The length of the cervical canal of the uterus is normally >35 mm and changes accordingly when pregnancy occurs. In case of cervical insufficiency, there is a significant shortening of the cervical canal. If the length of the cervical canal is measured to be <25 mm, and in conjunction with the different weeks of gestation, it is determined whether there is a significant change in the function of the cervical canal. It is also important to determine whether the cervical canal is curved or conical in shape, and if it is conical, to determine the height and width of the cone to further determine whether cervical insufficiency exists. If the possibility of cervical insufficiency is considered, cervical cerclage should be performed at the appropriate gestational age to allow the pregnancy to proceed more smoothly backwards.