What is the purpose and procedure of a cerclage in pregnancy?

Cervical Cerclage: Purpose and Procedure in Pregnancy

Cervical cerclage is a surgical procedure that involves placing a stitch around the cervix to provide mechanical support and prevent preterm birth in women with cervical insufficiency. 1 This intervention is one of the few effective measures available for preventing preterm delivery caused by cervical insufficiency, thereby reducing neonatal morbidity and mortality rates.

Indications for Cerclage

The main indications for cervical cerclage include:

1. History-indicated cerclage:

   • Women with 3 or more previous preterm deliveries and/or second-trimester pregnancy losses 2
   • Singleton pregnancies with prior spontaneous preterm birth and cervical length ≤25 mm before 24 weeks gestation 1

2. Ultrasound-indicated cerclage:

   • Short cervical length (<25 mm) detected on ultrasound before 24 weeks in women with history of prior spontaneous preterm birth or mid-trimester miscarriage 1
   • Women with extremely short cervix (<10 mm) may benefit significantly, with decreased preterm birth rates at <35 weeks compared to no cerclage (39.5% vs 58.0%) 1

3. Physical exam-indicated (rescue) cerclage:

   • For women who present with exposed membranes prolapsing through the cervical os 2
   • This type carries higher risk of infectious morbidity and should be considered on an individual case basis

Procedure Types

There are two main types of cervical cerclage procedures:

1. Transvaginal cerclage:

   • McDonald technique: Involves placing a purse-string suture around the cervix at the level of the internal os
   • Shirodkar technique: Involves placing the suture higher, closer to the internal os, with dissection of the bladder and burial of the knot

2. Transabdominal cerclage:

   • Performed when transvaginal cerclage has failed (delivery before 28 weeks after a history or ultrasound-indicated cerclage) 2
   • Can be performed before pregnancy or in the first trimester with similar outcomes
   • Can be considered up to 22 weeks gestation 1

Effectiveness and Outcomes

Cervical cerclage has been shown to:

• Reduce preterm birth rates at multiple gestational age thresholds, including births before 37,34,28, and 24 weeks 1
• Decrease preterm birth by approximately 30% before 35 weeks 1
• Probably reduce the risk of perinatal death compared with no cerclage 3
• Reduce neonatal morbidity and mortality in women with a history of cervical insufficiency or prior preterm birth 1

Post-Cerclage Management

After cerclage placement:

• Serial sonographic measurement of the cervical length is not routinely recommended 4
• Bed rest is discouraged 4
• Routine use of antibiotics, tocolysis, and progesterone is not recommended 4
• If preterm labor becomes established, the cerclage should be removed 4
• In normal pregnancies without complications, cerclage removal is typically considered at 36-37 weeks in women anticipating a vaginal delivery 2

Special Considerations

• In women with preterm prelabor rupture of membranes (PPROM), cerclage management is controversial. A single randomized trial showed no evidence of pregnancy prolongation with cerclage retention compared to removal, and there may be an associated risk of infectious morbidity with retention 5
• For women with PPROM, it is reasonable to either remove the cerclage or leave it in situ after discussing the risks and benefits with the patient 5
• In subsequent pregnancies after a history of previable PPROM, history-indicated cerclage should be reserved for individuals with classic historical features of cervical insufficiency or an unexplained second-trimester loss in the absence of placental abruption 5

Cervical cerclage remains an important intervention for preventing preterm birth in selected high-risk women, though its application continues to evolve as our understanding of the preterm birth syndrome develops.