Development of a nomogram for estimating risk of imminent delivery using cervical elastography in pregnant women with short cervix

To develop a prediction model for estimating risk of imminent spontaneous preterm delivery (sPTD) using cervical elastography among women with short cervical length (CL) (≤25 mm). This prospective study was conducted by the Korean Research Group of Cervical Elastography (grant ID: HI18C1696). Women with short CL between 16 and 32 weeks of gestation were enrolled from June 2018 to December 2020 from 7 institutions. Cervical elastography using E-Cervix™ (WS80A, Samsung Medison, Seoul, Korea) was performed according to the standardised protocol previously suggested. Elastographic parameters were compared between term delivery group and preterm delivery (PTD) group. By the analysis of multivariable logistic regression and Cox proportional hazard model (Cox PH model), covariates were selected. On the basis of the predictive model with the identified risk factors a nomogram was constructed for predicting probability of sPTD and of being undelivered within 14- and 28-days. The accuracy of predicting model was evaluated using receiver operating characteristic curve analysis calculating the area under the curve (AUC) and external validation was performed. A total of 334 women were included. The prevalence of sPTD was 24.3% (81/334) and median gestational age at examination (GAE) was 24.6 weeks (16.1-32.0). The multivariable logistic regression and multivariable Cox PH model selected six independent predictors of sPTD through hierarchical modelling: twin pregnancy, GAE, CL, funnelling, IOS strain and mean strain. By adding the scores assigned on the points scale for each variable, the nomogram might determine the probability of sPTD and of pregnancy maintenance. The AUC of selected model to predict sPTD was 0.7658 and the AUC of delivery-free probability at 14- and 28-days after exam were 0.7770 and 0.8056. With external validation, the AUC of nomogram to predict sPTD was 0.6319. We confirmed that cervical elastography is a useful adjunctive tool to predict sPTD in women with short CL.