Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length.

Risk assessment for preterm delivery remains difficult, particularly among women with no prior history of preterm birth. We hypothesized that accurate assessment of cervical length by endovaginal ultrasonography could predict preterm delivery risk. A total of 178 patients with singleton gestations and without cervical incompetence were studied with transabdominal ultrasonography and endovaginal ultrasonographic cervical length measurement and manual vaginal examination of cervical length. A total of 113 patients who were evaluated by 30 weeks' gestation (excluding four induced preterm deliveries) were analyzed. Preterm delivery risk was compared between women with cervical lengths equal to or greater than the median and those with cervical lengths less than the median. An endovaginal ultrasonographic cervical measurement less than 39 mm was associated with a significantly increased risk of preterm delivery (25.0% versus 6.7%) and detected 76% of preterm births. Manual examination of cervical effacement detected 71% of preterm births, but transabdominal ultrasonographic measurement of cervical length was not preditive. Endovaginal ultrasonographic cervical measurement predicted increased preterm delivery risk regardless of parity or obstetric history. Endovaginal ultrasonography is a promising method for the prediction of risk of preterm birth. Because it has the potential to be an objective measure of cervical length, endovaginal ultrasonography may be superior to manual digital examination for preterm delivery risk assessment.