Residency · Residency · Obstetrics Gynecology

Cervical Insufficiency and Cerclage

Definition and Pathophysiology

Cervical insufficiency is the inability of the cervix to retain a pregnancy in the second trimester in the absence of uterine contractions or labor. The older term "incompetent cervix" has largely been replaced. The condition results from structural weakness of the cervical stroma, specifically its collagen and smooth muscle components. The classic presentation is painless cervical dilation with prolapse of the amniotic membranes in the mid-trimester, often leading to previable delivery.

Etiology

The causes of cervical insufficiency may be acquired, congenital, or inflammatory. Acquired causes include prior cervical surgery (LEEP, cold knife cone biopsy, or aggressive mechanical dilation during D&C) and cervical lacerations sustained during a prior delivery. Congenital causes include in utero DES exposure, Mullerian anomalies, and connective tissue disorders such as Ehlers-Danlos syndrome. Ascending infection and inflammation may also weaken the cervical barrier. Many cases remain idiopathic.

Diagnosis

Clinical Diagnosis

There is no single definitive diagnostic test for cervical insufficiency. The diagnosis is primarily historical, based on a classic obstetric history of one or more prior second-trimester pregnancy losses characterized by painless cervical dilation. Other causes of second-trimester loss -- including infection, abruption, and preterm labor with contractions -- must be excluded.

Ultrasound Surveillance

Transvaginal cervical length (TVCL) measurement is the primary surveillance tool. Normal cervical length at 16 to 24 weeks is 35 to 40 mm. A short cervix is defined as less than 25 mm, which is the threshold used in most intervention studies. Funneling refers to dilation of the internal os while the external os remains closed, producing a V-shaped or U-shaped configuration. Dynamic cervical shortening can sometimes be demonstrated with fundal pressure or the Valsalva maneuver.

<image>Transvaginal ultrasound images showing progressive cervical shortening and funneling: normal cervix (40mm, closed internal os), early funneling (Y-shaped, 28mm functional length), and advanced funneling (U-shaped, 15mm functional length) with prolapsing membranes</image>

Management Options

History-Indicated (Prophylactic) Cerclage

A history-indicated cerclage is placed prophylactically in women with a history of one or more prior second-trimester pregnancy losses consistent with cervical insufficiency or a prior cerclage placed for cervical insufficiency. It is performed at 12 to 14 weeks' gestation after first-trimester viability has been confirmed. The McDonald technique uses a purse-string suture of nonabsorbable material (Mersilene tape or Prolene) placed at the cervicovaginal junction. The Shirodkar technique involves submucosal dissection with suture placement at or near the internal os, achieving a theoretically higher placement but at the cost of greater technical complexity. The cerclage is removed at 36 to 37 weeks, or earlier if labor develops, PPROM occurs, or infection is identified.

Ultrasound-Indicated (Rescue of Short Cervix) Cerclage

An ultrasound-indicated cerclage is placed when a short cervical length (below 25 mm) is detected on TVCL at 16 to 23 weeks 6 days in a patient with a history of prior spontaneous preterm birth. The McDonald technique is most commonly used. Evidence from multiple trials and meta-analyses supports the benefit of cerclage in this specific population -- singleton gestation with both a prior preterm birth and a short cervix. Critically, cerclage has no proven benefit for patients with a short cervix but no prior preterm birth history. In that scenario, vaginal progesterone is the preferred intervention.

Physical Exam-Indicated (Rescue/Emergency) Cerclage

A rescue cerclage is considered when cervical dilation (typically 1 to 4 cm) with visible or prolapsing membranes is discovered on physical examination in the mid-trimester, without evidence of active labor or infection. This is a higher-risk procedure with lower success rates than elective cerclage, but it can significantly prolong the pregnancy. The technique involves gentle reduction of the membranes (using Foley catheter inflation, Trendelenburg positioning, or amniocentesis to reduce pressure) followed by cerclage placement. Chorioamnionitis must be excluded before proceeding, typically through amniocentesis for cell count, glucose, Gram stain, and culture. Perioperative antibiotics are commonly administered, and tocolysis with indomethacin is often used.

Transabdominal Cerclage

A transabdominal cerclage is indicated when transvaginal cerclage has failed, when the cervix is very short or absent (as after trachelectomy or extensive conization), or when cervical anatomic abnormalities prevent adequate transvaginal suture placement. It is placed via laparotomy or laparoscopically, ideally before conception or in early pregnancy (8 to 12 weeks). The suture is positioned at the level of the internal os at the cervicoisthmic junction. Because the suture cannot be removed vaginally, cesarean delivery is required. The suture may be left in situ for future pregnancies or removed at the time of cesarean.

