Cervical insufficiency (also known as cervical incompetence) is the presumed weakness of the cervix that leads to loss of an otherwise healthy pregnancy, usually in the second trimester. It is classically described as painful cervical dilation in the absence of vaginal bleeding, uterine contractions, or rupture of membranes.

The cause of cervical insufficiency is poorly understood. Risk factors include prior trauma to the cervix, including excisional procedures, mechanical dilation during dilation and curettage, and obstetrical lacerations.^1–4 Other risk factors include uterine anomalies,^5,6 in utero exposure to diethylstilbesterol (DES),⁷ and congenital anomalies including genetic disorders affecting collagen such as Ehler-Danlos syndrome.^8,9

The differential diagnosis for cervical insufficiency includes:

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  Preterm labor

  
  
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  Maternal or fetal infection

  
  
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  Placental abruption

  
  
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  Uterine distension (i.e. polyhydramnios, multiple fetal gestation)

Patients suffering from cervical insufficiency typically have mild symptoms such as pelvic pressure, menstrual cramping, backache, and increased vaginal discharge. Evaluation should include a detailed history to elicit symptoms and risk factors as well as a physical exam. The speculum exam should include evaluation of the cervical os, the presence or absence of prolapse fetal parts and membranes, and visualization of debris in the amniotic sac (Fig. 23-1) or overt purulent discharge. A number of studies have demonstrated that intraamniotic debris is associated with an underlying infection.^3,10 In addition, a digital exam to assess cervical dilation will be important to evaluate candidacy for an exam-indicated cerclage or the presence of active labor.

Laboratory evaluation is of limited use with the diagnosis, screening, or management of cervical insufficiency. Pregnancy is associated with a slight increase in the white blood cell (WBC) count, so unless this number is markedly elevated to the suggested infectious etiology, it is of limited value. Cervicovaginal fetal fibronectin is not indicated in this setting for diagnosis or management. When overt signs of intraamniotic infection are absent, amniocentesis can be considered to assist in the diagnosis and further management of the condition. Amniotic fluid should be evaluated for glucose level, gram stain, cell count, and culture.

Diagnosing cervical insufficiency is often challenging due to the lack of clear criteria and objective findings. In the absence of other causes, it is currently diagnosed by the presence of painless cervical dilation, with subsequent delivery in the second trimester.¹¹

There are four historical criteria as well:

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  Painless cervical dilation

  
  
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  Recurrent loss

  
  
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  Second-trimester births

  
  
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  Absence of other causes

The commonly used nonsurgical options include progesterone, vaginal pessary, and bedrest. However, some of these approaches, including bedrest, have not proved to be effective.^12,13 The primary surgical approach is the cervical cerclage. The standard methods include the Shirodkar and McDonald techniques. The superiority of one suture type or surgical technique over another has not been established.^12,14,15

In the McDonald procedure, a simple purse-string suture is inserted at the cervicovaginal junction,¹⁶ and studies have not demonstrated the benefit of the placement of an additional stitch for reinforcement.¹⁷ The Shirodkar technique involves the dissection of the vesicocervical mucosa to place the suture as close to the cervical internal os as possible. The bladder and rectum are dissected from the cervix in a cephalad manner, the suture is placed and tied, and mucosa is then replaced over the knot.¹⁸ The transabdominal approach is yet another option; it is reserved for patients in whom cerclage is indicated, but cannot be placed because of anatomic difficulties or in cases of a failed transvaginal cerclage.¹⁹

Indications in women with singleton pregnancies are as follows¹¹ (also see Table 23-1):

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  Cerclage

  
  
  
  
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    History-indicated (prophylactic) cerclage: History of one or more second-trimester pregnancy losses related to painless cervical dilation, and in the absence of labor or placental abruption. This type of cerclage is usually placed at 12 to 14 weeks of gestation.²⁰ Although the history-indicated cerclage can be considered after a second trimester loss, data from women with 1 or more prior preterm births (PTB) suggest that transvaginal ultrasound screening with cerclage placement if CL shortens is associated with similar perinatal outcomes as history-indicated cerclage. Therefore, the only adverse pregnancy history that has been, associated with benefit from history-indicated cerclage is a history of 3 or more PTBs or second-trimester losses.

