Background: The objective of the study was to verify whether ultrasound vaginal cervicometry, performed in the midtrimester of gestation, can effectively predict preterm delivery .This document is a guideline for effective use of transvaginal ultrasound in assessment of such risk. Material/Methods: 247 singleton pregnancies subdivided into 2 groups (group 1 = 53 cases and include the patient with cervical length < 3 cm and or funneling of the cervix was detected at the time of scanning and group2= 194 patients in which no risk factor regarding cervicometry was detected) were prospectively studied from the middle of gestation until delivery. In the 18th-20th week of gestation we performed ultrasound vaginal cervicometry to determine the length of the cervix, judge the shape of the internal os, and evaluate the cervix as normal or abnormal on the basis of these parameters. With the aid of one dimensional and multi-dimensional analysis, we tested the dependence of completed weeks of gestation and preterm delivery on the results of ultrasound cervicometry. Results: the preterm delivery was detected in 42 patients (79%) in group1 and was 8 patients (4.1) % in group2 with a statistically significant difference (p < 0.001). Conclusion: The implementation of ultrasound vaginal cervicometry at 18-20 weeks in the prenatal screening program can lead to effective and early detection of women with a significantly increased risk of preterm delivery.