Aim: To elucidate the clinical significance of progressive cervical length (CL) shortening before 31 weeks' gestation.
Methods: Transvaginal ultrasonography was used for longitudinal measurements of CL in 114 singletons. CL shortening groups were defined as having a CL of < 25 mm at < 26 weeks (early shortening group, 20 cases) and < 31 weeks (late shortening group, 19 cases). The control group (75 cases) was defined as having a CL of >= 25 mm at < 31 weeks. The CL values at 16-20, 21-25, 26-30 and 31-35 weeks, the age-related CL changes, the treatments for preterm labor, and the outcomes were compared between groups. In 78 cases with spontaneous delivery at >= 36 weeks, we investigated cervical dilatation velocity in the active phase of labor.
Results: At 16-20 weeks, CL values for the early group were smaller than those of the late and control groups. Rapid CL shortening occurred between 16-20 and 21-25 weeks in the early group and between 21-25 and 26-30 weeks in the late group. In the early group, all cases received cerclage and/or tocolysis or bedrest, and one case delivered prematurely. In the late group, 10 cases required tocolysis or bedrest, and one case delivered prematurely. In nulliparous women, cervical dilatation velocity in the early and late groups was more rapid than in the controls.
Conclusions: CL shortening to < 25 mm before 31 weeks is a risk factor for preterm delivery, as well as for preterm labor in cases who had tocolysis and bedrest, and precipitate delivery.