    
    
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    Ultrasound-indicated cerclage: History of prior spontaneous preterm birth at <34 weeks of gestation and a short cervical length <25 mm before 24 weeks of gestation in the current pregnancy. The majority of women with suspected cervical insufficiency do not meet the criteria for a history-indicated cerclage. For these women, hydroxyprogesterone capropate is indicated if they have a prior preterm birth. Cervical monitoring with transvaginal ultrasound is also recommended starting at 16 weeks gestation.²¹ If cervical insufficiency is suspected, ultrasound surveillance may be started at 12 to 14 weeks gestation²¹ and is performed every 1 to 2 weeks until 24 weeks gestation. In general, since transvaginal ultrasound is widely used to assess cervical length, several studies have compared history-indicated cerclage vs. monitoring with serial ultrasound and ultrasound-indicated cerclage as needed. Conclusions from these studies are that at-risk women can be safely monitored with transvaginal ultrasound,^22,23 avoiding unnecessary cerclages in many of the women. The duration of surveillance should be from 16 to 24 weeks of gestation.²³

    
    
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    Physical exam–indicated cerclage (also known as emergency or rescue cerclage): The finding of painless cervical dilation upon exam in the second trimester,¹¹ after exclusion of labor or underlying infection. First, a clinical examination is necessary to rule out labor or infection. A cerclage may then be considered in those with singleton pregnancies who have dilation of the internal os when feasible. Women should be counseled about the potential maternal and perinatal morbidity, given the limited randomized controlled trials researching the procedure. Those with an intraamniotic infection will have a worse prognosis, and many consider performing an amniocentesis prior to cerclage placement to look for infection. The amniotic fluid is usually sent for Gram stain, WBC count, glucose, and culture for aerobic and anaerobic bacteria and mycoplasmas. Many practitioners will decide to perform an amniocentesis on a case-by-case basis when ultrasound and exam findings are consistent with inflammation. Examples of such cases include if the membranes are exposed at the external os, if there is debris (sludge) in the amniotic fluid, or if the dilation is greater than or equal to 2 cm. Perioperative antibiotics and indomethacin are usually administered with placement of exam-indicated cerclages.²⁴

  
  
  
  
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  Other nonsurgical interventions

  
  
  
  
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    Progesterone: In women with an incidentally detected short cervix without a history of preterm birth, cerclage is not indicated. However, vaginal progesterone is recommended as a management option. These women are asymptomatic, with an incidentally identified short cervical length ≤20 mm before 24 weeks of gestation.²⁵ See Chapter 45 on preterm labor for further discussion of treatment with progesterone.

    
    
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    Pessary: There has been an increased interest in the use of pessaries to prevent preterm birth, and multiple recent studies show conflicting results. Several small studies have evaluated the use of pessaries for prevention of preterm delivery in women with cervical insufficiency based on history.^26,27 In one study, Arabin et al (2003) reported cervical lengths of patients with prior spontaneous preterm birth before 36 weeks or early symptoms of preterm labor and twin pregnancies. Those with cervical lengths ≤15 mm were offered a pessary. Placement of a pessary was associated with an older gestational age at delivery in both twins and singletons.²⁸ In a multicenter randomized controlled trial of singleton pregnancies in women with a short cervix (<25 mm at 20 to 24 weeks), a cervical pessary did not result in a lower rate of spontaneous preterm delivery.²⁹ While one prospective randomized controlled trial supported the use of pessaries in twins with a short cervix (<25 mm),³⁰ another found no benefit in this group.³¹ Although the body of research does not support using a pessary to prolong gestation or improve neonatal outcomes, further study is indicated, as the current evidence is often limited by the difference in usage of progesterone among these trials. Currently, there is no cervical pessary that is approved by the US Food and Drug Administration (FDA) for the prevention of preterm birth or cervical shortening. In addition, the Arabin pessary is not approved for sale in the United States, and it should be used only as part of an ongoing clinical trial.³²

    
    
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    Bed rest: The use of bed rest for treatment of cervical insufficiency is discouraged. Although used historically, it has not been shown to be effective as a mode of treatment.^12,13