Effects of intravenous tranexamic acid on ovarian reserve and intra-operative blood loss during laparoscopic cystectomy of endometriotic cyst: a pilot randomized controlled trial

Background: Strategies to preserve ovarian function after ovarian endometriotic cyst removal have been reported in many studies; however, no study has evaluated tranexamic acid administration during surgery.

To evaluate feasibility of conducting a definitive trial and assessing the potential efficacy of tranexamic acid on ovarian reserve and intra-operative blood loss by comparing mean differences in anti-Müllerian hormone (AMH) levels following laparoscopic ovarian cystectomy between tranexamic acid and control groups.

A parallel two-arm pilot trial was conducted with 40 participants with endometriotic cysts who underwent laparoscopic ovarian cystectomy. They were randomized 1:1 to either 1 g tranexamic acid (TXA) or no TXA ( n = 20 per group). TXA was administered to the participants immediately after induction of general anesthesia and intubation. The primary outcome was the feasibility of conducting a definitive trial in terms of design and procedures (such as recruitment rate, retention, safety of intravenous 1 gm of TXA, sample size verification) and assess the efficacy of TXA on the ovarian reserve and intra-operative blood loss by comparing mean difference of AMH levels between TXA and control groups at pre- and 3 months post-surgery.

The recruitment and successful completion rates were 95% and 100%. Baseline characteristics were similar in the two groups. The mean difference of serum AMH levels (pre- and 3 months post-surgery) between the TXA and control groups was not significantly different. When performing a subgroup analysis, the mean difference of AMH levels (pre- and 3 months post-surgery) seemed to be higher in the bilateral than in the unilateral ovarian cyst group but not significantly different. Operating time was significantly longer in bilateral than in unilateral cysts. No post-operative complications or adverse effects were found. © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. * Correspondence: [email protected] 2Reproductive Endocrinology and Infertility Unit, Department of Obstetrics and Gynaecology, Faculty of Medicine Ramathidodi Hospital, Mahidol University, Praram 6 Rd., Phayatai, Bangkok 10400, Thailand Full list of author information is available at the end of the article Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 https://doi.org/10.1186/s40814-021-00907-y

The full randomized controlled trial for evaluating effects of TXA administration during laparoscopic cystectomy for endometrioma on ovarian reserve was shown to be feasible. Several modifications should be added for improving feasibility, for example, increasing the TXA dose, modifying TXA administration, focusing on either patients with unilateral or bilateral ovarian cysts, and exploring other outcome measures, e.g., surgeons ’ satisfaction. Trial registration: Thai Clinical Trials Registry, TCTR20190424002, Registered 24 April 2019.

Anti-fibrinolytic Agents, Anti-Mullerian hormone, Endometriosis, Ovarian reserve, Tranexamic acid Key messages regarding feasibility /C15What uncertainties existed regarding the feasibility of this study? Uncertainty regarding recruitment and retention of patients who have ovarian endometriotic cysts undergoing laparoscopic cystectomy and administration of tranexamic acid to preserve ovarian function. Uncertainty regarding the ability of patients to complete the study. /C15What are the key feasibility findings? The recruitment and retention of patients was feasible and showed zero rate of incompleteness of the study /C15What are the implications of the feasibility findings for the design of the main study? Modifications of study design would be needed for conducting the full randomized controlled trial. Many suggestions for the next study include a probable increase in the dosage of tranexamic acid, a study on similar patients with either unilateral or bilateral ovarian cyst, and investigation of other outcome variables.

