Merck Manual

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Cervical Insufficiency


Antonette T. Dulay

, MD, Main Line Health System

Last full review/revision Jun 2019| Content last modified Jun 2019
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Cervical insufficiency (formerly called cervical incompetence) is painless cervical dilation resulting in delivery of a live fetus during the 2nd trimester. Transvaginal cervical ultrasonography during the 2nd trimester may help assess risk. Treatment is reinforcement of the cervical ring with suture material (cerclage).

Cervical insufficiency refers to presumed weakness of cervical tissue that contributes to or causes premature delivery not explained by another abnormality. Estimated incidence varies greatly (1/100 to 1/2000).


The cause of cervical insufficiency is not well-understood but seems to involve some combination of structural abnormalities and biochemical factors (eg, inflammation, infection); these factors may be acquired or genetic.

Risk factors

Most women with cervical insufficiency do not have risk factors; however, the following risk factors have been identified:

  • Congenital disorders of collagen synthesis (eg, Ehlers-Danlos syndrome)

  • Prior cone biopsies (particularly when 1.7 to 2.0 cm of the cervix was removed)

  • Prior deep cervical lacerations (usually secondary to vaginal or cesarean delivery)

  • Prior excessive or rapid dilation with instruments (now uncommon)

  • Müllerian duct defects (eg, bicornuate or septate uterus)

  • 2 prior fetal losses during the 2nd trimester


Overall risk of recurrence of fetal loss due to cervical insufficiency is probably 30%, leading to the question of how large a role fixed structural abnormalities have. Risk is greatest for women with 2 prior 2nd-trimester fetal losses.

Symptoms and Signs

Cervical insufficiency is often asymptomatic until premature delivery occurs. Some women have earlier symptoms, such as vaginal pressure, vaginal bleeding or spotting, nonspecific abdominal or lower back pain, or vaginal discharge.

The cervix may be soft, effaced, or dilated.


  • Transvaginal ultrasonography at ≥ 15 to 16 weeks for women with symptoms or risk factors

Usually, cervical insufficiency is not identified until after preterm delivery occurs for the first time.

The diagnosis of cervical insufficiency is suspected in women with risk factors or characteristic symptoms or signs. Then, transvaginal ultrasonography is done. Results are most accurate after 16 weeks gestation. Suggestive ultrasonographic findings include

  • Cervical shortening to < 2.5 cm

  • Cervical dilation

  • Protrusion of fetal membranes into the cervical canal


  • Cerclage

Cerclage (reinforcement of the cervical ring with nonabsorbable suture material) may be indicated based on history alone (history-indicated cerclage) or based on ultrasonographic findings plus history (ultrasound-indicated cerclage [1]). Cerclage appears to prevent preterm delivery in patients with 2 prior 2nd-trimester fetal losses.

For other patients, the procedure should probably be done only if all of the following are present:

  • Patients have a history that strongly suggests cervical insufficiency.

  • Cervical shortening is detected by ultrasonography before 22 to 24 weeks gestation.

  • Patients have a history of preterm deliveries.

Restricting cerclage to such patients does not appear to increase risk of preterm delivery and reduces the number of cerclages currently being done by two thirds. Evidence suggests that cerclage may help prevent preterm delivery in women who have a history of idiopathic preterm delivery and whose cervix is < 2.0 cm long.

If preterm labor is suspected after 22 to 23 weeks, corticosteroids (to accelerate fetal lung maturation) and modified activity (modified rest) may also be indicated (2).

Treatment references

  • 1. American College of Obstetricians and Gynecologists: ACOG Practice Bulletin No.142: Cerclage for the management of cervical insufficiency. Obstet Gynecol 123 (2 Pt 1):372–379, 2014. doi: 10.1097/

  • 2. Raju TN, Mercer BM, Burchfield DJ, Joseph GF Jr: Periviable birth: Executive summary of a joint workshop by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Academy of Pediatrics, and American College of Obstetricians and Gynecologists. Obstet Gynecol 123 (5):1083-1096, 2014. doi: 10.1097/AOG.0000000000000243.

Key Points

  • Usually, risk of cervical insufficiency cannot be predicted before premature delivery occurs for the first time.

  • Do transvaginal ultrasonography after 15 to 16 weeks if women have risk factors or symptoms.

  • Treat at-risk women with cerclage.

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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