Population characteristics
Among pregnant women enrolled in this study, data of 555 women with a short cervix were used to analyze the risk factors of PTB < 37 weeks and 538 were used to identify the predictors of PTB < 34 weeks.(Figure 1) Overall, 187/555 (33.7%) women had PTB < 37 weeks and 91/538 (16.9%) patients had PTB < 34 weeks. The gestational age of short cervix at the first time ranged from 11 to 35 weeks among patients who had PTB < 37 weeks and from 11 to 33 weeks among patients who had PTB < 34 weeks.