Ovarian endometriosis (endometriomas) is a common gynecological disease that occurs up to 10% of repro- ductive women and the prevalence of disease is up to 20 to 50% in infertile women [ 1–3]. The clinical presenta- tions include pelvic pain, progressive dysmenorrhea, dyspareunia, and subfertility. The presence of endome- triomas has the potential to destroy healthy ovarian tis- sues that leads to decreased ovarian function [ 4], problems with ovulation [ 5], and primary ovarian insuffi- ciency [ 6]. The most effective treatment for endometrio- tic cyst is controversial. The first-line management of endometriotic cyst, a diameter larger than 3 cm, is a lap- aroscopic ovarian cystectomy [ 7]. Moreover, manage- ment of endometrioma larger than 3 cm in women who have an infertility problem should consist of ovarian cystectomy prior to assisted reproductive technologies to improve pelvic pain or help perform the oocyte retrieval procedure without difficulties [ 8]. Although laparoscopic ovarian cystectomy provides the lowest recurrence and the highest chance of spontaneous pregnancy rate, risk of significant ovarian injury can occur. Ovarian injury is thought to be caused by loss of healthy ovarian follicles during surgery and inflammation caused by surgical trauma or vascular injury. Recent data have demon- strated that surgical treatment of endometriotic cyst have an adverse effect on ovarian reserve [ 9]. Inadvertent removal of normal ovarian tissue is one of the reasons for the reduction in ovarian reserve during cystectomy [10]. Serum anti-Müllerian hormone (AMH) is the most reliable and practical measurable marker for ovarian re- serve [ 11]. This hormone reflects the number of high- quality oocytes within the ovaries. AMH is secreted by granulosa cells in women of reproductive age. Several studies have demonstrated a decrease in AMH levels after laparoscopic cystectomy of endometriomas [ 12– 14]. In our study, AMH was used to evaluate ovarian re- serve. The advantage of AMH over other ovarian serum markers is fairly constant levels, and hormone levels can be measured on any day of the menstrual cycle. AMH levels are reliable for predicting fertility and helping phy- sicians identify women at risk of premature ovarian in- sufficiency [ 15, 16]. Many gynecologists try to find strategies to preserve ovarian function. We hypothesized that if a decrease in blood loss during surgery occurs, the surgeon could view the operative field clearly and could per- form the operation smoothly with less use of bipolar coagulation. As a result, vascular and healthy ovarian tissue damage would be decreased. In the present study, we use tranexamic acid (TXA) as a pharmaco- logical tool for reducing bleeding during surgery. TXA has been widely used during surgery to decrease bleeding and wound complications [ 17–19]. The rec- ommended standard dose is 1 g every 6 to 8 h in general fibrinolysis [ 20] .H o w e v e r ,t h ed o s ec o u l db e increased in case of excessive bleeding but should not exceed a maximum daily dose of 4 g [ 21]. The objectives of this study were to evaluate the feasi- bility of conducting a definitive trial in terms of design and procedures (such as recruitment rate, retention, Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 2 of 10 safety of intravenous 1 g of TXA, and sample size verifi- cation) and assess TXA efficacy on ovarian reserve and intra-operative blood loss by comparing the mean differ- ence of AMH levels between TXA and control groups. AMH was measured pre- and at 3 months post-surgery.

