Is cerclage height associated with the incidence of preterm birth in women with an ultrasound-indicated cerclage?

OBJECTIVE: Our aim was to determine whether there was a cerclage height threshold associated with spontaneous preterm birth in patients with an ultrasound-indicated cerclage. STUDY DESIGN: We performed a retrospective cohort study of women with an ultrasound-indicated cerclage. Functional cervical length and the cerclage height (distance from cerclage to the external cervical os) were obtained. Our cohort was grouped into thirds, based on cerclage height percentile. Our primary outcome was spontaneous preterm birth less than 35 weeks. RESULTS: There were 20 women in group 1 (< 18 mm), 25 in group 2 (13-17 mm), and 25 in group 3 (>= 18 mm). Women with cerclage height 18 mm or greater had a lower incidence of spontaneous preterm birth less than 35 weeks (4%) when compared with those with a cerclage height less than 18 mm (33%) (relative risk, 0.69; 95% confidence interval, 0.55-0.86). CONCLUSION: Cerclage height of 18 mm or greater is associated with a reduction in spontaneous preterm birth for women with an ultrasound-indicated cerclage.