Evaluation of the upper uterine cervix by the location of the vesicocervical fold of the urinary bladder to rule out cervical shortening during pregnancy with and without premature contractions

Objectives. To measure the length of the upper and lower cervix, as demarcated anatomically by the lowermost edge of the urinary bladder, in second- and third-trimester pregnancies with and without premature contractions. We hypothesized that patients with active premature contractions have a shorter upper cervix, placing them at greater risk of preterm delivery. Methods. The lengths of the total cervix and of the upper and lower cervix, separately, and funnelling of the internal os, were assessed by endovaginal ultrasonography. In 120 women with normal pregnancy (43 of which with premature contractions), cervical dilatation and effacement were determined by digital examination. The correlation of cervical variables with the course of pregnancy was analyzed by the Wilcoxon test. Results. The mean lengths of the upper and lower cervix were 15.9 ± 1.7 mm (median 16.0 mm) and 26.4 ± 3.7 mm (median 27.0 mm), respectively, in patients without premature contractions and 6.9 ± 3.7 mm (median 6.0 mm) and 24.7 ± 4.7 mm (median 25.0 mm), respectively, in patients with premature contractions. In the latter subgroup, the upper cervix was significantly shorter (p = 0.0001) but the lower cervix remained almost unchanged. Digital palpation was less accurate than transvaginal sonography for evaluating total cervical length. Conclusions. Transvaginal sonography is the method of choice for assessing cervical changes during pregnancy. In this prospective study, upper cervical length was the best predictor of preterm labor of all cervical parameters studied. Its length could be accurately determined by the location of the lowermost edge of the urinary bladder (vesicocervical fold of the bladder).