The Recovery of Serum AMH Levels after Conservative Surgery for Ovarian Endometriomas May Be due to the Transient Compensatory Follicular Activation of the Contralateral Ovary

Surgical treatment of ovarian endometriomas can affect postoperative ovarian function, and it is assumed that the mechanical and thermal damage caused by surgical manipulations may result in diminished ovarian reserve of the affected ovary. The effect on postoperative ovarian function varies depending on the surgical technique and the power devices,[] but it may also be influenced by age, severity of endometriosis, cyst diameter, and unilateral or bilateral ovarian endometriomas.[] Anti-Müllerian hormone (AMH) is mainly produced by the granulosa cells of the growing follicles and correlates with the number of remaining primordial follicles. AMH is thought to be a local mediator of primordial follicle activation.[] Serum AMH levels can predict ovarian responsiveness in assisted reproductive therapy and are used as an objective indicator of ovarian reserve. By comparing AMH levels before and after surgery, it may be possible to estimate the degree of invasiveness of surgical procedures to the ovaries, and it is expected to be applied to the evaluation of fertility-sparing surgery. Serum AMH levels significantly decrease after surgery for ovarian endometriomas compared to preoperative values, suggesting that the harmful surgical procedures may impact on ovarian function.[,] It has also been noted that transiently decreased serum AMH levels may rise again during the postoperative course.[,,] However, the factors that influence the degree of postoperative changes in AMH levels and their long-term trends, as well as the mechanisms of pre and postoperative changes in AMH levels, are not fully understood. In the present study, we retrospectively examined the longitudinal changes in serum AMH levels within 12 months in women who underwent laparoscopic surgery for ovarian endometriomas and clarified the mechanism that influence post operative serum AMH values by comparing these changes according to the different preoperative AMH levels and laterality (unilateral or bilateral) of the lesions.

Women at reproductive age who underwent laparoscopic surgery for ovarian endometriomas between April 2012 and March 2021, and whose serum AMH level was measured within 6 months before surgery, were selected. Only the subjects measured before the start of preoperative hormone therapy were included. In these subjects, serum AMH levels were measured every 3 months after the surgery at least once (range: 1–4) within 12 months after surgery. These women with unilateral or bilateral ovarian endometriomas received fertility-sparing surgery, such as cystectomy, cautery, cyst content drainage, or ethanol fixation, on at least one side of the ovary. Women who received a unilateral adnexectomy were excluded. Different types of surgical techniques were individually selected based on age, previous clinical course, cyst diameter, and localization of the cyst. The surgery was performed by a single surgeon (Kitajima M) with a well-trained assistant surgeon (Kajimura I and Matsumoto K) based on fixed surgical principles in a two-dimensional (2D) laparoscopy system. Patients were divided into two groups according to the preoperative AMH levels. Patients with AMH levels in the range of 1.2–6.0 ng/mL were designated as “normal ovarian reserve, NOR group,” and patients with AMH levels below 1.2 ng/mL were designated as “diminished ovarian reserve, DOR group.” Women with preoperative AMH levels higher than 6.0 ng/mL were excluded from this study. Regarding the clinical backgrounds, age at the surgery, maximum diameter of cysts, preoperative blood AMH level, and total rASRM score[] were compared between the groups, and they were also differentially compared according to the women with unilateral and bilateral lesions. In women with bilateral lesions, cyst diameter was calculated as the sum of the maximum diameters of each cyst. Postoperative changes in serum AMH levels were calculated as the difference from the preoperative value (preoperative AMH value – postoperative AMH value: unit ng/mL) and plotted according to the time points after surgery (1, 3, 6, 9, and 12 months). Serum AMH levels were measured by the electrochemiluminescence immunoassay, the roche elecsys amh assay, srl laboratory, tokyo, japan (ECLIA) (the Roche Elecsys AMH assay, SRL laboratory, Tokyo, Japan). Preoperative AMH values were measured at the early follicular phase, and postoperative AMH values were measured regardless of menstrual cycle, and some women were under the postoperative medical therapy (low-dose oral estrogen/progestin contraceptives or oral progestin). Statistical analysis was performed by Student’s t-test for comparing continuous variables and by Chi-square test with Bonferroni correction for comparing binomial variables using computer software, and graph charts were created by the same software (JMP ver. 16, SAS Institute Japan, Tokyo, Japan), and P < 0.05 was considered a significant difference. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Clinical Research Ethics Committee of Nagasaki University Hospital (Approval No. 24041101). The patient consent was waived by IRB.

