A cervical length of less than 1 cm usually indicates that labor is imminent. Normally, it is normal for a woman to have a cervical length of 2.5-3 cm after pregnancy. In late pregnancy, after labor or in case of preterm labor, the cervical canal will gradually shorten due to the squeezing of the fetal head down and the rhythmic contraction of the uterus, until the cervical canal flattens and the opening of the uterus begins to expand. In women with cervical insufficiency, if the length of the cervical canal is shorter than 1.5 cm, spontaneous abortion can easily occur in the middle of pregnancy, and the cervical cerclage should be performed during the 14-16 weeks of pregnancy, and then removed in the late pregnancy to await natural delivery.