Maternal and obstetric factors associated with successful vaginal cerclage treatment: a prospective cohort study

To identify maternal and obstetric factors associated with cerclage effectiveness in preventing preterm birth (PTB) < 32 weeks, in order to subsequently develop a prediction model.

Patients with prior spontaneous PTB < 34 weeks and a singleton pregnancy who received a history-based or ultrasound-indicated cerclage were included. Main outcome was PTB < 32 weeks. Maternal and obstetric factors were included in multivariate logistic regression to compose weighted prediction models for PTB < 32 weeks, separately for both indications. Individual risk scores were calculated using the composed prediction models using the regression coefficients. Optimal cut-off values between high-, medium- and low-risk were determined using receiver operating characteristic curves.

222 patients received cerclage treatment. PTB < 32 weeks occurred in 43/222 (19.4%), of which in 13/85 (15.3%) in the history-based and 30/137 (21.9%) in the ultrasound-indicated group. Multivariate logistic regression was deemed unreliable in the history-based group. Following multivariate logistic regression in the ultrasound-indicated group, the prediction model included maternal age (p = 0.009), smoking (p = 0.004), gestational age at placement (p = 0.001) and cervical length (p = 0.004). We divided patients in high-, medium- and low-risk groups. PTB < 32 occurred in 12/15 (80.0%) in the high-risk, 11/50 (22.0%) in the medium-risk and 5/68 (7.4%) in the low-risk group.

Longer cervical length, higher maternal age, higher gestational age at placement and smoking status are associated with increased cerclage effectiveness. The prediction model effectively stratified included patients and can be a valuable tool in patient counselling. Future investigations should aim to include more variables and to externally validate the prediction model.