This study was a double-blind randomized controlled trial (RCT) conducted between May 2019 and November 2020. The study was approved by the Ethical Clearance Committee on Human Related to Researches Involving Human Subjects and Faulty of Medicine Ramathibodi Hospital Mahidol University (No. MURA2019/245) and was registered on the Thai Clinical Trial Registry (TCTR). This study was conducted in accordance with the 1964 Helsinki Declaration. Reproductive women ages 19 –45 years who were plan- ning to undergo laparoscopic cystectomy for unilateral or bilateral endometriotic cysts were invited to partici- pate in the study. Inclusion criteria included several pa- rameters: (1) unilateral/bilateral endometriotic cyst with typical ultrasonography characteristics [ 22], (2) ovarian cyst size 3 –10 cm, (3) no previous use of oral hormones 3 months prior to the study, (4) no history of taking depot-medroxyprogesterone acetate or gonadotropin re- leasing hormone agonist within 9 months prior to the study, and (5) willingness to participate in the study. Ex- clusion criteria included several parameters: (1) preg- nancy and post-menopausal status, (2) history of allergy or contraindications to TXA, (3) underlying disease, such as thromboembolic disease, which contradicts the use of TXA, (4) pre-operative AMH level < 0.5 ng/ml, and/or (5) history of previous ovarian surgical interven- tion. Eligible participants were enrolled in the present study and signed the consent forms. The participants were randomly assigned either: (1) TXA and (2) un- treated or control. Blocks of four were randomized with a 1:1 ratio by an independent nurse and concealed in a labeled envelope. Serum samples were collected before laparoscopic ovarian cystectomy. For the intervention group, TXA 1 g intravenously was administered by anes- thesiologists within 10 min before making skin incision. Surgeons were blinded to the participant groups. Lap- aroscopic surgery was performed with the standard op- erating procedure by the endoscopic staff in the Ramathibodi hospital. All surgeons ( n = 5) had compar- able surgical skills and experience with laparoscopy. Briefly, after general anesthesia was administered, the participants laid in the Trendelenburg position. The pri- mary trocar was placed at the umbilicus with 2 to 3 accessory ports. Ovarian cystectomy was initiated by an incision over the wall of ovarian cyst through the cortex. The cyst wall was mobilized by sharp and blunt dissec- tion and removed from the ovarian cortex. The inner ovarian stroma was coagulated with bipolar electro- cautery (20 –30 W current) to achieve satisfactory hemostasis and approximation. The ovarian cortex was closed with an absorbable suture (2 –0o r3 –0). Blood loss was calculated by anesthesiologists as the difference between the total amounts of suction and irrigation. All intra- and post-operative complications occurring within 3 months of the operation were recorded. The partici- pants were scheduled for follow-up appointments at 3 months post-surgery. Sera were collected for measure- ment of post-surgery AMH levels. Outcomes The primary objective of this study was to evaluate the feasibility of conducting a definitive trial in terms of sev- eral parameters: (1) recruitment rate, (2) successful com- pletion of the study procedures, (3) safety of intravenous 1 g of TXA, and (4) verification of the sample size calcu- lation for the full RCT using intravenous 1 g of TXA on ovarian function preservation in patient who undergoing ovarian cystectomy. Recruitment and successful comple- tion rate observed in the pilot which are considered feas- ible for the full RCT were not less than 90% of all eligible patients and 95% of all enrolled patients, respect- ively. Safety of intravenous 1 g of TXA is defined as no serious adverse drug reaction (ADR). Serious ADR de- noted as any unfavorable medical occurrence that at 1 g TXA: (i) resulted in death; or (ii) was life-threatening; or (iii) prolonged hospital stay; or (iv) resulted in significant handicap; or (v) required medical or surgical interven- tion to prevent a permanent defect of a body