Intrapartum transperineal ultrasound for evaluating uterine contraction intensity in the second stage of labor

Purpose: To clarify whether intrapartum transperineal ultrasound (ITU) can be used to evaluate uterine contraction intensity, and whether the intensity is associated with the duration of the second stage. Methods: A prospective observational study was performed involving 86 women with a normal singleton term fetus and more than three contractions every 10 min. ITU was performed for contractile and non-contractile periods of labor at the beginning of the second stage, and one representative “angle of progression (AoP)” image was selected for each period. The Mann–Whitney U test was used to compare ∆AoP, the difference between the two angles, depending on the duration of the second stage. Receiver operating characteristic curves were used to evaluate the probability of duration of the second stage ≤50 min in nulliparous women. Results: Among nulliparous women, ΔAoP differed significantly according to the duration of the second stage (52.5° ± 5.0° for ≤50 min vs. 30.9° ± 2.1° for >50 min; P < 0.001). Receiver operating characteristic curve analysis showed that approximately 85% of nulliparous women with ΔAoP greater than 40° delivered within 50 min. Conclusion: These findings could be utilized in the evaluation of uterine contraction intensity, and ∆AoP measurement could be used to predict the duration of the second stage of labor in nulliparous women.