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Figure 1. Flowchart of study cohort.
Figure 2. Logistic regression models for predictors of PTB < 37 weeks and PTB < 34 weeks. PTB: preterm birth; BMI: body mass index; IVF-ET: in vitro fertilization and embryo transfer.
Figure 3. Profile of a nomogram to estimate risk of preterm birth < 37 weeks (A) and preterm birth < 34 weeks (B) in patients with a short cervix. Draw a line perpendicular from the corresponding axis of each risk factor until it reaches the top line labeled “Points”. Sum up the number of points for all risk factors then draw a line descending from the axis labeled “Total Points” until it intercepts the lower line to determine preterm birth probabilities. For binary variables, 0 = no and 1 = yes. For BMI before pregnancy categories, 0 = normal, 1 = overweight, 2 = obesity. Abbreviations: BMI = body mass index.
Figure 4. Validation of the nomogram. (A) The AUC of the models of PTB < 37 weeks and PTB < 34 weeks from observed data (nomogram) was 0.803 and 0.771, respectively. AUC=area under ROC. (B) Calibration curve for evaluating the agreement between the results and the predicted possibilities of PTB < 37 weeks. (C) Calibration curve for evaluating the agreement between the results and the predicted possibilities of PTB < 34 weeks.