Transvaginal ultrasonography of the cervix can assist physicians in determining cervical length and funneling and also may help identify women at high risk of preterm delivery. De Carvalho and colleagues assessed the predictive performance of cervical changes and obstetric history for preterm delivery.

In this historical cohort study, the authors evaluated records of 2,391 pregnant women who delivered at a Brazilian teaching hospital. All patients were offered transvaginal ultrasonography between 21 and 24 weeks’ gestation. Complete demographic and obstetric data were gathered for each patient, and gestational age was confirmed by first-trimester scan.

Final analysis included 66 mothers who delivered at 34 weeks or earlier (preterm delivery) and 1,892 mothers who delivered after 34 weeks (term delivery). Women who delivered preterm had a mean second trimester cervical length of 23.8 mm compared with 35.6 mm in women who delivered after 34 weeks. Cervical length of less than 20 mm was associated with a greater than 25 percent risk of preterm delivery. Cervical length was significantly lower in women who had a history of premature delivery. Only 31 women had funneling at the second trimester examination, but these women had a significantly lower gestational age at delivery compared with those without funneling (33.5 and 38.8 weeks, respectively). A multivariate analysis showed that only cervical length, funneling, and a history of preterm delivery were significantly associated with delivery at 34 weeks or earlier (odds ratios were 1.12, 6.29, and 2.71, respectively).

The authors conclude that the risk of preterm delivery was 7 percent for women with a second trimester cervical length of 20 mm. The risk increased to 34 percent in patients who also had funneling, and the risk increased to 59 percent in women who also had a history of preterm delivery. Mothers with a cervical length of 20 mm and a history of prematurity had a risk of approximately 18 percent. The authors recommend that physicians consider second trimester cervical length when identifying mothers at risk for preterm delivery, especially in patients with a history of preterm birth.