Objective: To evaluate the association between cervical length and the prediction of preterm birth at Hanoi Obstetrics and Gynecology Hospital from September 2024 to February 2025. Subjects and Methods: A prospective observational study was conducted on 120 pregnant women diagnosed with threatened preterm labor and admitted for inpatient treatment at Hanoi Obstetrics and Gynecology Hospital from September 2024 to February 2025. Results: The mean gestational age at admission was 30.2 ± 2.0 weeks, and the mean gestational age at delivery was 36.5 ± 3.0 weeks. A short cervical length (≤25 mm) was observed in 69.2% of cases, and 34.2% of patients showed cervical shape changes on transvaginal ultrasound. There was no significant association between cervical length and preterm birth within 7 days. However, a significant association was found between cervical length and preterm birth within 14 days. The group with cervical length ≤25 mm had a 16.4-fold increased risk of preterm birth within 14 days compared to the group with cervical length >25 mm. Conclusion: No significant association was found between cervical length and preterm birth within 7 days. However, a statistically significant association was found between cervical length and preterm birth within 14 days, with the group having cervical length ≤25 mm showing a 16.4- fold higher risk of preterm birth within 14 days compared to the group with cervical length >25 mm.