The Spiral Trial: A multicenter, randomized, controlled trial of Spiral thread sutures versus conventional thread sutures to prevent thinning of uterine scars following elective cesarean section

Background: The aim of this randomized controlled trial (RCT) is to investigate whether Spiral-thread sutures are superior to conventional sutures (0-Vicryl) for preventing uterine scar thinning following elective cesarean section. Methods: This multicenter, parallel-group RCT will be conducted in four hospitals across three medical regions in Japan to assess 200 women (≥20 years old) with singleton pregnancies who are scheduled to undergo cesarean sections. Eligible women will be randomly assigned (1:1 ratio) to receive either the conventional uterine suture continuous absorption thread, which is most commonly used in Japan, or the Spiral thread. The primary endpoint is the degree of scar thinning, measured by transvaginal ultrasonography 6–7 months postoperatively, to evaluate the position of the uterus (anterior or posterior tilt) and myometrial wound thickness. The degree of thinning will be compared between the groups, and four measurements (mm) of the thinning area, including caudal distance, depth of the depression, remaining thickness of the myometrium on the serous side of the most depressed area, and width of the depression, will be recorded in the sagittal view on transvaginal ultrasound. Secondary endpoints will include total operative time, suture application time (from birth to the end of uterine suturing), operative blood loss, number of additional Z-sutures or continuous sutures required to stop bleeding, maternal abnormality frequency (surgical complications and postoperative infections), surgeon's years of experience, and clinical interpretation of individual subscale scores. Discussion: This study shall provide important evidence on the optimal suture for preventing hysterotomy wound thinning after the first cesarean section. Trial registration: National Institute of Public Health, Japan: jRCT1062200001 (May 7, 2020; https://rctportal.niph.go.jp/en/detail?trial_id=jRCT1062200001) and Okayama University Certified Review Board: CRB6180001 (April 9, 2020, version 3.0).