New ultrasonographic risk assessment of uterine scar dehiscence in pregnancy after cesarean section.

PURPOSE: We performed a new ultrasonographic risk assessment of uterine scar dehiscence, which is a potential risk factor for uterine rupture, in pregnancy after cesarean section. We attempted to shed light on the natural course of the change in the lower uterine segment by means of a longitudinal investigation through quantitative and qualitative evaluations.

METHODS

This retrospective single-center study involved 31 women with a normal singleton pregnancy delivered by elective cesarean section between 2020 and 2021, with all women showing a "niche" in the lower uterine segments. The lower uterine segments were assessed qualitatively and quantitatively using transvaginal ultrasonography at 16-21, 22-27, and 28-33 weeks of gestation, and subjects were divided into two groups: those with uterine dehiscence (12 women) and those without uterine dehiscence (19 women), depending on the gross findings of the lower uterine segments at cesarean section. Analyses were performed using Wilcoxon's rank-sum and Mann-Whitney U test with a significance level of P < 0.05.

RESULTS

The lower uterine segments changed from V-shaped to U-shaped to thin as gestation progressed and was more prominent in the uterine dehiscence group, occurring mostly at 22-27 weeks. At 22-27 weeks, the median myometrial thickness in the uterine dehiscence group was lower than in the group without uterine dehiscence (P = 0.0030). Thinning of the lower uterine segments had moved the cephalad at 22-27 and 28-33 weeks in cases with and without uterine dehiscence.

CONCLUSION

A model of morphological changes in the niche was constructed based on qualitative and quantitative assessments. The morphological changes and actual thinning of the lower uterine segments were prominent in the second trimester in women considered to have uterine scar dehiscence.