Cervical insufficiency (CI), or cervical incompetence, occurs in 1 in 100 to 1 in 2000 gestations. Risk factors include prior cervical laceration, history of cervical conization, multiple terminations with mechanical cervical dilation, intrauterine diethylstilbestrol exposure, and congenital cervical anomaly.

The epidemiology is as imprecise as the various, sometimes controversial, criteria used to diagnose CI. One reasonable definition is painless cervical dilation during the second trimester in the absence of infection, placental abruption, uterine contractions, or uterine anomaly. Because CI is a diagnosis of exclusion, alternate diagnoses must be rigorously sought. Admittedly, diagnosis of CI and selection of patients for cervical cerclage can be difficult. Progesterone supplementation, pessary placement, and cervical cerclage have been suggested to prevent pregnancy loss from CI, but the evidence for their effectiveness is mixed. See chapter 6.

Patients may qualify for

• History-indicated cerclage: history of one or more prior second-trimester pregnancy losses in setting of painless dilation and absence of labor or abruption and typically placed at 12 to 14 weeks' gestation

• Ultrasound-indicated cerclage: cervical length less than 25 mm with a history of at least one preterm delivery, as assessed by serial ultrasounds from 16 to 24 weeks' gestation

• Rescue cerclage: patient with cervical dilation not suspected to be due to labor or abruption (see chapter 6,

  Table 6-1

  )

Vaginal cerclage may be performed by either using the McDonald or Shiradkor techniques. Permanent suture, either Prolene (polypropylene) or Mersiline (polyester fiber), is commonly employed. Prophylactic antibiotics and postoperative tocolytics have not been proven to affect outcome, except possibly in the case of rescue cerclage where such use is associated with a higher percentage of patients with pregnancies prolonged by at least 28 days.

• The risk of iatrogenic pregnancy loss ranges from 1% to 20% for elective cases. Rescue cerclage for CI/bulging membranes is associated with >50% risk of complications.

• An abdominal cerclage is placed at laparotomy or using minimally invasive (laparoscopic or robotic methods) techniques for women who have minimal to no residual cervical length (often due to large cone biopsies or trachelectomy) or who had prior pregnancy losses with a vaginal cerclage in situ. Subsequent cesarean delivery is necessary in the setting of an abdominal cerclage.

Progesterone supplementation, in the form of 17-hydroxyprogesterone caproate, is commonly prescribed to patients with a history of preterm delivery, whether caused by CI or not. Evidence has not proven an incremental benefit to this treatment when added to cerclage. Vaginal progesterone may be employed for treatment of patients with cervical shortening in the absence of history of preterm birth.

Vaginal pessaries are designed to transfer the weight of uterine contents away from the cervix, and by changing the axis of the cervical canal. The best studied pessaries for CI are the Arabin design. In meta-analyses of randomized controlled trials among singleton pregnancies with pessaries placed for cervical shortening without history of preterm delivery, pessaries were not shown to provide a significant benefit. Data from twin gestations, an area in which cerclage has been shown to be ineffective, have been more promising. Further research is needed to understand the optimal use of pessaries in current obstetric practice; currently, their use may be considered reasonable for twin gestations and for cervical shortening in singleton gestations for patients without history of preterm delivery.