This study is the first to reveal that endometrial defects are frequently detected by hysteroscopy after adenomyomectomy and that postoperative endometrial evaluation may be beneficial in identifying patients at high risk for PAS and uterine rupture complications, enabling optimal management by waiting for endometrial restoration.

Of the pregnancies after adenomyomectomy reported herein, one presented with uterine rupture from the site of placenta percreta, a life-threatening condition for the mother and infant. Two cases of sudden-onset uterine rupture at 27 and 29 weeks of gestation related to placenta percreta have been reported, similar to our experience with case 1 [2, 3]. Uterine rupture is one of the most severe obstetric disorders, often associated with a history of uterine surgery. The frequency is 0.27–0.7% in vaginal deliveries after a previous cesarean section [11], 0.26% in pregnancies after myomectomy [12], and 3.2–12.5% in pregnancies after adenomyomectomy [1], suggesting a particularly high risk of uterine rupture after adenomyomectomy. Since uterine rupture after adenomyomectomy often occurs in PAS, predicting and preventing PAS, especially uterine rupture due to placenta percreta, is of utmost clinical importance.

Hysteroscopic evaluation following adenomyomectomy permitted the assessment of endometrial defects, which may be crucial in predicting uterine rupture in subsequent pregnancies. The extensive endometrial defect led to uterine rupture through the placenta percreta site in case 1. In case 4, where pregnancy was achieved after the extensive endometrial defect recovered to a minimal scar, placenta accreta requiring hysterectomy occurred, indicating that waiting for endometrial restoration could have prevented the severe complications seen in case 1. Of the 11 cases in this study, these two cases (18.2%) were diagnosed as PAS based on clinical intraoperative findings, and both required hysterectomy. The frequencies of clinically diagnosed PAS were 100%, 20%, and 0% for cases with preconceptional endometrial defects, endometrial restoration, and cases without endometrial defects, respectively. Therefore, patients with a history of postoperative endometrial defects are at high risk of PAS, even after endometrial recovery. In cases such as 5 and 6, where pregnancy was avoided while waiting for endometrial restoration, no PAS occurred. Since pathological analysis was performed in all pregnancies, pathological PAS was detected in 100%, 60%, and 20% of pregnancies with preconceptional endometrial defects, cases with endometrial restoration, and cases without endometrial defects, respectively, even if they were not clinically significant. This suggests that a history of endometrial defects might be associated with an increased number of potentially microscopically detected PAS lesions in the background of clinical PAS. Overall, waiting for endometrial healing may reduce the severity of PAS and uterine rupture complications.

PAS involves contact with the myometrium without a decidual membrane. Since the decidual membrane is derived from the maternal endometrium, it is reasonable to assume that placentation will not be successfully accomplished if endometrial defects are recognized prior to conception. There are reports that a history of operative hysteroscopy, adhesiolysis for Asherman’s syndrome, or cesarean section is associated with a high risk of PAS [8, 9]. Additionally, a study on pregnancy after myomectomy, which occurs more frequently after adenomyomectomy, revealed that patients with intraoperative endometrial breaches were significantly more likely to develop PAS than those without [13]. Endometrial injury leads to fibrosis, is reportedly associated with inadequate uterine blood flow, and impedes endometrial healing [14]. In addition to the incision of the endometrium, adenomyomectomy causes temporary insufficiency of blood flow in the surrounding myometrium [10], potentially prolonging healing. This study highlights that insufficient endometrial blood flow may contribute to PAS in subsequent pregnancies. Therefore, it is crucial to develop surgical techniques that prevent postoperative endometrial blood flow insufficiency. We believe that both residual adenomyosis near the endometrium and surgical damage to it can reduce endometrial blood flow in patients who have undergone adenomyomectomy. Our approach focuses on minimizing damage to the endometrial layer while removing as much of the adenomyotic lesion as possible. Preserving endometrial blood flow is likely achieved by minimizing endometrial damage, and maximal removal of adenomyosis makes it easier to reconstruct the uterus by suturing and forming the uterus. We believe that these approaches may support the restoration of uterine blood flow in subsequent pregnancies, but future studies are necessary to determine the relationship between endometrial damage, the extent of resection, and postoperative endometrial blood flow and fertility.

If endometrial defects were observed, hysteroscopy was repeated within 3–6 months. For patients who underwent adenomyomectomy, aggressive hormone replacement for endometrial restoration is challenging due to the risk of adenomyosis recurrence. Hence, allowing pregnancy after endometrial restoration while managing recurrence by taking dienogest may be advisable. In both patients for whom hysterectomy was required due to clinically diagnosed PAS in this report, endometritis was diagnosed before pregnancy, and pregnancy ensued after administering doxycycline hydrochloride hydrate, suggesting the possibility that pregnancy was achieved due to an improved endometrial condition outside the defect. Despite the small number of cases for conclusive findings, qualitative endometrial evaluation, including a history of endometritis treatment alongside hysteroscopic findings, might aid in predicting PAS development.

For predicting pregnancy complications after adenomyomectomy, Otsubo et al. reported that a uterine wall thickness of 7 mm or less on an MRI before pregnancy indicates a high risk for uterine rupture [4]. While they included two patients with uterine rupture related to placenta percreta at 16 and 19 weeks of gestation, uterine rupture after adenomyomectomy was most common at 30–32 weeks of gestation [15]. To date, no report exists on predicting uterine rupture after the second trimester of pregnancy. In our experience, the myometrium was less than 7 mm only in case 1, which presented with uterine rupture, suggesting that myometrial thinning might be beneficial in predicting uterine rupture in the midterm and beyond. Hysteroscopy offers a more detailed view of the endometrium, which is the basis for placentation, and may improve predicting PAS and uterine rupture complications. The weight of the resected adenomyosis, ART, and interval from adenomyomectomy to pregnancy revealed no clear correlation with PAS. Of the 11 pregnancies, nine were IVF-ET pregnancies, and for patients requiring adenomyectomy, embryo cryopreservation before surgery is often planned. In such patients, hysteroscopy can track endometrial changes over time and may be essential in determining the appropriate timing for embryo transfer.

The limitations of this study included the limited number of samples and its retrospective design. Since hysteroscopy was not conducted in patients where adenomyomectomy was performed at other hospitals, these patients were not included despite being perinatally managed at our institution. The duration needed for endometrial restoration and optimal treatment during this period require further study through the accumulation of more cases. Additionally, many patients attempting conception postadenomyomectomy are of advanced maternal age, necessitating individual determination of the waiting period for endometrial restoration through shared decision-making in prenatal counseling. Extending the period of contraception post-surgery can lead to significant psychological stress. Providing preconception counseling about the importance of waiting for endometrial restoration while considering the risk of PAS prior to adenomyomectomy helps patients better understand the treatment plan, alleviating anxiety and promoting mental resilience throughout the process.

Adenomyectomy is an essential treatment option for patients who wish to preserve their fertility. Patients should be thoroughly counseled about perinatal risks preoperatively, and postoperative endometrial evaluation via hysteroscopy may aid in determining the optimal timing for conception to mitigate the risk of PAS and uterine rupture complications.