[Risk predictors for preterm birth].

Among the clinical factors for preterm birth, some confer substantial increased risk, including a history of preterm birth, multiple gestation and vaginal bleeding in the second trimester. However, these factors are present only in a minority of women who ultimately deliver preterm and thus have low sensitivity. Cervical dilatation, effacement and position as determined by manual examination have been related to an increased risk of preterm birth but also suffer from low sensitivity and positive predictive values. Cervical length measured with transvaginal ultrasound has also been related to an increased risk of preterm birth as cervical length decreases. The reported sensitivity is better than other tests, but positive predictive value is low. The principal utility of the fetal fibronectin assay lies in its negative predictive value in symptomatic women. Increased sensitivity has been reported when cervical length is used in combination with fetal fibronectin.