Background: Cervical length measurement is still the most widely used method to predict preterm labor. Recent studies have reported that in addition to cervical length, uterocervical angle (UCA) may also be useful in predicting preterm labor. The main purpose of this study was to evaluate the use of the anterior UCA to predict preterm labor in symptomatic pregnant women with a cervical length of 20 to 30 mm. Methods: In this prospective cohort study, 48 patients with a cervical length of 20 to 30 mm who applied to the emergency department with any preterm labor symptoms, between September 2019 and February 2020, were included as the study group. Cervical length and anterior UCA were measured at the first admission. Of these 48 patients, 12 patients who gave birth before 37 weeks were called the ‘preterm labor group’, and 36 patients who gave birth at 37 weeks or later were named the ‘preterm threatened but delivered at term’ group. The control group consisted of 46 healthy pregnant women who were matched with the study group in terms of age, body mass index (BMI), and the gestational week at which anterior UCA was measured. The three groups were compared in terms of anterior UCA values. Results: The cervical lengths of the ‘preterm labor’ and ‘preterm threatened but delivery at term’ groups were similar and shorter than the control group (25.4 mm, 25.1 mm, and 35 mm, respectively, p 0.001). Anterior UCA value in the ‘preterm labor’ group (116.1) was found to be significantly higher than both ‘preterm threatened but delivered at the term’ group (100.2) and the control group (98.6) (p = 0.001). Receiver operating curve (ROC) analysis was performed to determine a threshold value of anterior UCA that could predict preterm labor in symptomatic pregnant women with a cervical length of 20 to 30 mm. Area under curve (AUC) analysis of anterior UCA for estimation of preterm labor was 0.647 (p = 0.014, 95% confidence interval (CI) = 0.52–0.77). According to this analysis, the threshold value of anterior UCA was determined as 95.3, with 72% sensitivity, and 63% specificity. Conclusion: The anterior UCA can be used to better predict preterm labor in symptomatic pregnant women with a cervical length of 20 to 30 mm without cervical effacement and dilation.