A short cervix during pregnancy represents a significant risk requiring careful management to prolong gestation and improve outcomes for the baby. The cervix, the lower part of the uterus, normally remains long, firm, and closed, acting as a structural barrier. Premature shortening, often defined as less than a specific measurement threshold, is a major marker for cervical insufficiency and an increased risk of preterm birth (before 37 weeks). The goal of medical management is not to physically “increase” the length, but to stabilize and maintain the current length to prevent further shortening and premature dilation.
Diagnosis and Measurement of Cervical Length
The most accurate method for assessing and monitoring cervical length is the transvaginal ultrasound (TVUS) examination. This procedure uses a specialized probe placed gently into the vagina to obtain clear, precise images of the cervix, avoiding distortion from a full bladder common in abdominal scans. Length is measured as the distance between the internal opening (closest to the uterus) and the external opening (closest to the vagina).
Screening for a short cervix is most commonly performed during the mid-trimester, typically between 16 and 24 weeks of gestation. This timing is optimal because it allows for early detection and intervention before the cervix begins to open. A measurement of less than 25 millimeters (2.5 centimeters) is considered a short cervix and raises concern for an elevated risk of spontaneous preterm birth.
The ultrasound technique requires precision, including ensuring the bladder is empty and avoiding excessive pressure with the probe, which could falsely lengthen the measurement. Sonographers take a minimum of three measurements and report the shortest, most stable length observed. The presence of “funneling,” where the internal opening widens into a V or U shape, is also noted, as this indicates a loss of structural integrity and contributes to the risk assessment.
Primary Medical Interventions to Maintain Length
Once a short cervix is identified, medical professionals use several proven strategies to maintain the cervical barrier and prolong the pregnancy. These interventions are designed to reduce the risk of spontaneous preterm delivery and are chosen based on the woman’s history and the degree of cervical shortening.
Progesterone Therapy
Progesterone is often the first-line treatment recommended for women with a short cervix, especially those carrying a single baby. This hormone helps maintain uterine quiescence by calming the uterus and reducing contractions, which stabilizes the cervix. The medication is typically administered daily as a vaginal suppository or gel, delivering the progesterone directly to the local tissues.
Treatment with vaginal progesterone usually begins upon diagnosis in the mid-trimester and continues until around 36 weeks of gestation. Clinical trials have demonstrated that this therapy significantly reduces the rate of preterm birth before 33 weeks in women with a short cervix. For women with a cervical length of 20 millimeters or less, vaginal progesterone is a recommended option to improve neonatal outcomes.
Cervical Cerclage
Cervical cerclage is a surgical procedure involving placing a strong stitch around the cervix to reinforce its structure and mechanically keep it closed. This option is generally reserved for women with a history of prior spontaneous preterm birth, second-trimester loss, or an extremely short cervix (often less than 10 millimeters). The stitch acts as a supportive purse-string, physically preventing the cervix from opening under the pressure of the growing pregnancy.
The procedure is typically performed between 12 and 24 weeks of gestation, with timing depending on the indication. A history-indicated cerclage is placed early, while an ultrasound-indicated cerclage is placed after a short cervix is confirmed by a scan. The cerclage is removed electively around 36 to 37 weeks, allowing for a vaginal delivery, or earlier if labor begins spontaneously.
Cervical Pessary
A cervical pessary is a non-surgical option involving placing a small, flexible silicone device into the vagina to encircle the cervix. The device is hypothesized to work by physically supporting the cervix and changing the angle of the cervical canal. This redirects the weight of the pregnancy off the internal opening, which may help reduce pressure and prevent premature effacement.
The use of the pessary is less standardized than progesterone or cerclage, but it may be considered in cases where women prefer to avoid surgery. The device is typically inserted in the mid-trimester and remains in place until closer to term, similar to the duration of progesterone therapy. Research on its effectiveness has produced mixed results, so it is often discussed as an alternative or supplementary measure.
Ongoing Management and Follow-Up Care
After a short cervix is diagnosed and intervention is initiated, close follow-up care is necessary to monitor the pregnancy. Women with a history of preterm birth or those starting treatment often have serial transvaginal ultrasounds, typically every one to two weeks, to track cervical length until about 24 weeks gestation. Monitoring after this point is generally not recommended, as interventions are less effective later in pregnancy.
Activity modification is a common recommendation, which may include avoiding activities that place strain on the cervix, such as heavy lifting and strenuous exercise. Pelvic rest, meaning abstaining from sexual intercourse and inserting anything into the vagina, is also often advised to reduce local irritation and the risk of infection. Strict bed rest has not been shown to improve outcomes and is generally discouraged due to potential risks like blood clots.
Patient education is an important part of the management plan, focusing on recognizing the early signs of preterm labor. Women are taught to watch for symptoms such as persistent menstrual-like cramping, pelvic pressure, unusual vaginal discharge, or a sudden onset of backache. Recognizing these symptoms allows for immediate medical attention, which can lead to further interventions, such as medications to temporarily stop contractions or steroids for the baby’s lung development.