Evaluation of threatened preterm delivery by transvaginal ultrasonographic measurement of cervical length

To establish a nomogram for the length of the uterocervical canal and to determine whether this can be used to predict preterm delivery.

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.

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 < .001). A cervical length of less than 20 mm on admission had a positive predictive value of 100%. These patients had preterm delivery despite tocolytic therapy during hospitalization.

The risk of preterm delivery is high in women whose cervical length on admission is less than 30 mm, and strict management is required for those with a cervical length of less than 20 mm.