Sonographic assessment of the lower uterine segment during active labor in women with or without a uterine scar–a prospective study

Objectives: No study thus far has evaluated the LUS thickness in active labor. In this study, we endeavored to assess the LUS during active labor. Methods: Using transabdominal sonography in the mid-sagittal position with a full urinary bladder, the thickness of the LUS was measured during active labor phase in women with or without a history of a previous cesarean section. Results: A total of 28 women with a previous cesarean delivery were compared to 29 women without a history of uterine surgery. The median LUS was significantly thinner in women with a uterine scar both during (4 versus 5 mm, p =.001) and between contractions (5 versus 7 mm, p =.011). Paired comparison of LUS thickness between and during contractions within each group showed that thinning of LUS during contraction was significant for both the previous CS group (p <.001) and the control group (p <.001). We found no correlation between LUS thickness and chances of successful TOLAC. Conclusions: In this study, we characterized for the first time the LUS during active labor. We found that LUS was significantly thinner in women after a previous CS and that the LUS was significantly thinner during contraction.