function or structure; or (vi) was a malignancy or a congenital anomaly [ 23]. The secondary objectives included assessments of TXA efficacy on ovarian reserve and intra-operative blood loss by comparing mean difference of AMH levels between TXA and control groups. AMH was assessed pre-operatively and at 3 months post-surgery. AMH was quantified using an electrochemiluminescence assay (ECLIA; Elecsys® AMH assay, Roche Diagnostics) by a technician who was unaware of participant allocation. Sample size The intended sample size for the present study had been estimated using a formula calculated based on the prob- ability of observing problems occurring in target study subjects with a chosen level of confidence. P(x >0 )=1 – (1 − π)n. Where x indicates as number of participants (of the n participant). The formula is: n = ln(1 − γ)/ln(1 − π)i f π designates the problem probability and γ de- notes certain threshold of confidence by 100% × γ (such as 95% CI, γ is 0.95) [ 24, 25]. The calculator is available at http://www.pilotsamplesize.com). Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 3 of 10 The lowest recruitment rate approximately 5 –10% with at 95% confidence interval was used to calculate for the present study. Twenty-eight to 58 participants were needed for the unsuccessful recruitment rate of 5 –10%. We chose 40 participants to enroll in the present study and estimated that it would require 15 months, includ- ing a 3-month follow-up, to complete the study. Statistical methods Software program SPSS version 21.0 (SPSS Inc., Chicago, USA) was used for statistical analysis. The Pearson ’s chi- square and Student ’s t tests were applied to compare categorical and continuous parametric data, respectively. The Mann –Whitney test was used to compare nonpara- metric continuous data, that is, serum AMH levels be- fore and after surgery and the difference in AMH levels (pre- and 3-month post-surgery). P values < 0.05 were considered to be statistically significant. The median dif- ference and 95% confidence interval (CI) of difference were calculated by Stata Statistical Software: Release 15.0 (College Station, TX, USA) and Hodges-Lehmann median methods. ( https://www.real-statistics.com/non- parametric-tests/mann-wh itney-test/mann-whitney- median-confidence-interval/)

Recruitment, recruitment rate, and the successful completion of the study procedures Enrollment took place from May 2019 through Au- gust 2020, and the 3-month follow-up was completed in November 2020. The timeline for recruitment was delayed by 4 months because of the start of the cor- onavirus 2019 (COVID-19) pandemic in Thailand. The operations for benign conditions, which included laparoscopic cystectomy, were temporarily halted for 4 months in our hospital. Of the total 42 participants who were invited to participate in this study, 40 par- ticipants were recruited and randomized into two groups. The recruitment rate was 95%. All of them completed a 3-month follow-up, as shown in Fig. 1. We made a phone call to the participants if they missed the follow-up day and invited them to visit on the next day. The rate of successful completion of the study procedures was 100%. Fig. 1 Flow chart of the study Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 4 of 10 Baseline and outcome characteristics The baseline demographic characteristics of the partici- pants are presented in Table 1. The two groups were similar in mean age, body mass index, parity, the max- imum diameter of ovarian cyst, laterality of lesions, and American Society of Reproductive Medicine (ASRM) stage of endometriotic cyst. The surgical outcomes were compared in treatment and control groups. Estimated blood loss, post-operative complications, and length of hospital stay were all similar in the two groups. How- ever, operating time in TXA group was longer than in the control group. Pre-operative AMH levels were also similar between patients in the TXA and control groups (2.9 ± 1.5 and 2.4 ± 1.8 ng/ml, respectively) as shown in Table 2. At 3 months post-surgery, serum AMH levels of the TXA and control groups decreased significantly. Means