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.
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
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
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 ). Cerclage appears to prevent preterm delivery in patients with ≥ 2 prior 2nd-trimester fetal losses. In these patients and other patients at high risk of cervical insufficiency, cerclage is done during the 1st trimester. Cerclage may be done before 24 weeks if the patient's obstetric history is unknown but problems are suspected and the patient has a short cervix.
For other patients, the procedure should probably be done only if all of the following are present:
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).
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: 10.1097/01.AOG.0000443276.68274.cc
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