Cervical length refers to the measurement of the cervix, which is the lower part of the uterus connecting to the vagina. During pregnancy, the cervix plays a crucial role by remaining long and closed, effectively holding the developing fetus within the uterus. As pregnancy progresses, the cervix gradually softens and prepares for birth, but its stability is important throughout gestation. Measuring cervical length helps assess the cervix’s ability to maintain the pregnancy until term.
How and When it is Measured
Measuring cervical length is performed during pregnancy. Transvaginal ultrasound is the most accurate method, involving a small probe inserted into the vagina for a clear view and precise measurement of the closed cervical canal. While transabdominal ultrasound can visualize the cervix, transvaginal is preferred for its superior accuracy, as a full bladder can distort transabdominal scans. Measurements are commonly taken during the mid-trimester, typically between 18 and 24 weeks, often during the anatomy scan. Monitoring may begin around 16 weeks for higher-risk individuals.
Understanding Normal Measurements
A normal cervical length during pregnancy indicates the cervix is adequately supporting the developing pregnancy. In the mid-trimester, a cervical length of 2.5 centimeters (25 millimeters) or greater is considered normal. Typical lengths range from 3 to 5 centimeters. This measurement signifies the cervix is closed and stable, reducing concerns about early changes that could lead to preterm labor. A consistent normal length suggests the cervix is maintaining its structural integrity, necessary to keep the uterus sealed until term.
When Cervical Length is Short
A cervical length shorter than expected, generally less than 2.5 centimeters (25 millimeters) before 24 weeks, indicates a higher risk for complications during pregnancy. This is sometimes called cervical insufficiency, where tissues may be too weak to remain closed under increasing pregnancy pressure.
The main concern with a short cervical length is an increased risk of preterm birth, which is delivery before 37 weeks. This heightened risk occurs because a shorter cervix provides less structural support, making it more susceptible to early softening, shortening, and dilation. While many individuals with a short cervix still deliver at term, the risk of early delivery is significantly elevated. The earlier a short cervix is identified, and the shorter the measurement, the greater the potential risk of preterm birth.
Managing a Short Cervical Length
When a short cervical length is identified, medical interventions and close monitoring are often recommended to help prolong the pregnancy. Progesterone therapy, typically administered vaginally, is a common approach. This hormone helps relax uterine muscles and can reduce spontaneous preterm birth risk by preventing further cervical shortening. It is often prescribed daily until around 36 weeks for individuals with a short cervix and a singleton pregnancy.
A cervical cerclage is a surgical procedure involving a stitch around the cervix to reinforce and keep it closed. It is usually performed in the second trimester, often between 12 and 24 weeks, and removed closer to the due date. Cerclage is typically considered for individuals with a very short cervix or a history of preterm birth. Increased monitoring through more frequent transvaginal ultrasounds may also be recommended to track any changes. The choice of management strategy depends on individual factors, including cervical length, gestational age, and other risk factors for preterm birth.