Objectives: To construct charts for cervical length in a low risk population measured by transvaginal ultrasonography.
Methods: Pregnant women of an apparently normal population were seen in the ultrasound division of the University Women's Hospital Basel between 20 and 34 weeks of gestation and underwent once (one measurement per subject) a transvaginal ultrasound measurement of the cervix under standardized conditions. In order to establish normal values of the cervical length, finally only women who delivered spontaneously at term (>37 weeks of gestation) remained in the study. Exclusion criteria were preterm labor, multiple pregnancies, cerclage or surgical intervention prior to pregnancy. For statistical evaluation, regression analysis and calculation of 5th and 95th percentiles were performed.
Results: A total of 669 cervical measurements were recorded. The number of measurements differed from 22 measurements at 23 weeks of gestation to 86 at 31 weeks of gestation. Cervical length gradually and significantly decreased as the gestational age progressed (between 20 and 34 weeks of gestation). New charts with the 5th, 50th and 95th percentile are presented and compared with previously published data.
Conclusions: Our charts for cervical length in a limited risk population can be used for observing patients at high risk of preterm delivery and for clearly identifying a significant deviation or decline in the percentile for these subjects.