Velamentous cord insertion (VCI) is one type of cord insertion. The aberrant vessel of the VCI is very vulnerable, so VCI is known to bring a high risk of perinatal complications, such as low Apgar scores, stillbirth, preterm delivery, and small for gestational age (SGA). The incidence rate of VCI ranges from 0.5 to 2.4% in singleton pregnancies [
1]. Pregnancy followed by assisted reproductive technology was reported to significantly increase the incidence rate of VCI up to 12% [
2]. Early prenatal detection of VCI will make it easier to evaluate the several complications, such as SGA and perinatal death, and prevent bad perinatal outcomes [
3]. Prenatal diagnosis of VCI can usually be made if the site is seen to be away from the placenta, and the length of the aberrant vessel directly relates to the perinatal outcome [
4]. As such, it is very important to identify the insertion site to evaluate the risk. There is a report that when the insertion site is difficult to recognize, a sign of the branching vessels running through the fetal membranes will be an extra sign of VCI. This characteristic sign is referred to as the “mangrove sign” [
5]. …
