The cervix is the thick, muscular lower segment of the uterus that remains long, firm, and closed throughout pregnancy to protect the developing fetus. When the cervix is unable to sustain this barrier function, it can prematurely shorten, thin, and open under the weight of the growing pregnancy. This condition is medically termed cervical insufficiency, sometimes referred to as a “weak cervix,” and represents a structural or functional defect that prevents it from retaining the fetus.
Defining Cervical Insufficiency and Symptoms
Cervical insufficiency is defined by the painless dilation and effacement of the cervix, typically occurring in the second trimester without uterine contractions. This premature opening can lead to mid-trimester pregnancy loss or spontaneous preterm birth before 37 weeks gestation. Because there are no painful contractions, the condition is often difficult to detect until it has progressed significantly.
While some individuals are asymptomatic, others might experience subtle warning signs days or weeks before dilation occurs. These symptoms can include a feeling of pressure or heaviness in the pelvis, a dull ache in the lower back, or mild abdominal cramping. A noticeable change in vaginal discharge, such as an increase in thin, watery, or pink-tinged fluid, may also be reported.
Underlying Causes and Risk Factors
The underlying cause of cervical insufficiency is often a structural weakness in the cervical tissue that compromises its tensile strength. This weakness can be acquired due to previous damage or be a condition present from birth.
Trauma resulting from prior gynecological procedures is a frequent acquired cause. These procedures include a loop electrosurgical excision procedure (LEEP) or a cone biopsy, which remove abnormal cervical cells. Procedures like dilation and curettage (D&C), which involve mechanical widening of the cervix, can also contribute to weakness.
Previous obstetric events are another risk factor, particularly a history of spontaneous preterm birth or second-trimester pregnancy loss. Cervical lacerations that occurred during a difficult delivery, even if repaired, can compromise tissue integrity. Less common causes include congenital factors, such as structural abnormalities of the uterus and cervix known as Müllerian duct defects. Rare genetic conditions that affect collagen, the fibrous protein that provides much of the cervix’s strength, like Ehlers-Danlos syndrome, can also predispose an individual to insufficiency.
Procedures Used for Diagnosis
Cervical insufficiency is typically diagnosed during pregnancy using medical history and physical assessment. The primary diagnostic tool is a transvaginal ultrasound (TVUS), which uses a thin, wand-like device placed in the vagina to accurately measure cervical length. This non-invasive measurement allows clinicians to monitor for premature shortening or funneling, which is the ballooning of the fetal membranes into the cervical canal.
A cervical length of less than 25 millimeters before 24 weeks is considered abnormally short and indicates a risk for preterm birth. For those at high risk, such as those with a prior preterm birth, serial TVUS measurements may be performed every one to two weeks between 16 and 24 weeks. A physical examination can also reveal advanced effacement or dilation, or show the amniotic sac bulging through the cervical opening.
Treatment Options
Management of cervical insufficiency centers on mechanical reinforcement and pharmacological support to extend the pregnancy. The primary mechanical intervention is a cervical cerclage, a minor surgical procedure where a strong, non-absorbable suture is placed around the cervix to keep it closed. This stitch is typically placed high on the cervix near the internal opening, acting like a purse-string to reinforce the structure.
Cerclage procedures are categorized by indication:
- History-indicated cerclage is placed electively before 14 weeks due to a history of multiple losses.
- Ultrasound-indicated cerclage is placed when monitoring reveals a short cervix (less than 25 millimeters) before 24 weeks.
- Rescue or emergency cerclage may be performed later in the second trimester when the cervix has already begun to dilate and the fetal membranes are bulging.
The sutures are removed around 36 to 37 weeks, allowing for labor and delivery.
Progesterone therapy is a pharmacological approach often used alongside or instead of cerclage, depending on the patient’s history and cervical length. The hormone is usually administered vaginally as a gel or suppository daily. This is thought to help maintain uterine quiescence by suppressing contractions and reducing inflammation. This therapy is beneficial for individuals with a short cervix who do not have a prior history of spontaneous preterm delivery.
For those with a history of preterm birth, progesterone supplementation may begin between 16 and 24 weeks and continue until 36 weeks. Other non-surgical management includes close monitoring with ultrasound and sometimes a pelvic rest recommendation. Strict bed rest is often controversial and not universally recommended. In cases where a cerclage is not possible or has failed, a pessary—a device that fits inside the vagina to lessen pressure on the cervix—may be used, though more research is needed on its effectiveness.