difference of pre- and 3-month post-operative AMH of TXA and control groups were 0.89 (95% CI 0.39 to 1.38) ng/ml and 0.83 (95% CI 0.30 to 1.37) ng/ ml, respectively (Table 3). However, the mean difference of serum AMH level (pre-and 3-month post-surgery) be- tween the TXA and control groups was not significantly different (0.05; 95% CI − 0.65 to 0.76). The mean differ- ence in serum AMH level (pre-and 3-month post- surgery) was 0.7 ± 1.2 and 0.8 ± 1.0 ng/ml in the control and TXA groups, respectively (Table 2). No post- operative complications or adverse effects were found, and none of the participants required a blood transfusion. In our study, we analyzed the outcomes between uni- lateral and bilateral ovarian cysts. There were no signifi- cant differences in the mean difference of AMH levels (pre- and 3-month post-operation) between unilateral and bilateral ovarian cysts ( − 0.61; 95%CI − 1.32 to 0.11). Moreover, operating time was significantly longer in patients with bilateral ovarian cysts than those with unilateral ovarian cysts, as shown in Table 4. We also analyzed subgroups consisting of pre- and 3-month Table 1 Baseline characteristics Characteristics Tranexamic acid (n = 20) mean +S Do r n (%) Control (n = 20) mean +S Do r n (%) Age (years) 30.6 ± 4.6 32.3 ± 4.9 Body mass index (kg/m 2) 20.2 ± 2.5 20.6 ± 3.7 Parity, n (%) Nulliparous 19 (95%) 19 (95%) Parous 1 (5%) 1 (5%) Maximum diameter of ovarian cyst (cm) 5.8 ± 1.8 5.4 ± 1.4 Number of ovarian cyst side, n (%) Unilateral 14 (70%) 12 (60%) Bilateral 6 (30%) 8 (40%) ASRM stage, n (%) Stage 3 15 (75%) 11 (55%) Stage 4 5 (25%) 9 (45%) Note: ASRM American Society of Reproductive Medicine, SD standard deviation Table 2 Outcomes between treatment and control groups Tranexamic acid (n = 20) mean + SD or median (IQR) Control (n = 20) mean + SD or median (IQR) Mean or median difference 95% CI Pre-operative AMH (ng/ml) 2.9 ± 1.5 2.4 ± 1.8 0.50 − 0.56 to 1.56 Post-operative AMH (ng/ml) 2.0 ± 1.5 1.6 ± 1.1 0.40 − 0.44 to 1.24 Difference of AMH level (ng/ml) a 0.8 ± 1.0 0.7 ± 1.2 0.10 − 0.61 to 0.81 Operative time (min) 130.0 (82.5) 120 (106.3) 0 − 35.00 to − 30.00 Estimated blood loss (ml) 50.0 (50.0) 65.0 (150) 0 − 50.00 to 0 Length of hospital stay (days) 1.8 ± 0.4 1.9 ± 0.4 − 0.10 − 0.36 to 0.16 Note: AMH anti-Müllerian hormone, IQR interquartile range, SD standard deviation, CI confidence interval aDifference of AMH level = pre-operative AMH-post-operative AMH *The test of significance for pilot trials is not helpful as such studies are not designed for statistical significance Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 5 of 10 post-surgery AMH levels by comparing control and TXA groups for each unilateral and bilateral ovarian cyst group. The mean difference of AMH levels in the TXA and control groups in women with unilateral ovarian cyst was not significantly different (0.06, 95%CI − 0.86 to 0.98). Operating time and blood loss were not signifi- cantly different between TXA and control groups as shown in Table 5. The mean difference in AMH levels in the TXA and control groups in women with bilateral ovarian cyst was not significantly different (0.22, 95%CI − 0.98 to 1.42). Operating times and blood loss were also not significantly different between TXA and control groups as shown in Table 6. Verification of sample size calculation for the full RCT We then performed the statistical calculation for power from our results using the mean difference between pre- and post-surgery AMH levels and SD for TXA and con- trol groups were 0.8 ± 0.1 and 0.7 ± 1.2, respectively. The power was only 4.2% ( www.openepi.com). We also calcu- lated the sample size for future full-scale randomized con- trol studies addressing the effects of TXA on ovarian reserve during laparoscopic ovarian cystectomy for endo- metrioma with the formula comparing two means. Our revised sample size calculation verified 1915 experimental and 1915 control participants to allow for rejection of the null hypothesis with probability (power) 0.8 and type I error probability of 0.05. With a 10% allowance for drop- outs, the total sample size would be 4214.

