Methods: A cohort analytical study enrolling 1,027 Thai pregnant women was carried out. Those who had risk factors of preterm labour, indicated preterm birth or the cases with fetal anomalies were not included. Nineteen parameters including cervical length at mid-trimester were assessed. The cutoff value for short cervix in this study was defined at less than 30 mm. Univariate and logistic regression analysis were used to determine the significance of each parameter.