Transvaginal sonographic assessment of cervical dynamics during the third trimester of normal pregnancy

To obtain a normogram of measurements of the uterine cervix by transvaginal sonography during the third trimester of normal primiparous pregnancies and to relate these measurements to the events surrounding labor.

A prospective observational study, set in Guangzhou, Peoples Republic of China, was undertaken. Fifty-five normal nulliparous Chinese women with singleton pregnancies were studied from 30 weeks gestation until delivery. Serial transvaginal ultrasound examinations were performed at 30, 32, 34 and 36 weeks gestation and weekly thereafter.

There was a significant correlation between gestational age and cervical length and width. Funnelling of the internal os was present in 25% of cases, and its earliest appearance was at 36 weeks. There was no consistent relationship between funnel length and width and gestational age. The duration of the first stage of labor was inversely correlated with the last ultrasound measurement of cervical length, but there was no relationship with either cervical width nor the presence of funnelling. The cervical changes in this population differed from those found in Caucasians.

There is a direct relationship between both cervical width and length and gestational age and an inverse relationship with cervical length and the duration of labor. Funnelling of the internal os was not a predictor of the early onset of labor. The dimensions and features of the Asian cervix differ from those of the Europeans, and this should be considered when conducting further studies of a similar nature.