Cervical length refers to the length of the lower end of the uterus, which gradually shortens during pregnancy as the body prepares for labor. The length of the cervix during pregnancy is important because if it shortens too soon, it can increase the risk of preterm labor and premature birth. Preterm labor is defined as labor that begins between 20 weeks and 36 weeks and 6 days of pregnancy. A short cervix is one that is less than 25mm (2.5cm) long at around 20 weeks of pregnancy.

Doctors can measure cervical length using a transvaginal ultrasound, which is typically done between 18 and 20 weeks of pregnancy. If the ultrasound shows that the cervical length is less than 29 millimeters but greater than 25 millimeters, the healthcare provider might recommend more frequent ultrasounds to monitor the cervical length. If the cervical length is less than 25 millimeters, the healthcare provider might recommend interventions to reduce the risk of preterm labor, such as cervical cerclage, which involves placing a stitch in the cervix.

In summary, cervical length is the length of the lower end of the uterus, which gradually shortens during pregnancy. A short cervix, which is less than 25mm long at around 20 weeks of pregnancy, can increase the risk of preterm labor and premature birth. Doctors can measure cervical length using a transvaginal ultrasound and recommend interventions to reduce the risk of preterm labor if the cervical length is less than 25 millimeters.