The standard value of cervical canal length during pregnancy is between 25mm and 30mm. During pregnancy, as the fetus continues to grow and develop, the lower part of the uterus is elongated. The standard value of the length of the cervical canal during pregnancy is usually between 25mm and 30mm, which usually needs to be measured by transvaginal ultrasonography, and if there is an abnormal change in the length of the cervix, this is important for determining preterm labor. The risk of preterm labor is elevated when the cervical canal length is less than 25 mm in a 24-week pregnant woman and the endocervix forms a funnel; the risk of preterm labor is higher when the cervical canal length is less than 15 mm; and the risk of preterm labor is low when the cervical canal length of the pregnant woman is greater than 30 mm. Pregnant women with abnormal changes in cervical canal length should seek prompt medical attention to avoid delays that could lead to adverse pregnancy outcomes.