Model development
Quantitative data are expressed as the median
(interquartile range, IQR), and
qualitative data are expressed as the number (percentage). The
Wilcoxon-Mann-Whitney test or Fisher’s exact test was performed to
measure the distribution differences of variables between the
development and external validation groups.
Univariate and multivariate logistic
regression analysis was used to detect the correlation between clinical
variables and preterm birth at 28 weeks, 32 weeks, and 34 weeks by
applying a backward procedure based on the Akaike information criterion
(AIC). By drawing the ROC curve of the predicted probabilities of SPTB
before three gestational weeks(28, 32, 34 weeks) with multivariate
meaningful variables, the prediction power for SPTB before the three
gestational weeks was compared. Based on these results, a nomogram model
with higher predictive performance was established.