structure in thefetal abdomen, which shows continuity with the umbilical vein ongrayscale andcolor Dopplerimaging. The diagnostic criteria include the FIUV varix diameter at least 50% wider than the diameter of the intrahepatic umbilical veinand an intraabdominal umbilical vein diameter exceeding 9 mm orgreater than twostandard deviations above the mean for gestational age. We report three cases, two cases with isolated FIUV and favorable outcome and the third case with FIUV and atrioventricular septal defect, where trisomy 21 (Down syndrome) was diagnosed.