Time-related changes of cervical length as a predictor of labor onset within one week using transvaginal ultrasonography.

OBJECTIVE

To assess the value of transvaginal cervical length (CL) measurement and funneling of the internal cervical os to predict the onset of spontaneous labor within one week.

DESIGN

Observational prospective study.

POPULATION: A total of 234 women who delivered after spontaneous onset of labor.

METHODS

CL was measured and the presence of funneling of the internal cervical os was recorded by transvaginal ultrasound examination.

MAIN OUTCOME MEASURES: CL changes from 37 to 40 weeks of gestation as a one-point measurement, as well as the long-term (16-21 weeks to term or 37-40 weeks) and short-term (weekly from 37 to 40 weeks) differences in CL.

RESULTS

The one-point measurement of CL, with an optimum cut-off point of 25 mm [odds ratio (OR) 3.19; 95% confidence interval (CI) 2.01-5.05] and a decreased long-term CL (cervical shortening of 55% as an optimum cut-off point (OR 3.75; 95% CI 1.76-8.00) may predict the onset of spontaneous labor within one week. The likelihood of spontaneous labor within one week is high when funneling of the internal cervical os is present (OR 2.68; 95% CI 1.71-4.19).

CONCLUSIONS

Transvaginal CL measurement and observation of funneling of the internal cervical os are useful predictors of the onset of spontaneous labor.