Cervical canal length during pregnancy is usually checked by ultrasound. A cervical length test during pregnancy is a test that is primarily used to prevent preterm labor. The cervical length of the cervix during pregnancy is usually measured by ultrasound imaging at around 23 weeks of pregnancy to determine the likelihood of preterm labor. A cervical length of more than 30 millimeters indicates a lower likelihood of preterm labor, while a cervical length of less than 25 millimeters indicates a higher likelihood of preterm labor. However, these are only approximate values, and there is no fixed clinical value for cervical canal length. Usually, the cervical canal length becomes shorter and shorter as the pregnancy progresses, and the cervical opening is gradually shortened and opened at the time of labor. To summarize, the examination of cervical canal length during pregnancy can only serve as a prognostic indicator, and patients are advised not to pay too much attention to it. However, if there are obvious discomfort symptoms, patients should go to the hospital in time for medical consultation.