Fifty-six women were included in the study. Of the 40 women in the NOR group, 24 were unilateral, and 16 were bilateral, and of the 16 women in the DOR group, 8 were unilateral, and 8 were bilateral. The age was significantly higher in the DOR group (36.8 ± 2.7 vs. 30.8 ± 4.6 years, P < 0.05), but there was no significant difference in the cyst diameter between the two groups. The rASRM score was significantly higher in the DOR group. Further comparison within the NOR and DOR groups according to the unilateral and bilateral cases was performed. In the NOR group, the age was significantly lower in women with unilateral lesions than in those with bilateral lesions (29.5 ± 4.2 vs. 32.7 ± 4.5 years, P < 0.05). The total rASRM classification score was significantly higher in women with bilateral lesions than in those with unilateral lesions (76 ± 43 vs. 42 ± 15, P < 0.05). There was no significant difference in cyst diameter and preoperative blood AMH levels according to the laterality in the NOR group. In the DOR group, there were no significant differences in age, cyst diameter, preoperative AMH level, or total rASRM score between women with unilateral lesions and those with bilateral lesions [Table 1]. In terms of surgical technique, cystectomy accounted for the majority of unilateral cases (26 cases, 62.5%), followed by cyst ablation only (4 cases), and drainage alone and ethanol sclerotherapy (1 case each). In the bilateral cases, unilateral cyst removal and contralateral cautery accounted for the largest number of cases (10 cases, 41.7%), followed by bilateral cyst ablation in 8 cases, bilateral cyst removal in 3 cases, unilateral cautery alone in 2 cases, and unilateral cyst removal alone in 1 case. The average number of serum AMH measurements during 12 months after surgery was 3.3 (range 1–5). A comparison of the difference in AMH levels before and after surgery between NOR and DOR groups showed that the NOR group showed an apparent transient decline in serum AMH levels 1–3 months after surgery but recovered 6–9 months after surgery. On the other hand, the DOR group also showed a tendency to decline immediately after surgery and showed slow recovery, although the amplitude of the change was small. Furthermore, when the AMH levels of the NOR and DOR groups were classified into unilateral and bilateral subjects, after the immediate decline, serum AMH levels showed a recovery to a similar level as the preoperative level at 6–9 months postoperatively, only in the unilateral case of the NOR group. In the bilateral group, the amplitude of decline was greater than that of the unilateral group, and there was no trend toward recovery. In the DOR group, there was no clear difference in the transient change between the unilateral and bilateral cases [Table 2 and Figure 1]. We noticed that there were cases in which the serum AMH level increased postoperatively from the preoperative value, and when a difference of 1.0 ng/mL more or less from the preoperative value (considering the intra-assay coefficient of variability of this test is within ±20% according to the manufacturer’s instruction) was considered a meaningful increase, the increase was observed in only unilateral cases of the NOR group [Figure 1]. These five patients were relatively young, ranging in age from 23 to 33 years, and all had cysts larger than 5 cm in diameter, including one case with a diameter of more than 10 cm. In these cases, unilateral cystectomy was performed, and no additional surgical manipulation was performed in the unaffected contralateral ovary. Preoperative AMH levels averaged 3.86 ng/mL (range 2.90–4.47 ng/mL) and reached a maximum at 6–12 months postoperatively, with a range of 1.12–6.79 ng/mL between preoperative and maximum values [Table 3].

