During pregnancy, it is normal for the length of the cervix to be between 25-30mm, which does not change much during normal times and during pregnancy. It is best if the length of the cervix is greater than 30mm. If the length is too short, shorter than 25mm it can easily lead to cervical insufficiency, preterm miscarriage or premature birth, or even repeated spontaneous abortion. If the cervical canal is detected to be too short during pregnancy, it is treated with cervical ring sutures and birth control medication in the middle of pregnancy, and the sutures are removed at 37 weeks of pregnancy to improve the survival rate of the fetus during pregnancy. Normally, the cervical canal is within the normal length of a woman’s cervix, and during labor, due to uterine contractions, the cervical canal is gradually reduced, shortened and opened up by the pressure of the fetus and amniotic fluid, so that the fetus can pass through the cervix and deliver vaginally.