Throughout the natural course of pregnancy, the cervix remains long, thick and firm until the late third trimester when it slowly begins to soften, dilate and efface to eventually allow the passage of a fetus. The inability of a cervix to maintain its integrity prior to that time can result in miscarriage or preterm birth. When this occurs in the absence of clinical signs or symptoms of labor, it is referred to as cervical insufficiency or incompetence. In the past, nonsurgical approaches such as activity restriction and pelvic rest have been suggested, though their use has not proven effective and should be discouraged. Cervical cerclage is a surgical procedure that can be performed in an attempt to maintain the structural integrity of the cervix in order to prolong gestation and improve obstetrical outcomes.
The pathophysiology behind cervical insufficiency is still not well understood but is thought to arise from a structural or functional defect of the cervix. Risk factors include any prior cervical procedures or trauma, including loop electrode excisional procedure, cone biopsy, prior cervical lacerations, and repetitive cervical dilation and/or pregnancy terminations. Other possible etiologies include maternal connective tissue diseases or abnormalities, congenital Mullerian anomalies, or maternal exposure in utero to diethylstilbestrol.
There are three well-accepted indications for cervical cerclage placement. According to the American College of Obstetricians and Gynecologists (ACOG), a history-indicated or prophylactic cerclage may be placed when there is a “history of one or more second-trimester pregnancy losses related to painless cervical dilation and in the absence of labor or abruptio placentae,” or if the woman had a prior cerclage placed due to cervical insufficiency in the second trimester.
An ultrasound-indicated cerclage may be considered for women who have a history of spontaneous loss or preterm birth at less than 34 weeks gestation if the cervical length in a current singleton pregnancy is noted to be less than 25 mm before 24 weeks of gestation. It is important to note that this recommendation is invalidated without the history of preterm birth.
Physical examination-indicated cerclage (also known as emergency or rescue cerclage) should be considered for patients with a singleton pregnancy at less than 24 weeks gestation with advanced cervical dilation in the absence of contractions, intraamniotic infection or placental abruption.
While ACOG does not list any absolute contraindications, special attention should be given to the considerations listed above. Additionally, cerclage is not recommended in pregnancies of multiple gestations.
The most common technique for performing transvaginal cervical cerclage is the McDonald method. First applied in 1951, this procedure involves a simple purse-string suture at the cervicovaginal junction. Under regional anesthesia, the patient is placed in the dorsal lithotomy position and prepped with a vaginal betadine solution. A speculum or right-angle retractors are used to adequately visualize the cervix. The anterior lip of the cervix may be gently grasped using ring polyp forceps, and the vesicocervical junction should be identified. Just anterior to this junction, a nonabsorbable suture is inserted into the cervix in a purse-string manner, taking caution to avoid the paracervical vessels. The suture is then tied down with a surgeon knot, either anterior or posterior.
The Shirodkar technique begins with the patient positioned and prepared in the same manner. Once the vesicocervical reflection has been identified, the mucosa of the anterior cervix is incised at this junction, similar to a vaginal hysterectomy. An Allis clamp can be used to elevate the bladder flap while the bladder is then mobilized cephalad using blunt or sharp dissection. This is continued until reaching the level of the internal cervical os. A similar incision is then made in the posterior cervical mucosa. Again, an Allis clamp can be used for traction on the posterior mucosa, while the reflection of the Pouch of Douglas is created using blunt dissection. An Allis clamp can then be applied at the 9 o’clock position to retract and isolate the paracervical vessels. A nonabsorbable suture can then be passed from anterior to posterior just beneath the Allis clamp so as not to enter the cervical os. The Allis should then be removed and placed in a similar fashion at the 3 o’clock position. The suture can then be passed from posterior to anterior, with special attention to lay the suture flat against the posterior aspect of the cervix. The suture can then be securely tied anteriorly. The anterior and posterior mucosa can then each be reapproximated in order to bury the cerclage stitch. This may be done in the running or interrupted fashion using an absorbable suture. The free ends of the cerclage stitch may be left exposed to facilitate subsequent removal.
Both ultrasound-indicated and physical examination-indicated cerclages should be placed prior to 24 weeks gestation. Women undergoing a history-indicated cerclage procedure should have placement between 12-14 weeks gestation. There have been no proven clinical benefits to routine post-cerclage cervical length surveillance. Studies have demonstrated the comparative efficacy of McDonald and Shirodkar techniques. Thus, due to relative ease of placement and removal of the McDonald cerclage, that technique tends to be used more frequently. There is also a consideration for abdominal cerclage placement for women who have failed a previous transvaginal cerclage.
Cervical cerclages should be removed between 36-38 weeks of gestation, prior to the onset of labor. Removal can safely be performed in the office setting. If preterm labor is suspected or diagnosed, cerclage should be removed at that time to minimize potential trauma to the cervix. If a cesarean is planned, removal may be delayed until the time of surgery.
This procedure is not without risk, but the ultrasound-indicated and physical examination-indicated cerclages likely incur more risk than history-indicated cerclages. Risks include infection or sepsis, inadvertent rupture of membranes, lacerations at the surgical site, and anesthesia-related complications. Recent reviews suggest that initial dilation greater than 4cm is associated with a poor prognosis. These risks must be weighed against the benefit of the structural support of the cervix.
Preterm birth is a major cause of neonatal morbidity and mortality. One of the most significant risk factors for preterm birth is a history of preterm delivery, and one etiology of preterm birth is cervical insufficiency. Cervical cerclages have been used to prevent preterm birth since the 1950s, yet their efficacy continues to be questioned and studied. A 2017 Cochrane review supports that “pregnant women with cerclage were less likely to have preterm births compared to controls before 37, 34, and 28 completed weeks of gestation.” However, outcomes may vary based on indication for cerclage.
A meta-analysis showed that patients undergoing elective cerclage delivered at a significantly higher gestational age and had significantly higher birth weights compared to those undergoing emergency cerclage. Additionally, there was a higher incidence of premature rupture of membranes in the emergency cerclage group. While each patient and situation deserves its own individual consideration, cervical cerclage should remain an instrument for the indications described above.
Cervical cerclage is a common obstetric procedure performed in an attempt to improve cervical integrity, prolong gestation, and prevent preterm birth. A cerclage may be indicated by history, ultrasound findings, or physical exam. They should be performed by a skilled obstetrician for the indications described above. Through a combined effort of the patient in obtaining early prenatal care, the radiologist in taking careful cervical length measurements, and the obstetrician in conducting a thorough history and physical exam, it is possible that neonatal morbidity and mortality can be reduced via cerclage placement in select populations.
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