In this study, we found that serum AMH levels transiently fluctuate after surgery. In women with normal ovarian reserve, the immediate decline is unavoidable, but the recovery can be seen in women with unilateral cysts at around 9–12 months after surgery. The amplitude of decline may be doubled in women with bilateral cysts, and the recovery cannot be expected in most cases. Surprisingly, some women with unilateral cysts showed apparently higher AMH levels after surgery compared to baseline AMH levels before surgery. Women with diminished ovarian reserve (DOR) also showed postsurgical fluctuations in serum AMH levels, but the amplitude of the change may be clinically insignificant. We did not find the difference in postoperative serum AMH levels between unilateral and bilateral in woman with DOR. AMH is produced exclusively by the granulosa cells of growing follicles. It has been used as a marker of ovarian reserve and a predictor of ovarian response in ART. Serum AMH levels decline with age in women of reproductive age and can be assessed objectively, independent of the menstrual cycle. However, serum AMH values may vary widely among women of the same age. In addition, no specific threshold has been established to predict future fecundability, and its predictive ability appears to be limited.[] Several factors – including surgery, medications, body mass index, and smoking – may influence serum AMH levels. Although surgery may reduce serum AMH values, the association between the invasiveness of surgery and the extent of decline remains controversial. In some previous reports, serum AMH levels after cystectomy are often lower than preoperative levels up to 6 months postoperatively but tend to recover by 12 months postoperatively.[,,] The degree of decline differs depending on the location of ovarian endometriomas (bilateral or unilateral), and bilateral cystectomy resulted in lower postoperative serum AMH levels than those of unilateral cystectomy.[,,,,] In addition, time trends show that AMH levels tend to recover by 12 months postoperatively in unilateral cysts, while AMH levels tend to be less likely to recover in bilateral cysts.[] Lind et al. studied surgical decline in serum AMH levels in benign ovarian cysts, including ovarian endometriomas, and found no change in AMH values 6 months postoperatively in women with preoperative AMH levels <1.1 ng/mL,[] similar to our present results. If the ovarian reserve is markedly low preoperatively, the number of follicles has already diminished, and the AMH value may not significantly fluctuate due to surgical invasion or differences in cyst localization. On the other hand, it has been reported that women with low preoperative AMH levels are more likely to have decreased AMH levels postoperatively and that these declines tend to persist for long term.[,] Ozaki et al. reported that women with low preoperative AMH values and had bilateral cystectomy are at high risk of postsurgical DOR.[] It is essential that the gynecological surgeon should pay careful attention to protect residual ovarian reserve in women with low preoperative AMH levels, but should not avoid recommending adequate opportunity for surgical interventions in symptomatic infertile women. Lee et al. reported that the three-dimensional endoscope improves speed and reduces the number of performance errors and has a greater probability of visualizing a positive lesion when compared to the 2D laparoscope.[] When applying surgery to such women with endometriomas, the surgical technique and instruments that lower the impact of surgical invasiveness may improve the postoperative ovarian functions. In this study, we found that certain women showed marked elevation in postoperative serum AMH levels. Lind et al. also reported a case of postoperative AMH elevation, but their clinical background was not unique.[] In the present study, young, unilateral with relatively higher ovarian reserve, with a mean preoperative serum AMH level of 3.86 ng/mL, and with the intact contralateral ovary without any superficial endometriotic lesions showed elevation. In addition, the cyst diameters of five women were >5 cm, with an average of 7.8 cm and a maximum of 11 cm. Previous reports have indicated a tendency for higher preoperative serum AMH levels when the cyst diameter of the ovarian endometrioma is large,[,] and Roman et al. reported that preoperative serum AMH levels are high in women with large ovarian endometriomas but that the larger the cyst diameter, the greater the invasion of normal ovarian tissue by cyst excision.[] We propose the following hypothesis in the cases of postoperative AMH elevation observed in the present study: Surgical treatment of a relatively large ovarian endometrioma may damage residual normal ovarian cortex and result in a sudden decrease in local AMH level. Since AMH plays a local inhibitory role in follicular recruitment, a sudden decrease in AMH levels may result in enhanced recruitment of dormant follicles when ovarian reserve is maintained in the contralateral normal ovary, and in some cases, serum AMH levels may show marked elevation above preoperative levels. These are thought to be a functional compensation. Interestingly, compensatory changes in the remaining normal ovary have been noted after unilateral adnexectomy, including women with endometriosis.