Transvaginal Sonographic Evaluation of Cesarean Section Scar Niche in Pregnancy: A Prospective Longitudinal Study

Abstract

Background and Objectives: To investigate the prevalence of a Cesarean section (CS) scar niche during pregnancy, assessed by transvaginal ultrasound imaging, and to relate scar measurements, demographic and obstetric variables to the niche evolution and final pregnancy outcome. Materials and Methods: In this prospective observational study, we used transvaginal sonography to examine the uterine scars of 122 women at 11+0–13+6, 18+0–20+6 and 32+0–35+6 weeks of gestation. A scar was defined as visible on pregnant status when the area of hypoechogenic myometrial discontinuity of the lower uterine segment was identified. The CS scar niche (“defect”) was defined as an indentation at the site of the CS scar with a depth of at least 2 mm in the sagittal plane. We measured the hypoechogenic part of the CS niche in two dimensions, as myometrial thickness adjacent to the niche and the residual myometrial thickness (RMT). In the second and third trimesters of pregnancy, the full lower uterine segment (LUS) thickness and the myometrial layer thickness were measured at the thinnest part of the scar area. Two independent examiners measured CS scars in a non-selected subset of patients (n = 24). Descriptive analysis was used to assess scar visibility, and the intraclass correlation coefficient (ICC) was calculated to show the strength of absolute agreement between two examiners for scar measurements. Factors associated with the CS scar niche, including maternal age, BMI, smoking status, previous vaginal delivery, obstetrics complications and a history of previous uterine curettage, were investigated. Clinical information about pregnancy outcomes and complications was obtained from the hospital’s electronic medical database. Results: The scar was visible in 77.9% of the women. Among those with a visible CS scar, the incidence of a CS scar niche was 51.6%. The intra- and interobserver agreement for CS scar niche measurements was excellent (ICC 0.98 and 0.89, respectively). Comparing subgroups of women in terms of CS scar niche (n = 49) and non-niche (n = 73), there was no statistically significant correlation between maternal age (p = 0.486), BMI (p = 0.529), gestational diabetes (p = 1.000), smoking status (p = 0.662), previous vaginal delivery after CS (p = 1.000) and niche development. Uterine scar niches were seen in 56.3% (18/48) of the women who had undergone uterine curettage, compared with 34.4% (31/74) without uterine curettage (p = 0.045). We observed an absence of correlation between the uterine scar niche at the first trimester of pregnancy and mode of delivery (p = 0.337). Two cases (4.7%) of uterine scar dehiscence were confirmed following a trial of vaginal delivery. Conclusions: Based on ultrasonography examination, the CS scar niche remained visible in half of the cases with a visible CS scar at the first trimester of pregnancy and could be reproducibly measured by a transvaginal scan. Previous uterine curettage was associated with an increased risk for uterine niche formation in a subsequent pregnancy. Uterine scar dehiscence might be potentially related to the CS scar niche.

Reproducibility of assessment of full‐dilatation Cesarean section scar in women undergoing second‐trimester screening for preterm birth

“…For second-trimester assessment of niche length, depth, width and RMT, the interobserver 95% LOA were all ≤ 4.0 mm, which is comparable to our interobserver reproducibility for offline 2D still images. Similar to our study, both Naji et al and, more recently, Savukyne et al reported CS scar detection rates of 88.8% and 77.9%, respectively, during pregnancy, with excellent agreement for CS scar and niche visibility 13,14 . Zimmer et al demonstrated that the ability to visualize the CS scar was significantly greater with increasing cervical dilatation at the time of CS 24 .…”

“…and, more recently, Savukyne et al . reported CS scar detection rates of 88.8% and 77.9%, respectively, during pregnancy, with excellent agreement for CS scar and niche visibility 13,14 . Zimmer et al .…”

“…It is hypothesized that a low uterine incision or cervical incision and intraoperative complications, such as tears and extensions of the initial CS incision, may lead to structural damage of the cervix and compromise its function in a subsequent pregnancy 10,12 . Two studies have assessed the visibility and reproducibility of sonographic assessment of the CS scar in pregnancy 13,14 . Naji et al reported that the CS scar was visible in 88.8% of women in the second trimester of pregnancy (19-21 weeks' gestation), with 100% interobserver agreement 13 .…”

Cesarean Scar Thickness Decreases during Pregnancy: A Prospective Longitudinal Study

“…Still, there is no known potential role of the ultrasound assessment of myometrial thickness in managing patients after cesarean delivery. We have previously shown a good inter- and intra-observer agreement for measurements of CS scar niche, RMT, and LUS thickness in all three trimesters of pregnancy [ 16 ]. More extensive and good quality studies are indicated to examine the uterine scar myometrial thickness ratio between trimesters or cut-off values for use in clinical practice, and to incorporate these measurements in deciding the mode of delivery or predict complications.…”

Prediction of Scar Myometrium Thickness and Previous Cesarean Scar Defect Using the Three‐Dimensional Vaginal Ultrasound

“…At present, the examination of uterine diverticulum mainly includes ordinary transabdominal and transvaginal two-dimensional color Doppler ultrasound, three-dimensional transvaginal ultrasound (TVUS), hysterography (SHG), magnetic resonance imaging (MRI), and hysteroscopy [ 17 ]. Uterine contrast-enhanced ultrasonography can well observe the existence of scarred diverticulum, but it cannot measure the size of the diverticulum, and some people are allergic to contrast agents.…”