Gradual, painless dilation of the cervix during pregnancy, leading to recurrent inability to maintain pregnancy beyond the second trimester. Cervical dilation occurs in the absence of clinical contractions and/or labor. Diagnosis is clinical.

Incompetent cervix

Shortened cervix

Preterm birth syndrome

• Painless cervical dilation during the second trimester
• Nonspecific presentation: Backache, pelvic pressure, contractions, vaginal spotting, vaginal discharge

Most cases are either idiopathic or iatrogenic as a result of prior cervical surgery. The cause is thought to be a loss of elastic fibers in the cervices of affected women.

• Preterm labor
• Shortened cervix

• Prior obstetric history, particularly with regard to previous preterm deliveries or spontaneous abortions
• Prior history of any gynecologic procedures, especially those involving the cervix
• Serial digital cervical examinations
• Serial transvaginal ultrasound

Amniocentesis with analysis for white blood cell count, glucose, Gram stain, and culture: Abnormal results for any of these markers may indicate a subclinical infection, which increases risk for preterm birth. Abnormalities may help in selecting patients who would benefit from emergent cerclage, although this benefit should be weighed against the inherent risks of amniocentesis.

Transvaginal ultrasound: Cervical shortening on ultrasound may be a diagnostic marker for cervical insufficiency.

Cerclage has long been the mainstay of treatment for cervical insufficiency (Fig. E1 to E3 to ). However, randomized controlled trials (RCTs) comparing the rates of preterm birth in patients receiving cervical cerclage vs. those without cerclage have produced conflicting results, with many studies showing little or no improvement in preterm birth rates. The greatest benefit of cerclage is in women with singleton pregnancies who have experienced a previous preterm birth, and cerclage is actually detrimental to women carrying multiple gestations. The most common risk associated with cerclage is cervical laceration during delivery (1% to 13%). Bed rest is often used when there is a threat of preterm birth, although its benefit is not proven and it has detrimental effects for the mother, such as venous thromboembolic events; thus it is not recommended.

Ultrasound-indicated cerclage should be placed in women with ultrasonographic evidence of cervical shortening (<25 mm) before 24 wk gestation and a history of a preterm birth before 34 wk. Women who present with painless cervical dilation in the second trimester may be candidates for a physical-examination-indicated cerclage (rescue cerclage) after being ruled out for uterine activity and evidence of infection. Data are limited on the efficacy of placing a physical-examination-indicated cerclage. Women should be counseled about the potential risks of rescue cerclage in the setting of unclear benefit. Placement of a cervical pessary is only currently recommended in the setting of research trial protocols.

Prophylactic cerclage (history-indicated cerclage) has been shown by several studies and meta-analyses to be most heavily indicated in women with prior history of multiple preterm births. Women with a history of one or more second-trimester deliveries with no symptoms or signs of labor at the time of the delivery may be candidates for a prophylactic cerclage, placed at 13 to 14 wk gestation. Women with this history should also be offered 17-OH progesterone injections between 16 and 36 wk.

Patients with a singleton pregnancy, prior history of preterm birth, and shortened cervix (<25 mm) on transvaginal ultrasound should be counseled regarding amniocentesis and cerclage placement.

Patients at risk of preterm labor should be referred to maternal-fetal medicine.

Cervical Incompetence (Patient Information)

Preterm Labor (Related Key Topic)

Premature Rupture of the Membranes (Related Key Topic)