The length of the cervical canal is greater than 25mm normal in late pregnancy and there is no specific requirement for the length of the cervical canal after 37 weeks. 1. Before 37 weeks: After entering the late stage of pregnancy, that is, after 28 weeks, and before 37 weeks of full-term pregnancy, the cervical canal should be greater than 25mm, otherwise it is called the cervical canal is too short. However, if the cervical canal is not less than 25mm, but there are symptoms of preterm labor, it is also necessary to seek medical treatment and hospitalization. 2. After 37 weeks: At this period, you are already in full-term labor, and there is no specific requirement for the length of the cervical canal. You need to count the fetal movements every day, have regular checkups, closely observe the changes in the course of labor, and wait for the delivery of the baby. Detecting the length of the cervix is a convenient way to prevent preterm labor caused by cervical insufficiency. If the cervix gradually shortens before 37 weeks of pregnancy and is accompanied by contractions, there is a risk of preterm labor, you need to consult the hospital in a timely manner, according to the situation of fetal preservation treatment, and need to stay in bed at the same time.