Unveiling the Uterine Niche: The Impact of Isthmocele on Subsequent Pregnancy Outcomes

Abstract Caesarean section is the most commonly performed surgical procedure in women worldwide. One of its long-term complications is isthmocele, a defect in the caesarean section scar, also known as a niche or diverticulum. Despite the lack of clear diagnostic criteria, isthmocele is most often defined as a ≥2 mm depression in the uterine muscle at the site of the caesarean section scar, assessed by transvaginal ultrasound or other imaging techniques. The prevalence of the niche is difficult to estimate and depends on the population, time of assessment and diagnostic method. The aetiology of isthmocele is multifactorial, including abnormal suturing technique, low uterine incision, uterine retroversion, and wound healing disorders. In most women, the changes are asymptomatic, but some report intermenstrual bleeding, pelvic pain, or infertility. The niche may also increase the risk of complications in subsequent pregnancies, such as placenta praevia, placenta accreta spectrum, uterine rupture, or cesarean scar pregnancy. There are no clear guidelines for delivery after caesarean section with isthmocele; decisions are made on an individual basis, based on the thickness of the residual muscle. Surgical treatment-laparoscopic or hysteroscopic-can improve anatomical parameters and clinical symptoms, and modifying the technique of suturing the uterus during caesarean section can reduce the risk of niche formation.