The present pilot study demonstrated that conducting a large randomized double-blind controlled trial would be feasible with some modifications. Our results do not rule out the benefit of the administration of intravenous TXA immediately before laparoscopic cystectomy in pa- tients with endometriotic cysts. TXA seems beneficial for blood loss when we analyzed subgroups of unilateral and bilateral ovarian cyst patients. However, several modifications should be made to improve feasibility, such as increasing the TXA dosage, modifying TXA ad- ministration, studying women either with unilateral or bilateral ovarian cysts, increasing the follow-up interval, and examining other outcomes, e.g., ease of surgery and surgeon’s satisfaction. The present study ’s recruitment and retention rate was high because TXA administration is quite a safe intervention and could be theoretically beneficial to pa- tients. The follow-up time after surgery is short, and follow-up visits are often needed to prevent the recur- rence of the disease. These factors could increase the willingness of patients to come back for follow-up ap- pointments. The delay in recruitment in the present study was unavoidable because of the global pandemic. The laparoscopic cystectomy for endometriotic cysts caused a decrease in ovarian reserve at 3 months after surgery. Results from our study were similar to the others [ 26–28]. The proposed mechanisms for decreas- ing ovarian reserve include inadvertent removal of Table 3 Outcomes between pre- and post-operative AMH levels Pre-operative AMH mean +S D (ng/ml) (n = 20) Post-operative AMH mean +S D (ng/ml) (n = 20) Mean difference 95% CI Tranexamic acid 2.9 ± 1.5 2.0 ± 1.5 0.90 − 0.06 to 1.86 Control 2.4 ± 1.8 1.6 ± 1.4 0.80 − 0.23 to 1.83 Note: AMH anti-Müllerian hormone, SD standard deviation, CI confidence interval *The test of significance for pilot trials is not helpful as such studies are not designed for statistical significance Table 4 Outcomes between women with bilateral and unilateral ovarian cysts Unilateral ovarian cyst (n = 26) mean + SD or median (IQR) Bilateral ovarian cyst ( n = 14) mean + SD or median (IQR) Mean or median 0difference 95% CI Difference of AMH level (ng/ ml)a 0.5 ± 1.1 1.2 ± 1.0 − 0.7 − 1.41 to 0.01 Estimated blood loss (ml) 50 (35) 100 (150) − 50.00 − 100.00 to 0 Length of hospital stay (days) 2 (0) 1.9 (0) 0.00 0 to 0 Operation time (min) 124.4 ± 38.8 181.6 ± 71.3 − 57.2 − 92.26 to − 22.14 Note: AMH anti-Müllerian hormone, SD standard deviation, CI confidence interval aDifference of AMH level = pre-operative AMH-post-operative AMH *The test of significance for pilot trials is not helpful as such studies are not designed for statistical significance Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 6 of 10 normal ovarian tissue during cystectomy and thermal in- jury. Ovarian parenchymal tissue and primordial follicle of normal ovarian tissue were observed in the specimens collected from the surgeries [ 29, 30]. Electrocauteriza- tion, such as bipolar electrosurgery, which is often used to control bleeding during laparoscopic cystectomy, could damage ovarian follicles [ 31]. Several strategies have been reported to prevent ovarian reserve decline after laparoscopic ovarian sur- gery, including different sur gical techniques, chemical agents, and medications [ 32–34]. Ovarian cystectomy reduced ovarian reserve after surgery more than ovar- ian ablation (or vaporization) and deroofing; however, cyst recurrence was found more often in patients treated with ovarian ablation and deroofing than cyst- ectomy [ 26, 35]. A systematic review involving 1047 patients demonstrated that laparoscopic ovarian su- ture preserved ovarian function more than bipolar electrosurgery did. A hemostatic sealant agent was su- perior to bipolar coagulation. Ultrasonic electrosur- gery was equal to bipolar coagulation [ 36]. However, studies of the effect of TXA on ovarian reserve in laparoscopic cystectomy, have not been previously reported. TXA is widely used to decrease blood loss in many sit- uations. TXA (trans-4-(Aminomethyl) cyclohexanecar- boxylic acid) is a synthetic derivative of the amino acid lysine that competitively inhibits the activation of plas- minogen to plasmin and is a competitive inhibitor of tissue plasminogen activator. It inhibits the lysine- binding sites of plasminogen, resulting in inhibition of plasminogen activation and fibrin binding to plasmino- gen and, therefore, leads to impairment of fibrinolysis. High doses of TXA reduce plasmin formation [ 37]. Many strong pieces of evidence demonstrate that TXA causes a reduction in blood loss during major surgery. A large systematic review of several RCTs in 10,488 surgi- cal patients comparing TXA/no TXA administration (placebo) demonstrated that TXA contributes to a re- duction in approximately one-third of blood transfusion requirements [ 19]. The dosage of TXA for local fibrin- olysis treatment is 0.5 to 1 g (equivalent to 15 mg/kg) by intravenous injection every 6 to 8 h while the dosage for