OBJECTIVE: To establish a nomogram for the length of the uterocervical canal and to determine whether this can be used to predict preterm delivery. METHODS: Cervical length was measured by transvaginal ultrasonography in 32 women (21 primigravid, 11 multigravid) with threatened preterm delivery, and in 177 normal singleton pregnancies between 18-37 weeks' gestation. Regression analysis was used to create the nomogram. Student t test was used to compare the groups. RESULTS: A linear relationship was found between cervical length and gestational age (r = -0.4, P < .001). Comparison of cervical length on admission in the patients with threatened preterm delivery showed that 11 preterm deliveries occurred in women who had a mean cervical length of 23.2 mm (range 17-29), whereas 21 term deliveries occurred in women with a mean cervical length of 31.7 mm (range 21-42). The difference was significant (P