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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) or use of vaginal progesterone.
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 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)
≥ 3 prior fetal losses during the 2nd trimester
Usually, cervical insufficiency is not identified until after preterm delivery occurs for the first time.
The diagnosis is suspected in women with risk factors or characteristic symptoms or signs. Then, transvaginal ultrasonography is done. Results are most accurate after 16 wk gestation. Suggestive ultrasonographic findings include cervical shortening to < 2.5 cm, cervical dilation, and protrusion of fetal membranes into the cervical canal.
Ultrasonography of women without symptoms or risk factors is not recommended because results do not accurately predict preterm delivery.
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 ≥ 3 prior 2nd-trimester fetal losses. For other patients, the procedure should probably be done only if they have a history that strongly suggests cervical insufficiency and if cervical shortening is detected by ultrasonography before 22 to 24 wk gestation; 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. Recent 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.
Vaginal progesterone (200 mg every night) can reduce risk of preterm delivery in certain women. It can be offered to women who have a history of idiopathic prior preterm delivery or cervical shortening (detected by ultrasonography) in the current pregnancy, particularly women who do not meet the criteria for cerclage. Whether vaginal progesterone further reduces risk in women treated with cerclage is unclear.
If preterm labor is suspected after 22 to 23 wk, corticosteroids (to accelerate fetal lung maturation) and modified rest may also be indicated.
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