Development and validation of a dynamic nomogram for SPTB at < 32 weeks
Based on meaningful independent factors in multivariate regression analysis, we developed a nomogram to predict the SPTB probability at < 32 weeks (Figure 2). Each point could be determined based on the intersection of the vertical line from the variable to the point axis. Then, the total risk score was calculated by adding each variable point. The possibility of twin SPTB at <32 weeks could be read on the total point axis.
Furthermore, a user-friendly dynamic predicative nomogram was established and available online(https://zhanwenqiang.shinyapps.io/DynNomapp/). The dynamic nomogram conveniently provided individual probability of SPTB which was calculated automatically by the input characteristics of each subject (Supplementary Figure 2). The Harrell’s concordance index value of the nomogram model in the training group was 0.856 (95%CI: 0.813-0.899). Calibration plots demonstrated that the nomogram was well calibrated, with favourable agreement between the nomogram-predicted probabilities and the actual probabilities of SPTB at <32 weeks (Supplementary Figure 3A). When applied to the external validation group, the Harrell’s concordance index value of the nomogram model in the external group was 0.808 (95%CI: 0.751-0.865). The calibration curves indicated that the probability predicted by the nomogram was in good agreement with the actual observation results (Supplementary Figure 3B).