Fetal single umbilical artery means that the fetus has only 1 umbilical artery. It may be caused by fetal chromosomal abnormality, poor development of the umbilical artery during embryonic period, and thrombosis. 1. Chromosomal abnormality: Various endogenous or exogenous factors can cause chromosomal abnormality, which can lead to atresia of one umbilical artery and the appearance of fetal single umbilical artery. 2. Embryonic dysplasia of the umbilical artery: dysplasia and atrophy of one umbilical artery in the early stage of embryonic development or temporary appearance of a single umbilical artery in the early stage of embryonic development may lead to single umbilical artery in the later stage of the fetus. 3. Thrombus: If a thrombus blocks one umbilical artery, it may cause it to atrophy, which may lead to single umbilical artery in the fetus. If the ultrasound examination reveals only this factor of single umbilical artery without other structural abnormalities, the prognosis of the newborn is good. If there are other ultrasound structural abnormalities at the same time, there is an increased risk of chromosomal aneuploidy as well as other malformations, such as renal hypoplasia, absence of anus, and vertebral defects. A decision on the need to terminate the pregnancy needs to be made under medical supervision.