Predictive value of cervical length for spontaneous preterm birth in women with cervical cerclage

Cervical cerclage is an important treatment used to prevent spontaneous preterm birth (sPTB), but it is not universally successful. Understanding the factors associated with cerclage treatment failure may lead to improved patient selection and better patient outcomes. The objective of this study was to investigate the value of pre- and post-cerclage cervical length (CL) in predicting sPTB < 34 weeks.

This was a retrospective cohort study conducted in four preterm birth prevention clinics in the UK. We included 331 women who had undergone cervical cerclage between January 2008 and March 2021, and analyzed their pre- and post-cerclage CL, as measured by transvaginal ultrasound scan. The primary outcome was sPTB < 34 weeks' gestation, assessed using multivariable logistic regression modeling (variables were pre- and post-cerclage CL, gestational age at cerclage and direction of CL change) and the generation of receiver-operating-characteristic (ROC) curves. Differences in sPTB for underlying risk factors (race, smoking history, previous cervical surgery or pregnancy history risk factors, including mid-trimester loss or sPTB) were assessed using Fisher's exact test.

Both pre- and post-cerclage CL were independently discriminative of sPTB < 34 weeks' gestation, with areas under the ROC curve of 0.635 (95% CI, 0.559-0.712) and 0.677 (95% CI, 0.604-0.751), respectively, and were modest contributors to sPTB prediction based on multivariable logistic regression modeling (odds ratio (OR), 0.964 (95% CI, 0.936-0.994), P = 0.018 and 0.940 (95% CI, 0.910-0.970), P < 0.001, respectively). There were no significant differences in the rate of sPTB < 34 weeks' gestation according to race, smoking history, previous cervical surgery or pregnancy history risk factors, including previous mid-trimester loss or sPTB.

Post-cerclage CL is the predominant predictor of sPTB < 34 weeks' gestation. Underlying sPTB risk factors (previous cervical surgery and pregnancy history) may influence pre-cerclage CL and the direction of CL change following cerclage, but once these are adjusted for, they do not influence the risk of sPTB < 34 weeks' gestation. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.