Reference range of the weekly uterine cervical length at 8 to 38 weeks of gestation in the center of Iran

BACKGROUND: There is an inverse relation between the uterine cervical length during pregnancy and the frequency of preterm delivery. The purpose of this study was to construct a chart and evaluate the cervical length at 8 to 38 weeks of normal gestation in the center of Iran. MATERIALS AND METHODS: Uterine cervical length was measured on 930 asymptomatic pregnant women by abdominal ultrasonographic technique. For statistical evaluation, regression analysis and calculation of percentiles were performed. RESULTS: Our data show a significant decrease in uterine cervical length with increasing gestational age. The mean uterine cervical length exhibits minimal changes from 10 to 24 weeks for most women in this study, although the shortening is more prominent at 33 to 38 weeks’ gestation. The mean shortening of the uterine cervical length between the second and the ninth months was 14.82% (P < 0.05). Also, the cervical length means in trimesters 1, 2 and 3 were 39.30 ± 4.33, 38.28 ± 5.13 and 36.58 ± 4.58 mm, respectively. The third trimester showed a significant reduction (P < 0.05) in cervical length compared to the first and second trimesters (6.92% and 4.44%, respectively). New charts with the 5(th), 10(th), 50(th), 90(th), and 95(th) percentile are presented. CONCLUSION: Our study provides a new chart and reference values for normal uterine cervical length throughout gestation based on a large sample in the center of Iran. There was a progressive decrease in mean uterine cervical length with increasing gestational age in the population of this study. Our established charts for uterine cervical length throughout gestation might be more useful than a single cut-off value for more efficient prevention and management of preterm birth.