Cerclage in cervical insufficiency: when and to whom?

Surgical treatment for cervical insufficiency is cervical cerclage, widely used since McDonald and Shirodkar independently introduced their techniques 50 years ago. Another alternative is expectant management. Most of the randomised trials comparing the efficacy of cerclage versus expectant management have found no significant improvement in preterm birth and neonatal morbidity among women treated with cerclage (1 3). Therefore, justified questions are: should cerclage be used at all? and, if so, when and to whom? To answer the questions, one should be aware of the variations in the definition and diagnostic criteria of cervical insufficiency, as well as of the heterogeneity of randomised trials, and the inconsistency of their results. Cervical insufficiency is a well-recognised cause of preterm birth. The frequency of its occurrence remains unclear. Historically, cervical insufficiency or incompetence was defined as an inability of the uterine cervix to retain pregnancy to term. The diagnosis was based on the history of painless cervical dilation and pregnancy loss during the second or early third trimester of pregnancy, and on the presence of risk factors, such as past surgical trauma to the cervix or congenital anomaly. The condition was believed to re-occur in all subsequent pregnancies. Since the advent of transvaginal ultrasonography in 1990s, major attention in the diagnosis of cervical insufficiency was moved from the history to the assessment of cervical length and function by ultrasound (4). Cervical function is now viewed as a continuous variable which is affected by different factors, and expressed in different degrees in subsequent pregnancies. A short cervix with or without funnelling has been adopted as a marker of cervical insufficiency. However, there is no agreement on the thresholds for a short cervix and funnelling. So, what is the proper treatment if even the diagnostic criteria are variable? Again, the question is difficult to answer. For decades, women in whom the diagnosis of cervical insufficiency was based on history and the presence of risk factors were treated with prophylactic (elective) cerclage, placed at the end of the first trimester in subsequent pregnancies. Many observational studies lent support to this practice. In contrast, recent randomised trials on prophylactic cerclage based on historical features alone have failed to show a clear benefit in most women. This indicates that most women with a history consistent with traditional diagnosis of cervical insufficiency do not have recurrent pregnancy loss, and that more than half of prophylactic cerclage procedures have been unnecessary (5). Only a subgroup of women with a history of 3 or more mid-trimester pregnancy losses or early preterm deliveries were shown to benefit from this intervention (delivery before 33 weeks of gestation, 15% in the cerclage group versus 32% in the control group) (6). Prophylactic cerclage is recommended to be placed at 13 16 weeks’ gestation. Other women with a high risk by history should be followed by serial transvaginal cervical ultrasound, beginning between 16 and 20 weeks of gestation. If serial ultrasound measurements reveal a short cervix or progressive shortening in the cervical length, other potential causes of cervical changes (uterine contractions, fetal anomalies, decidual hemorrhage, intrauterine infections) should be ruled out before urgent/therapeutic cerclage can be considered. However, randomised trials on the effectiveness of urgent cerclage show controversial results (2,3). Thus, even if other causes of cervical shortening have been ruled out, the decision to place an urgent cerclage should be made with caution. Expectant management is recommended in the first line if a short cervix is identified after fetal viability has been achieved. Acta Obstetricia et Gynecologica. 2007; 86: 387 388