The inability of the uterine cervix to retain a pregnancy in the absence of the signs and symptoms of clinical contractions, or labor, or both in the second trimester is referred to as cervical insufficiency.
Despite having been part of obstetric practice for over a century, both the role of cervical cerclage and indications for it remain ill- defined and controversial, with wide practice variations in different clinical settings. In part, the lack of clarity that surrounds cerclage is fostered by uncertainty in identifying those patients who will truly benefit from its use (i.e., those with true cervical insufficiency or truly increased risk of early preterm delivery).
The pathophysiology of cervical insufficiency is still poorly understood. Factors that may increase the risk of cervical insufficiency include surgical trauma to the cervix from conization, loop electrosurgical excision procedures, mechanical dilation of the cervix during pregnancy termination, or obstetric lacerations, although data confirming these associations are inconsistent. In many cases, especially when clinical features and findings lead to suspicion of the diagnosis in the first pregnancy, these risk factors may not be present and the cause may remain idiopathic.
The diagnosis of cervical insufficiency is challenging because of a lack of objective findings and clear diagnostic criteria. Diagnosis is based on a history of painless cervical dilation after the first trimester with subsequent expulsion of the pregnancy in the second trimester, typically before 24 weeks of gestation, without contractions or labor and in the absence of other clear pathology (e.g., bleeding, infection, ruptured membranes). It should be noted, however, that although in some situations there may be a continuum between cervical insufficiency and preterm labour and delivery, in others these are distinct and unrelated processes. A history of preterm labour or the identification of factors that increase the risk for preterm birth do not always necessarily indicate risk for cervical insufficiency.
Transvaginal ultrasonography has been increasingly used as a demonstrably valid and reproducible method of cervical assessment, and cervical shortening correlates with the risk of preterm delivery. Cervical length assessment by ultrasound is an established means of assessing the risk for preterm labour and delivery (cervical length < 25 mm). Patients may also be found to have cervical dilatation rather than just shortening, or they may present with preterm membrane rupture. Recently, attempts have been made to use assessment of cervical length in the second trimester and the identification of cervical shortening as an ultrasonographic diagnostic marker of cervical insufficiency. However, short cervical length has been shown to be a marker of preterm birth in general rather than a specific marker of cervical insufficiency. Nonetheless, cerclage may be effective in particular circumstances when a short cervix is found.
There is no diagnostic test for cervical insufficiency. Although many tests have been suggested including, hysterosalpingography and radiographic imaging of balloon traction on the cervix, assessment of the ease of insertion of cervical dilators without resistance, the use of a balloon elastance test, and use of graduated cervical dilators to calculate a cervical resistance index. However, none of these meet the criteria required for a diagnostic test and they should not be used to diagnose cervical insufficiency.
Without a reliable diagnostic test, it becomes necessary to screen for or to predict the likelihood of cervical insufficiency. This process is based upon the identification and recognition of key risk factors in the woman’s history and in the index pregnancy.
The most common factor in the patient history that indicate she may be at risk, is a prior second trimester pregnancy loss related to painless cervical dilation and in the absence of labor or abruptio placentae. Cerclage placement may be indicated based on a history of cervical insufficiency, physical examination findings, or a history of preterm birth and certain ultrasonographic findings. The safety and efficacy of cerclage in the treatment of patients with cervical insufficiency after fetal viability have not been adequately assessed. Cerclage should be limited to pregnancies in the second trimester before fetal viability has been achieved.
According to the American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin “Cerclage for Cervical Insufficiency” (February 2014), following are the indications for Cervical Cerclage in Women With Singleton Pregnancies :
History of one or more second-trimester pregnancy losses related to painless cervical dilation and in the absence of labor or abruptio placentae
Prior cerclage due to painless cervical dilation in the second trimester
Painless cervical dilation in the second trimester (after clinical examination rules out uterine activity, or intraamniotic infection, or both)
Ultrasonographic Finding With a History of Prior Preterm Birth
Current singleton pregnancy, prior spontaneous preterm birth at less than 34 weeks of gestation, and short cervical length (less than 25 mm) before 24 weeks of gestation
ACOG mentions the following in it’s Practice Bulletin “Cerclage for Cervical Insufficiency” (February 2014),
“Although women with a current singleton pregnancy, prior spontaneous preterm birth at less than 34 weeks of gestation, and short cervical length (less than 25 mm) before 24 weeks of gestation do not meet the diagnostic criteria for cervical insufficiency, available evidence suggests that cerclage placement may be effective in this setting. Cerclage is associated with significant decreases in preterm birth outcomes, as well as improvements in composite neonatal morbidity and mortality, and may be considered in women with this combination of history and ultrasonographic findings.”
What are the Surgical approaches to treat cervical insufficiency?
Surgical approaches to treat cervical insufficiency include, transvaginal and transabdominal cervical cerclage.
The standard transvaginal cerclage methods currently used include modifications of the McDonald and Shirodkar techniques. The superiority of one suture type or surgical technique over another has not been established.
Transabdominal cervicoisthmic cerclage generally is reserved for patients in whom cerclage is indicated based on the diagnosis of cervical insufficiency but cannot be placed because of anatomical limitations (e.g., after a trachelectomy), or in the case of failed transvaginal cervical cerclage procedures that resulted in second- trimester pregnancy loss. Transabdominal cerclage can be accomplished through open laparotomy or operative laparoscopy depending on physician experience, or patient preference. No evidence exists to suggest that one surgical approach for cervicoisthmic cerclage placement has an advantage over the other techniques. Abdominal cerclage procedures usually are performed in the late first trimester or early second trimester (10–14 weeks of gestation) or in the nonpregnant state. The stitch can be left in place between pregnancies with subsequent cesarean delivery.
Is cerclage placement associated with an increase in morbidity?
Overall, there is a low risk of complications with cerclage placement.
Reported complications include rupture of membranes, chorioamnionitis, cervical lacerations, and suture displacement. The incidence of complications varies widely in relation to the timing and indications for the cerclage. A cerclage in the presence of membrane rupture or dilation generally is associated with an increased risk of complications. Life-threatening complications of uterine rupture and maternal septicemia are extremely rare but have been reported with all types of cerclage.
Compared with transvaginal cerclage, transabdominal cerclage carries a much greater risk of hemorrhage, which can be life threatening, in addition to all the other complications associated with abdominal surgery. Furthermore, it generally precludes the performance of uterine evacuation or vaginal delivery. However, transabdominal cerclage is not an indication for otherwise non-indicated delivery before 39 weeks of gestation.