Importance Fetal umbilical vein aneurysm is an uncommon anomaly that accounts for approximately 4% of umbilical cord abnormalities. The rate of intrauterine fetal death is reported to be approximately 4% to 5%, higher than the background rate of 0.7% that is generally reported during pregnancy. Objective The aim of this study was to review the pathophysiology, diagnosis, and clinical management of fetal umbilical vein aneurysm. Evidence Acquisition Advances in high-resolution ultrasound combined with color Doppler and 3-dimensional rendering have contributed to an increased understanding of the fetal venous circulation in recent years. Results When the diagnosis of umbilical vein aneurysm is made, the patient should undergo a detailed ultrasound evaluation of the fetal anatomy, including fetal echocardiography, to exclude associated anomalies. Amniocentesis should be offered when other anomalies are found. Patients should be informed about the potential for an unfavorable outcome of pregnancy and should undergo close ultrasound surveillance to assess the size of the aneurysm, as well as any evidence of thrombosis or signs of hydrops. Conclusions The main prognostic feature associated with a poor outcome of umbilical vein aneurysm seems to be the presence of other anomalies. Early diagnosis is associated with a somewhat worse prognosis, and most fetal deaths have been observed between 27 and 30 weeks of gestation. In the third trimester, it is reasonable to perform serial ultrasound examinations to assess fetal growth, the size of the aneurysm, and the blood flow pattern within the aneurysm.