general fibrinolysis treatment is a single dose of 1 g or 10 mg/kg by intravenous injection [ 38]. The meta- analysis by Heyns et al. suggested that the most frequently used single dose for a reduction of peri- operative estimated blood loss in several types of oper- ation was 15 mg/kg [ 39]. A study by Abbasi et al. compared two doses of TXA, i.e., 5 and 15 mg/kg dur- ing sinus endoscopy surgery [ 40]. The study demon- strated that the administration of TXA 15 mg/kg reduced more blood loss and more surgeons satisfied surgical field than those of TXA 5 mg/kg. Therefore, t h es i n g l ed o s eo fT X A1g( e q u i v a l e n tt o1 5t o2 0m g / kg) was selected to explore in the present study. How- ever, a single dose of TXA up to 100 mg/kg had been reported in coronary artery surgery [ 41]. Table 5 Outcomes between treatment and control group in women with unilateral ovarian cyst Tranexamic acid ( n = 14) mean +S Do r median (IQR) Control (n = 12) mean +S Do r median (IQR) Mean or median difference 95% CI Difference of AMH level (ng/ml) a 0.6 ± 1.0 0.5 ± 1.2 0.10 − 0.79 to 0.99 Estimated blood loss (ml) 50 (18) 77.5 (60.8) 0 − 30.00 to 10.00 Length of hospital stay (days) 2 (0) 2 (0) 0 0 to 0 Operation time (min) 131.0 ± 38.0 116.7 ± 39.9 14.30 − 17.27 to 45.97 Note: AMH anti-Müllerian hormone, SD standard deviation, CI confidence interval aDifference of AMH level = pre-operative AMH-post-operative AMH *The test of significance for pilot trials is not helpful as such studies are not designed for statistical significance Table 6 Outcomes between treatment and control groups in women with bilateral ovarian cysts Tranexamic acid (n =6 ) mean + SD or median (IQR) Control (n =8 ) mean + SD or median (IQR) Mean or median difference 95% CI Difference of AMH level (ng/ml) a 1.3 ± 1.0 1.1 ± 1.0 0.22 − 0.98 to 1.42 Estimated blood loss (ml) 100 (75) 150 (175) − 50.00 − 150.00 to 50.00 Length of hospital stay (days) 2 (0) 2 (0) 0.00 − 1.00 to 1.00 Operation time (min) a 156.7 ± 60.9 200.4 ± 76.5 − 43.71 − 126.58 to 39.16 Note: AMH anti-Müllerian hormone, SD standard deviation, CI confidence interval aDifference of AMH level = pre-operative AMH-post-operative AMH *The test of significance for pilot trials is not helpful as such studies are not designed for statistical significance Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 7 of 10 The present study did not demonstrate any beneficial effect of TXA for reducing blood loss. Blood loss from the use TXA was less than that in control but not sig- nificantly different (50 vs 60 ml). The possible explan- ation for the different results when compared to the previous meta-analysis could be the smaller amount of blood loss in the present study. Because the amount of blood loss was small (only 50 –60 ml), consequently, the difference of amount blood loss between TXA and the control group was even smaller and difficult to assess precisely. Moreover, the laterality of the ovarian cyst could have interfered with the results. In general, pa- tients with unilateral ovarian cystectomy showed less blood loss during surgery than bilateral procedures. Our study was the first report to evaluate the benefit of TXA on ovarian reserve, which administered before laparoscopic ovarian cystectomy by measured mean dif- ference AMH level preoperative and 3 months after sur- gery. We did not find that intra-operative TXA can help preserve ovarian function. Although the sample size of the present study was small, our revised sample size cal- culation verified 4214 participants to allow for rejection of the null hypothesis. Therefore, it is very unlikely that future study could be conducted with an enormous sam- ple size, even studying in multi-centers. Ovarian laterality is a significant factor impacting ovar- ian reserve in patients undergoing cystectomy. Based on previous studies, bilateral cystectomy was statistically as- sociated with a significant reduction in AMH levels and ovarian reserve compared to the unilateral cystectomy group [ 28, 42]. However, our study demonstrated a de- crease in serum AMH levels post-surgery more in the bilateral than in the unilateral cysts, but these results did not present a significant difference. This finding could have occurred because the sample size was not calcu- lated according to laterality. Few side effects of TXA have ever been reported [ 37], which is consistent with our study. The strengths of the study were evaluated. Our study was a pioneer and a double-blinded RCT study, and sur- geons with the same experience levels performed the surgery. Our study had limitations, including short-term follow-up and no assessment of other ovarian reserve markers (follicle-stimulating hormone [FSH], inhibin-B) or sonographic markers. The present study results will help guide future studies of ovarian reserve reduction prevention during ovarian surgery in terms of optimal dosage and administration methods of tranexamic acid, laterality of ovarian cysts, and other outcome variables, e.g., surgeons ’ satisfaction and ease of the operation.

