A small cervix, sometimes called a "short" cervix, refers to a cervix that is less than three centimeters long during pregnancy. According to BabyZone, the length of the cervix during pregnancy should be greater than or equal to three centimeters.
According to The Bump, the cervix is the neck of the uterus and remains tightly closed while pregnancy lasts. However, during labor, it thins out and dilates to about 10 centimeters so that the baby can easily make its way into the world. The Mayo Clinic notes that a short cervix often indicates that that a woman has an increased risk of preterm labor and premature delivery.