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Am J Obstet Gynecol. 1999 Dec;181(6):1465-72.

Cervical length and dilatation of the internal cervical os detected by vaginal ultrasonography as markers for preterm delivery: A systematic review.

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Department of Obstetrics and Gynecology, University of Vienna, Austria.



We performed a systematic review to evaluate endovaginal cervical ultrasonography as a predictor of preterm delivery.


Selection criteria were original published English-language reports of prospective studies including women at <37 weeks' gestation with intact amniotic membranes. Parameters and outcomes were cervical length or dilatation of the internal cervical os and preterm delivery.


In 3 subgroups of studies including patients with preterm labor or low-risk, symptom-free patients with early (20-24 weeks) or late (27-32 weeks) ultrasonographic examination, optimal cutoff values for cervical lengths ranged between 18 and 30, 25 and 35, or 25 and 39 mm. At these cutoff values, sensitivity rates were between 68% and 100%, 33% and 54%, or 63% and 76%, and specificity rates were between 44% and 79%, 73% and 91%, or 59% and 69%, respectively. Sensitivity rates for dilatation of the internal cervical os were 70% to 100%, 16% to 25%, or 33%, and specificity rates were 54% to 75%, 95% to 99%, or 92%, respectively.


In patients with symptoms of preterm labor, endovaginal cervical ultrasonography appears to be an effective predictor of preterm delivery.

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