Ultrasound or cervical canal length measurement can be done, and the error of cervical canal measurement is smaller than ultrasound. When doing ultrasound to measure the length of the cervical canal, it is important to hold urine in moderation and not to overfill the bladder, which may compress the cervix and lead to large measurement errors. When doing ultrasound to measure the length of the cervical canal, be careful not to insert the probe into the vagina for too long because the cervical canal will not be displayed if it is inserted too long, and then the probe will easily squeeze the cervix, causing deformation of the cervix and inaccurate measurement. When doing ultrasound or cervical ultrasound, it is important to make sure that the inner and outer cervical canals are clearly displayed and that the measurement is done with the cervix in a natural stretching position. The length of the cervical canal in women of childbearing age is about 3 cm. When the cervical canal is too long, the uterine body should be carefully examined to exclude uterine dysplasia. When the cervical canal is too long, the opening of the uterus is slow to dilate during labor, which can easily lead to obstructed labor, and when the cervical canal is too short, it is less tolerable during pregnancy, which can easily lead to preterm labor.