The results from the present study support the feasibility of conducting the full RCT for the intravenous TXA administration during laparoscopic cystectomy for endo- metrioma. Several modifications should be added to achieve the full RCT, such as increasing the TXA dose, focusing on patient subgroups (either with unilateral or bilateral ovarian cysts), exploring surgeons ’ satisfaction, and follow-up periods longer than 3 months. Abbreviations ASRM: American Society of Reproductive Medicine; AMH: Anti-Müllerian hormone; CI: Confidence interval; COVID-19: Coronavirus 2019; ECLIA: Electrochemiluminescence assay; FSH: Follicle stimulating hormone; PPH: Post-partum hemorrhage; RCT: Random controlled trial; STD: Standard division; TXA: Tranexamic acid; TCTR: Thai Clinical Trial Registry

We thank all faculty of Department of Anaesthesiology for their assisting in the study. We also thank nurses at the gynecologic out-patient clinic for their support in management of patients. Authors’ contributions PA, WI, and AS contributed in the study design, conception, planning, and implementation strategy. PA and MA contributed in data collection and management and recruitment strategy. PA, SL, WH, OV, ST, and KP contributed in data collection. SV contributed in the data analysis and interpretation. PA and AS contributed in the writing the manuscript. All authors have read and approved the final manuscript. Funding This research is supported by Faulty of Medicine Ramathibodi Hospital Mahidol University. Availability of data and materials The datasets generated and/or analyzed during the current study are available from the corresponding author on request. Declarations Ethics approval and consent to participate Our study protocol was reviewed and approved by the Ethical Clearance Committee on Human Related to Researches Involving Human Subjects and Faulty of Medicine Ramathibodi Hospital Mahidol University (No. MURA2019/245). Written informed consent was obtained for all participants before the initiation of the study procedures. Consent for publication Not applicable Competing interests The authors declare that they have no competing interests. Author details 1Department of Obstetrics and Gynaecology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand. 2Reproductive Endocrinology and Infertility Unit, Department of Obstetrics and Gynaecology, Faculty of Medicine Ramathidodi Hospital, Mahidol University, Praram 6 Rd., Phayatai, Bangkok 10400, Thailand. 3Gynecologic Oncology Unit, Department of Obstetrics and Gynaecology, Faculty of Medicine Ramathidodi Hospital, Mahidol University, Bangkok 10400, Thailand. 4Department of Anesthesiology, Faculty of Medicine Ramathidodi Hospital, Mahidol University, Bangkok 10400, Thailand. 5Department of Pathology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand. 6ASEAN Institute for Health Development, Mahidol University, Nakorn Pathom 73170, Thailand. Akkaranurakkul et al. Pilot and Feasibility Studies (2021) 7:171 Page 8 of 10 Received: 28 December 2020 Accepted: 27 August 2021

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