At 20 weeks the umbilical cord is wrapped around the neck and the placenta previa is in a transverse position with some risk. Umbilical cord bypass is a normal phenomenon, normally within two weeks there is no problem, more than three weeks will cause fetal hypoxia, asphyxia, there are some umbilical cord bypass will fall off by itself. You should go to the hospital for regular checkups and pay more attention to the fetal movement, which is normal and usually does not have any effect. Changes in the position of the placenta are related to factors such as damage to the uterine lining, damage to the placenta, and substandard quality of the fertilized egg. In case of transverse placenta previa, the fetus will be asphyxiated during delivery due to umbilical cord bypass, and it will also lead to hemorrhage, so it is important to do regular checkups during pregnancy to correct the fetal position. If the umbilical cord is wrapped around the neck and the transverse placenta previa continues to be unrelieved, it is necessary to consult a doctor in time to clarify the cause of the disease and carry out treatment under the guidance of the doctor.