Sonographic assessment of the cervix before, during, and after a uterine contraction is effective in predicting the course of labor

Using the traditional means of assessing the progress of labor, by vaginal examination at 2- to 3-hour intervals, an abnormal pattern of labor such as uterine dysfunction might not be detected before considerable time haspassed. The authors measured cervical length by transvaginal ultrasonography before, during, and after a contraction in the first stage of labor. The question was whether the degree of cervical change during contractions distinguishes between latent and active labor, and between a normal and abnormal labor pattern. The study group included 73 women at term after an uncomplicated pregnancy, 39 of whom were nulliparous. The entire cervix was imaged as uterine contractions were monitored by cardiotocography. Cervical length was measured as the distance between the internal os and external os along the inner surface of the posterior cervical lip. The degree of shortening was expressed as the decrease in cervical length at the peak of a contraction as a percentage of the precontraction length. Five labor patterns were distinguished: normal latent phase (n-latent), prolonged latent phase (p-latent), normal active phase (n-active), protracted active phase (p-active), and false labor. In women in the n-active and p-active groups, the cervix was more dilated and effaced than in the other 3 groups. On average, cervical length was diminished by approximately half during a contraction in normal labor. Assessing the station of the fetal head yielded similar findings, but p-latent women had a significantly higher station than the n-latent group. When cervical length was measured just before a contraction began, there were significant differences between the n-active and false labor groups, and between the p-active and the n-latent, p-latent, and false labor groups. Measurements made just after a contraction did not differ significantly from the precontraction length except in the n-active phase. Only in the n-latent and n-active groups did cervical length decrease to a significant degree. There were no significant differences in degree of cervical shortening between the parous and nulliparous women in the n-latent and n-active phases. Real-time ultrasound study of the cervix during uterine contractions could help to distinguish between normal and inefficient contractions, and in this way predict the subsequent course of labor.