Background: To assess the association between cervical length (CL) and uterine artery (UtA) Doppler screening at the second trimester with spontaneous preterm birth. Materials and Methods: In this case-control study, 162 antenatal women were recruited, among whom 82 women were admitted with preterm labor (case group) and 80 women only received routine antenatal care (control group). After the pulsatility index (PI), resistance index (RI), and CL were measured using transvaginal sonography at 24 weeks of pregnancy, the distribution values of these variables in patients with idiopathic preterm delivery before 37 weeks were compared to those of patients with delivery at or after 37 weeks. Results: The present results showed that in the case group (p = 0.035), PI values were 1.64 and 1.42 for term and preterm births, while in the control group (p = 0.543), PI values were 1.71 and 1.85 for term and preterm births, respectively. Furthermore, mean PI (MPI) values of the case and control groups were 1.43 and 1.73 (p = 0.007), respectively. The present findings also indicated that in the case group (p = 0.081), CL values were 26.73 and 23.65 for term and preterm births, while in the control group (p = 0.644), CL values were 28.33 and 29.3 for term and preterm births, respectively. In addition, mean CL values of the case and control groups were 23.45 and 28.48 (p = 0.001), respectively. Conclusion: Although UtA Doppler screening at the second trimester can provide nearly estimates of spontaneous birth, the maternal demographic characteristics and previous obstetrics history are important variables to consider when predicting the likelihood of complications in pregnancy.