A short cervix is a medical finding during pregnancy concerning the length of the muscular canal connecting the uterus to the vagina. This structure normally remains long and firm throughout gestation to keep the pregnancy contained until term. A cervix is considered short when its length measures 25 millimeters (mm) or less, particularly when measured before 24 weeks of pregnancy. This measurement is the threshold indicating an increased risk of complications. The primary concern associated with a short cervix is a heightened chance of spontaneous preterm birth, defined as delivery occurring before 37 weeks of gestation.
Physical Signs That May Indicate Concern
Many individuals with a short cervix experience no noticeable symptoms, meaning the condition is often discovered incidentally during routine medical checks. However, certain physical changes warrant discussion with a healthcare provider. A subtle sign can be a feeling of unusual pressure or heaviness deep within the pelvis, sometimes described as general discomfort. This sensation may be accompanied by a persistent, dull ache in the lower back that is new or different from typical pregnancy aches.
Changes in vaginal discharge, such as an increase in volume or an alteration in consistency, are also commonly reported. Additionally, light spotting or minimal vaginal bleeding during the second trimester may prompt medical evaluation. These symptoms are common during pregnancy and are not diagnostic alone, but they should prompt a conversation about cervical length assessment.
Medical Screening and Measurement
Determining the precise length of the cervix requires an objective medical procedure. The gold standard for this measurement is the transvaginal ultrasound (TVUS). This technique involves inserting a slender ultrasound probe into the vagina, providing a clear, close-up image of the cervix without interference from the abdominal wall. The TVUS measures the length from the internal opening (os) to the external opening of the cervix, offering the most accurate result.
Screening for a short cervix is typically performed in the mid-trimester, often between 18 and 24 weeks of pregnancy, either during a routine anatomy scan or for high-risk patients. A measurement of 25 mm or less indicates a significantly elevated risk of preterm birth. If the cervix measures between 20 and 25 mm, it is considered short, and a measurement below 20 mm is associated with a substantially higher probability of early delivery.
While an abdominal ultrasound can sometimes visualize the cervix, this method is less reliable for accurate length determination. The abdominal approach frequently overestimates the cervical length, especially when the cervix is truly short, potentially leading to a missed diagnosis. If a screening abdominal ultrasound suggests a short cervix or the provider cannot get a clear view, a transvaginal ultrasound is recommended to obtain a definitive measurement.
Factors That Increase the Likelihood
Several historical and anatomical factors can predispose a person to developing a short cervix or experiencing an early delivery. The most significant predictor is a history of a previous spontaneous preterm birth, which substantially increases the chance of recurrence. Other factors that impact cervical integrity include:
- Past second-trimester pregnancy loss.
- Procedures involving the cervix, such as a Loop Electrosurgical Excision Procedure (LEEP) or a cone biopsy, used to remove abnormal tissue.
- Damage to the cervix during a difficult previous delivery.
- Congenital malformations of the uterus, such as a bicornuate or septate uterus.
- Multiple gestation pregnancy, which places greater strain on the cervix.
Management Strategies Following Diagnosis
Once a short cervix is confirmed, healthcare providers initiate specific management strategies aimed at prolonging the pregnancy. The most common intervention is progesterone supplementation, typically administered as a vaginal gel or suppository. This hormone therapy is usually started shortly after diagnosis and continued daily until around 36 weeks of gestation to maintain uterine quiescence.
For individuals with a particularly short cervix or a history of prior preterm birth, a cervical cerclage may be recommended. This surgical intervention involves placing a strong stitch around the cervix to physically reinforce and keep it closed. The cerclage is typically performed before 24 weeks and is removed near the end of the pregnancy.
Providers may also suggest increased monitoring through serial transvaginal ultrasounds to track further changes. While strict bed rest is not supported by evidence, modifications to physical activity may be advised. Another option is the use of a cervical pessary, a silicone device inserted into the vagina for external support.