In layman’s terms: the etiology of sail placenta is currently unknown and there are many hypotheses or theories. The placenta is a very sensitive organ to blood supply. When the blood flow to the placental attachment site decreases due to various factors (such as history of cesarean delivery or multiple miscarriages, causing endometrial damage, inflammation or atrophy), the placenta starts the process of slow migration to the fertile area of blood flow, thus leaving the umbilical cord alone, which is painfully separated but connected, and the silk is the fetal membrane, which is diffused within the fetal membrane. The umbilical cord blood vessels, lacking the protection of special structure (Huatong glue), are extremely fragile and weak, flattened when pressed and broken when pulled, resulting in very serious consequences, the most serious of which will lead to fetal death. Professionally, the etiology of sail-shaped placenta is unknown, but there are many unproven hypotheses or theories. Benirschke et al. suggest that the umbilical cord is normally attached to the basal meconium, which is rich in blood supply, in the early stage of embryonic development, but later, due to endometrial dysplasia or endometritis at the site of placental attachment, the lobulated chorionic membrane grows in the direction of rich blood supply, causing the originally normal cord to gradually change to a deviated position. At the same time, due to malnutrition of the placental cord attachment site, the chorionic villous membrane atrophies to smooth chorionic membrane, causing the cord to attach to the fetal membranes. The umbilical vessels adhering to the fetal membranes are fixed to the smooth chorionic membrane by the surrounding collagen and are prone to rupture due to the lack of protection of the surrounding warton glue. Current research suggests that multiple pregnancies are a high risk factor for sailiform placenta, which occurs in 0.24% to 1.80% of singleton pregnancies, up to 9% of twin pregnancies, and mostly sailiform attachment in three or more pregnancies. Placental abnormalities such as placenta praevia, bilobed or multilobed placenta, and parietal placenta are also risk factors for the occurrence of sailiform placenta.