The effect of therapeutic McDonald cerclage on cervical length as assessed by transvaginal ultrasonography

OBJECTIVE: Our goal was to study the effect of therapeutic McDonald cerclage on cervical length with the use of transvaginal ultrasonography. STUDY DESIGN: Cervical length was measured serially in singleton pregnancies in which there were doubts regarding cervical competence. When shortening of the cervix was substantial before 27 weeks' gestation a McDonald cerclage was applied. Wilcoxon signed rank test was used, and 1-tailed P < .05 was considered significant. RESULTS: In the 34 pregnancies studied, the mean cervical length measured at a mean gestational age of 14 weeks had decreased significantly (P < .0001) from 42 mm (95% confidence interval 38-47) to 21 mm (95% confidence interval 19-23) at a mean gestational age of 20 weeks 5 days, when a cerclage was applied. After the cerclage the mean cervical length increased significantly (P < .0001) to 34 mm (95% confidence interval 30-38) at a mean gestational age of 22 weeks 1 day (95% confidence interval 21 weeks 1 day-23 weeks 2 days). CONCLUSIONS: Therapeutic McDonald cerclage results in a longer cervical length as measured by transvaginal ultrasonography.