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To examine the association between third trimester cervical length (CL) measurement and duration of the first stage of labor.
This prospective cohort study included women with a singleton pregnancy who had routine CL measurements taken by transvaginal ultrasonography between 37 and 39 weeks gestation. Subjective duration of the first stage of labor was defined as the duration of contractions that the women subjectively had from the onset of regular contractions to full effacement of the cervix. Objective duration of first stage of labor was defined as 3 cm cervical dilation independent of cervical effacement until full effacement of the cervix. Associations between variables were analyzed using nonparametric correlations coefficients. A model relating the duration of labor to predictors was built using linear regression.
In this analysis a total of 129 women were included. There was no significant correlation between CL and subjective duration of labor (ρ = −0.037, p = 0.695); however, a reduction in CL increased the objective duration of the first stage of labor (ρ = −0.269, p = 0.013). In univariate analysis parity (p = 0.018), hypertensive disorders (p = 0.013) and induction of labor (p = 0.022) were significantly associated with subjective duration of the first stage of labor.
A long cervix in the third trimester is not associated with a prolonged first stage of labor. Induction of labor and multiparity were associated with a shorter first stage of labor while hypertension was associated with a longer duration of labor.