To establish the association between cervical consistency index (CCI) in the 11 to 13.6 weeks ultrasound screening and spontaneous preterm delivery before 35 weeks. Prospectively, CCI and cervical length were measured in a cohort of pregnant women who had been evaluated at routine first trimester scan for aneuploidy screening (11–13.6 weeks). The association between CCI, cervical length and subsequent preterm delivery before 35 weeks was evaluated. In addition we recorded maternal age, parity, weight, height and body mass index (BMI). Women who had spontaneous preterm delivery before 35 weeks were selected as cases. Pregnancies with fetal malformations were excluded. We evaluated 843 pregnant women and identified 23 cases (2.73%) with spontaneous preterm delivery below 35 weeks. No statistically significant differences were found in the variables: maternal age, parity, maternal weight, height, BMI between cases and controls. The CCI was lower in cases than in controls: mean 71.2% [range 67.3–77.6%] vs. 78.6% [range 72.4–84.5%](p <0.001), respectively. Cervical length did not differ between cases and controls: mean 37.2 mm [range 34–40 mm] vs. 39.1 mm [range 35–42 mm] (p = 0.14), respectively. Women who presented with preterm birth before 35 weeks had significantly lower values of CCI at first trimester than women who delivered at term. The measurement of CCI in ultrasound screening at 11–13.6 weeks may have clinical value for the early identification of women at risk of preterm birth before 35 weeks.