Objective: The objectives of the investigation were to study the association between levator hiatus dimensions in late pregnancy and both the length of second stage of labor and also the delivery mode in women delivering their first child.
Study design: In this cohort study, 231 nulliparous women were examined with 3- and 4-dimensional transperineal ultrasonography at 37 weeks of gestation. The anteroposterior, transverse diameter, and the area of levator hiatus were measured at rest, during levator ani muscle contraction, and during Valsalva maneuver. The second stage of labor was divided into passive and active second stage and delivery modes into normal vaginal or instrumental deliveries. Spearman correlation coefficient, independent-sample t test, and standard logistic regression were used for analysis.
Results: Larger levator hiatus dimensions at rest and during contraction at 37 weeks of gestation correlated with a shorter duration of the active second stage in women with normal vaginal delivery (Spearman correlation coefficient, -0.13 to -0.35, P ≤ .08). Women having normal vaginal deliveries had significantly larger transverse diameter at rest, during contraction, and during Valsalva maneuver compared with women having instrumental deliveries (mean difference, 0.29; 95% confidence interval (CI), 0.16-0.41; mean difference, 0.33; 95% CI, 0.21-0.44 and mean difference, 0.24; 95% CI, 0.06-0.42; P < .05). The same was true for the levator hiatus area at rest and during contraction (mean difference, 1.22; 95% CI, 0.37-2.07 and mean difference, 0.84; 95% CI, 0.22-1.46; P < .01). These estimates were unchanged by adjustments in the logistic regression analysis.
Conclusion: Larger levator hiatus dimensions in late pregnancy had a significant association with a shorter active second stage of labor and normal vaginal delivery.
Keywords: 3- and 4-dimensional transperineal ultrasound; delivery duration; delivery mode; levator ani muscle; levator hiatus dimension.
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