SPTB and diabetes mellitus: The results indicated that there were differences in age (P < 0.001), pre-pregnancy BMI (P < 0.001), nulliparity (P = 0.045), pre-pregnancy diabetes (P < 0.001), pre-pregnancy hypertension (P = 0.001), and cervical incompetence (P < 0.001), between women with and without sPTB.