Does the rate of cervical shortening after cerclage predict preterm birth?

Objective: The objective of this study is to evaluate whether the rate of cervical shortening after cerclage can predict spontaneous preterm birth (SPTB).Methods: Women who had cervical length (CL) assessments after cerclage placement were identified. The rate of cervical shortening and its relationship with SPTB was established using a generalized linear regression model. Secondary outcomes included relationship between cervical shortening and risk of SPTB in those with a post-cerclage CL <25 mm versus ≥25 mm at 18-20 weeks; and the rate of cervical shortening in women who delivered preterm compared with those who delivered at term.Results: One hundred thirty-four patients were included and 30 (22.4%) delivered at <36 weeks. A rate of cervical shortening of 1 mm/week conferred a risk of SPTB of 22%. Among women with cerclage who had a CL <25 mm at 18-20 weeks, 1 mm/week of cervical shortening was associated with a 59% risk of SPTB. Patients with cerclage who delivered at term had a slower rate of cervical shortening compared to those who delivered preterm (0.62 mm versus 1.40 mm per week, p = 0.008).Conclusions: The rate of cervical shortening after cerclage placement is associated with the risk of SPTB. Sonographic surveillance of the rate of cervical shortening may be useful in assessing risk for SPTB in patients with cerclage.