Effectiveness of Cerclage According to Severity of Cervical Length Shortening: A Meta-Analysis

A finding of a short cervical length (CL) during the second trimester on transvaginal ultrasound predicts preterm birth. Previous data from a meta-analysis and a large trial have shown that cerclage prevents preterm birth in singleton women with a previous preterm birth, once a short cervix has been detected on ultrasound imaging. Because the CL at which cerclage was performed varied between ≤15 mm and <25 mm in these studies, it is unclear whether the efficacy of ultrasound-indicated cerclage depends on the degree of cervical shortening. Some investigators have suggested that cerclage may not be very effective for the very short (<6 mm) or mildly shortened (15-24 mm) cervix. The present study estimated the effectiveness of cerclage in women with different degrees of CL shortening. The data were obtained from a meta-analysis of 4 randomized trials evaluating the use of cerclage in singleton women with a CL <25 mm on second-trimester transvaginal ultrasound imaging. A total of 208 women who had a previous preterm birth and 344 who had no such history were randomized to cerclage or no cerclage. The efficacy of ultrasound-indicated cerclage in preventing the primary outcome of preterm birth <35 weeks was evaluated in women with different degrees of cervical shortening. In women with both a previous preterm birth and CL <25 mm, cerclage resulted in a significant reduction in preterm birth <35 weeks; the relative risk was 0.61, with a 95% confidence interval of 0.40 to 0.92. Cerclage also resulted in a significant reduction in preterm birth <37 weeks for CL ≤5.9 mm, ≤15.9 mm, 16 to 24.9 mm, and <25 mm. For women without a previous preterm birth, cerclage did not decrease the risk of preterm birth for any CL. These findings suggest that ultrasound-indicated cerclage has similar effectiveness for reducing preterm birth among singleton women with a previous preterm birth and CL <25 mm, regardless of the degree of CL shortening.