A multivariable model to guide the decision for pessary placement to prevent preterm birth in women with a multiple pregnancy : a secondary analysis of the ProTWIN trial

OBJECTIVE: The ProTWIN Trial (NTR1858) showed that in women with a multiple pregnancy and a cervical length less than the 25(th) percentile (38mm), prophylactic use of a cervical pessary reduced the risk of adverse perinatal outcome. We investigated whether other maternal or pregnancy characteristics collected at baseline can improve identification of women with the most probable benefit from pessary placement. METHODS: ProTWIN is a multicenter randomized trial in which 808 women with a multiple pregnancy were assigned to pessary or control. Using this data we developed a multivariable logistic model comprising treatment, cervical length, chorionicity, pregnancy history and number of fetuses and the interaction of these variables with treatment as predictors of adverse perinatal outcome. RESULTS: Short cervix, monochorionicity and nulliparity were predictive factors for a benefit from pessary insertion. History of previous preterm birth and triplet pregnancy were predictive factors of possible harm from pessary. The model identified 35% of women as benefiting (95% CI: 32% to 39%), which is 10% more than using cervical length only (25%) for pessary decisions. The model had acceptable calibration. We estimated that using the model to guide the choice of pessary would reduce the risk of adverse perinatal outcomes significantly from 13.5% when no pessary is inserted to 8.1% (absolute risk reduction 5.4%, 95% CI: 2.1% to 8.6%). CONCLUSIONS: We developed and internally validated a multivariable treatment selection rule, with cervical length, chorionicity, pregnancy history and number of fetuses. If externally validated, it can be used to identify women with a twin pregnancy who benefit from a pessary, and therefore a reduction in adverse perinatal outcomes in twin pregnancies can be anticipated