(Table 1)
Risk factors of preterm birth
In the univariate analysis, candidate variables with p-value < 0.1 (Table 1) were included in the multivariate binary logistic regression analysis. Overweight or obesity (OR:2.00, 95% CI:1.114-3.51 and OR:2.59, 95% CI:1.20-5.60, respectively), frequency of pregnancy ≥3 times (OR: 1.97, 95% CI:1.14-3.40), twin pregnancy (OR:4.52, 95% CI:2.40-8.51), IVF-ET(OR:2.24, 95% CI:1.19-4.19), gestational age of 1st short cervix (OR:0.953, 95% CI:0.910-0.999), cervical length (CL) of 1st short cervix (OR:0.908, 95% CI:0.86-0.96), history of preterm birth (OR:7.77, 95% CI:2.47-24.41), and autoimmune disease (OR:10.70, 95% CI:1.87-61.26) were found to be significant predictors of PTB < 37 weeks. Twin pregnancy (OR:3.08, 95% CI:1.80-5.29), gestational age of 1st short cervix (OR:0.90, 95% CI:0.86-0.94), CL of 1st short cervix (OR:0.88, 95% CI:0.84-0.93), history of preterm birth (OR:5.94, 95% CI:1.99-17.76), and prepregnancy hypertension (OR:4.66, 95% CI:1.75-12.45)were identified as significant predictors of PTB < 34 weeks. The results of the Hosmer-Lemeshow test were p=0.115 (χ2=12.92, df=8) and p=0.225 (χ2=9.048, df=8), respectively; and those of Omnibus test were p<0.001 (χ2=125.11, df=9) and p<0.001 (χ2=77.18, df=5), respectively, indicating good fit for the logistic regression models of PTB < 37 weeks and PTB < 34 weeks.