In China, the proportion of caesarean sections (CSs) performed in 2010 was 35–58%, which has attracted significant concern regarding the development of CSDs 12. With the increasing CS rate and the implemented two-child policy in China, the complications of CSDs, such as prolonged menstrual bleeding, secondary infertility, and even uterine rupture during a subsequent pregnancy, have emerged as important clinical problems13. Therefore, it is necessary to evaluate cesarean section scarring before the next pregnancy.
CSDs can be detected by transvaginal ultrasound (TVU) 3, 14, hysterography, sonohysterography (SHG), magnetic resonance imaging (MRI), and hysteroscopy (HSC) 15–18. Among these methods, transvaginal sonography is a simple, low-cost, and noninvasive examination that should be considered as the first choice for screening19; nevertheless, unskilled gynecologists or the use of a low-resolution ultrasound machine can miss defects during routine ultrasound scans, especially if the operator does not suspect a CSD and there does not look for a defect.
N. Singhl et al20 evaluated scar thickness in pregnant patients with previous caesarean section by TVS and magnetic resonance imaging (MRI) to determine the precision of radiologically measured scar thickness with the actual measured scar thickness. These measurements were correlated with each other and with the scar thickness measured during elective repeat caesarean section using a caliper. The study showed that the thickness measured with TVS had a better correlation coefficient with the actual scar thickness than the thickness measured with MRI (R = 0.72 vs. R = 0.59). Marasinghe’s research had similar conclusions21. These authors all relieved that TVS could be considered the preferred modality for antenatal scar thickness measurements.
Therefore, our study established a CSD risk assessment model by applying TVS to evaluate the uterine scar healing of 607 women with a history of cesarean section. The results showed that the TRM measured with TVS effectively predicted CSDs when TRM was less than 4.15 mm, and uterine incision diverticulum was more easily detected below this thickness threshold. In other words, if the detected TRM was less than 4.15 mm by ultrasonography, but a CSD was not found, it was suggested that the scar condition should be re-evaluated by other imaging examinations. This method could avoid missed diagnoses of poor uterine scar healing.
A study by Hayakawa et al., in turn, enrolled a total of 137 women and demonstrated that double-layer interrupted sutures reduced the prevalence of myometrial defects after CS 30–38 days after surgery22. Another randomized study that enrolled 78 women with scar thicknesses evaluated by TVS 40–42 days after surgery found that suturing all the myometrial layers, including the endometrium, reduced the risk for inadequate healing and incomplete regeneration23, 24. Finally, a retrospective study by Sevket at al., which applied the longest follow-up period of 6 months, showed that the use of a double layer locked/unlocked suture after CS promoted complete healing25. This finding is consistent with the follow-up results of our previous study about the transvaginal repair of CSDs, which showed that the wound healing was stable six months after surgery. In this study, women were followed up for more than 6 months after cesarean section.
The clinical guidelines for the treatment of CSDs remain unclear. Several successful surgical treatments for CSDs have been reported in recent years, including hysteroscopic resection, laparoscopic surgery, laparoscopic and hysteroscopic repair, and vaginal repair. In our previous studies, at 6 months after surgery, 80.3% of patients (94 of 117) reached ≤ 10 days of menstruation, 48 patients (63.2%) had no CSDs, and 11 patients (14.5%) had a > 70% reduction in CSD volume; additionally, CSDs still existed in approximately 40% of patients after vaginal repair 26. As long as the TRM increased and their menstrual symptoms improved, the repair surgery could still be considered effective in increasing the safety of the second pregnancy. However, no clinical guidelines have been issued for the management of CSDs with intermenstrual bleeding and/or thickness of the remaining muscular layer (TRM) or for the residual muscle thickness that is considered the ideal result of a repair. Therefore, we need to evaluate uterine scar healing in women after cesarean section to obtain the average level of scar recovery.