Cerclage Technique: McDonald Procedure

Steps

The procedure is performed in the lithotomy position under spinal or general anesthesia. The cervix is exposed with retractors and grasped with ring forceps on the anterior and posterior lips. A purse-string suture (typically 5 mm Mersilene tape) is placed as high on the cervix as possible, close to the internal os. Four to five bites are taken through the cervical stroma, carefully avoiding the cervical canal and the cervical branch vessels. The knot is tied anteriorly for accessibility at the time of removal, and long suture tails are left for later identification.

Perioperative Considerations

Preoperative cervical cultures should be obtained and any infection treated. Perioperative indomethacin for 24 to 48 hours is commonly used to reduce prostaglandin-mediated contractions, though this practice is somewhat controversial. After placement, pelvic rest is maintained (no intercourse, no heavy lifting). Serial TVCL monitoring follows the cerclage, typically every 2 weeks initially and then monthly.

<image>Surgical illustration of the McDonald cerclage technique showing the purse-string suture placement around the cervix near the internal os, with labeled anatomical landmarks including the external os, cervical stroma, and suture knot tied anteriorly</image>

Vaginal Progesterone vs. Cerclage

Short Cervix Without Prior Preterm Birth

For singleton gestations with a short cervix but no history of prior preterm birth, vaginal progesterone (200 mg suppository or 90 mg gel nightly) is the first-line intervention. It reduces preterm birth by approximately 40% in this population. There is no role for cerclage in these patients.

Short Cervix WITH Prior Preterm Birth

When a short cervix is identified in a patient with a history of prior spontaneous preterm birth, cerclage is the primary intervention. Vaginal progesterone may be added as an adjunct. No head-to-head trial has definitively demonstrated the superiority of one approach over the other in this specific population.

Cervical Pessary

The Arabin pessary is a silicone device placed around the cervix. Some randomized controlled trials have shown benefit, while others have not, and the data remain conflicting overall. It is not currently recommended as standard practice by ACOG but may be considered in research settings or when cerclage is contraindicated.

Twin Gestations

Short cervix in twin gestations carries increased preterm birth risk, but the management approach differs fundamentally from singletons. Cerclage is not recommended for twin gestations with a short cervix, as available evidence suggests it may worsen outcomes. Vaginal progesterone for twins with a short cervix has some support from meta-analyses suggesting modest reductions in neonatal morbidity, but the data are mixed. Cervical pessary in twins has also produced conflicting results across trials.

Complications of Cerclage

The most common serious complication of cerclage is premature rupture of membranes, occurring in approximately 5 to 10% of cases. Other complications include chorioamnionitis (with higher risk in rescue cerclage), cervical laceration or stenosis, suture displacement or erosion, preterm labor, and rarely bladder injury (more common with the Shirodkar technique).

Cerclage Removal

Elective removal is performed at 36 to 37 weeks. Emergent removal is indicated for PPROM, active preterm labor unresponsive to tocolysis, chorioamnionitis, or significant vaginal bleeding. Labor often follows cerclage removal within 24 to 48 hours, though this is not universal. If a cerclage is retained during active labor, there is a risk of cervical laceration and uterine rupture.

Clinical Pearls

Cervical insufficiency is a clinical diagnosis based on obstetric history. There is no definitive diagnostic test, and the diagnosis should be supported by a classic pattern of painless second-trimester pregnancy loss.

The key clinical distinction for cerclage decision-making is that ultrasound-indicated cerclage requires both a short cervix and a history of prior spontaneous preterm birth. Neither finding alone is sufficient.

A short cervix in a patient with no prior preterm birth history is managed with vaginal progesterone, not cerclage.

Cerclage is contraindicated in twin gestations with a short cervix.

Chorioamnionitis must always be ruled out before placing a rescue cerclage. Amniocentesis for cell count, glucose, Gram stain, and culture is the recommended evaluation.

Transabdominal cerclage mandates cesarean delivery because the suture cannot be removed transvaginally.

With the FDA withdrawal of 17-OHPC in 2023, cerclage and vaginal progesterone remain the primary tools for preterm birth prevention in at-risk patients.

References

• ACOG Practice Bulletin No. 234: Prediction and Prevention of Spontaneous Preterm Birth (2021)
• ACOG Practice Bulletin No. 142: Cerclage for the Management of Cervical Insufficiency (2014, reaffirmed 2021)
• Berghella V et al. Cerclage for short cervix on ultrasonography: meta-analysis. Obstet Gynecol. 2011;117:663-671
• Romero R et al. Vaginal progesterone for preventing preterm birth and adverse perinatal outcomes in singleton gestations with a short cervix: a meta-analysis. Am J Obstet Gynecol. 2018;218:161-180
• Saccone G et al. Cerclage for short cervix in twin pregnancies: systematic review and meta-analysis. Obstet Gynecol. 2015;126:1162-1168

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