Sonographic evaluation of cervical length in pregnancy: diagnosis and management of preterm cervical effacement in patients at risk for premature delivery.

Sonographic measurement of cervical length during pregnancy can provide an objective, noninvasive assessment of anatomical shortening associated with premature labor and delivery. One hundred fifty normal women underwent serial sonographic cervical length measurements during uncomplicated pregnancy. The mean cervical length was 52 +/- 12 mm until 34 weeks' gestation, when gradual effacement and cervical length shortening began. Using these data, we managed 88 pregnant women with previous second-trimester pregnancy losses by a combination of cerclage placement for cervical length less than 40 mm and aggressive therapy for premature uterine contractions. The results showed the following: 1) 97% of women with diethylstilbestrol exposure and 80% of women with müllerian abnormalities exhibited cervical length shortening; 2) only 60% of women with a normal uterine cavity showed cervical lengths of less than 40 mm; and 3) all three groups of high-risk patients, independent of cervical length, showed significant premature uterine activity. These observations suggest that sonographic cervical length measurement may be a useful adjunct in the assessment of anatomical cervical integrity and the decision for cerclage placement. Furthermore, the presence of both premature cervical length shortening and preterm uterine activity in 65% of high-risk patients suggests that "cervical incompetence" and premature labor may not be distinct entities, but common symptoms associated with an increased risk of preterm delivery.