[,] It may be hypothesized that surgical invasion for ovarian endometrioma may damage ovarian function on the affected side, while compensatory enhanced recruitment of follicles in the contralateral ovary may occur in women with normal ovarian reserve [Figure 2]. From our present study, surgical invasion of ovarian endometriomas may affect equally unilateral and bilateral lesions, as reflected by an immediate decrease in postoperative serum AMH levels, which were greater in the bilateral cases. Even when preoperative AMH levels were normal and ovarian reserve was preserved, bilateral cases showed poor recovery of serum AMH levels at 6–9 months postoperatively, suggesting that the changes in serum AMH levels observed in many cases at 6–9 months postoperatively may have been due to compensatory changes in the contralateral normal ovary. On the other hand, in the unilateral cases with DOR, the changes in ovarian reserve due to surgical invasion could not be compensated for, and the degree of recovery might have been smaller. Yu et al. reported that postoperative ART results were not significantly different between women who had surgery for unilateral endometrioma and those with bilateral endometriomas. However, in this report, the number of retrieved oocytes was significantly lower in women who had surgery for bilateral lesions.[] Serum AMH level may be an indicator of ovarian reserve, but it is difficult to estimate the exact ovarian reserve of each ovary. In women with unilateral cases whose AMH levels recovered after surgery, it is possible that the ovarian function of the affected ovary was maintained by a minimally invasive surgical technique, but it is also possible that maintained AMH levels merely reflect that the opposite side ovary compensated for the invasion on the affected side. This should be kept in mind when evaluating the effect of a surgical procedure on ovarian function based on serum AMH levels alone. This study may possess several limitations that should be considered for the interpretation of the results. This is a retrospective study with a limited number of cases, and the surgical technique differed in some women. Prospective follow-up with unified surgical methods may bring about more solid conclusions. In addition, threshold values for serum AMH levels define diminished ovarian reserve or postoperative decline, or elevation from preoperative values have not been well confirmed. The clinical significance of the degree of decline in postoperative AMH levels may depend on preoperative values. Even though there were large decline after surgery, women with high preoperative AMH levels may not show the disadvantage of the surgical damage. On the contrary, a small decline after surgery may be more important in women designated as DOR preoperatively. To evaluate postoperative ovarian function, this study examined the postoperative changes in serum AMH levels alone. Other measures exist for evaluating ovarian function, and AMH alone may not be sufficient to assess postoperative ovarian function or fertility. Thus, the compensatory mechanism after the surgery for unilateral endometrioma should be confirmed by some other clinical measures of ovarian function, such as responsiveness to ovarian stimulation, postoperative AFC, and the result of infertility treatment. In our study, only 13 out of 56 women (4 unilateral and 9 bilateral) underwent IVF after fertility-sparing surgery. Due to the small number of cases, it was difficult to assess the impact of the recovery of AMH on these cases.

Differences in preoperative AMH levels and the unilateral or bilateral nature of cysts are important factors for predicting postoperative AMH levels and therefore in the selection of surgical interventions and other treatment strategies. On the other hand, postoperative recovery of serum AMH level may reflect compensative production from the contralateral ovary; however, the mechanisms that affect AMH levels after the surgery for endometriomas should be validated in future studies. Author contributions Conceptualization, Michio Kitajima; Methodology, Michio Kitajima; Software, Itsuki Kajimura and Michio Kitajima; Validation, Itsuki Kajimura, Chiaki Eishi, Asako Matsumura, Kanako Matsumoto, Ayumi Harada, Yuriko Kitajima and Michio Kitajima; Formal Analysis, Itsuki Kajimura and Michio Kitajima; Investigation, Itsuki Kajimura Chiaki Eishi, Asako Matsumura, Kanako Matsumoto, Ayumi Harada, Yuriko Kitajima and Michio Kitajima; Resources, Itsuki Kajimura and Michio Kitajima; Data Curation, Itsuki Kajimura and Michio Kitajima, Kiyonori Miura; Writing – Original Draft Preparation, Itsuki Kajimura, Michio Kitajima and Kiyonori Miura; Writing – Review and Editing, Itsuki Kajimura, Michio Kitajima, Kiyonori Miura; Visualization, Itsuki Kajimura and Michio Kitajima; Supervision, Michio Kitajima and Kiyonori Miura; Project Administration, Itsuki Kajimura and Michio Kitajima; Funding Acquisition, Itsuki Kajimura and Michio Kitajima. All authors have read and agreed to the final version of the manuscript. Data availability statement The datasets generated during and/or analyzed during the current study are not publicly available, but are available from the corresponding author on reasonable request. Financial support and sponsorship This study was supported in part by the Grants-in-Aid for Scientific Research (grant no. 21K09521) from the Japan Society for the Promotion of Sciences (to M.K.). Conflicts of interest There are no conflicts of interest.

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