Exploration of standard dosage for GnRH antagonist protocol and dosage adjustments after premature luteinizing hormone surge

HAN Zhong-yi, WU Ting-ting, MA Yan-lin

Department of Reproductive Medicine, The First Affiliated Hospital of Hainan Medical University

Hainan Provincial Key Laboratory for Human Reproductive Medicine and Genetic Research

Hainan Provincial Clinical Research Center for Thalassemia

Key Laboratory of Reproductive Health Diseases Research and Translation (Hainan Medical University), Ministry of Education Haikou Key Laboratory for Preservation of Human Genetic Resource, Haikou 571101, China

Keywords:

ABSTRACT The gonadotropin-releasing hormone (GnRH) antagonist protocol has emerged as an efficacious alternative to the GnRH agonist protocol for controlled ovarian hyperstimulation(COH) during in vitro fertilization (IVF) cycles, and has been demonstrated applicability in infertile female patients with diverse ovarian responses.While the clinical implementation of the antagonist COH protocol has achieved widespread consensus, opportunities for refinement persist.Therefore, this review article focuses on the advantages and disadvantages of GnRH antagonist protocol, the selection of optimal standard doses, and the strategies for adjusting antagonist doses after the premature luteinizing hormone (LH) surge, aiming to provide more reasonable and scientific recommendations for the application of this scheme.

1.Introduction

Since the birth of the first successful “test-tube baby”, assisted reproductive technologies in humans have rapidly developed.Considering that in natural cycles, patients have a low number of retrieved oocytes and low pregnancy rate, and follicular development and maturation cannot be precisely controlled, ovarian stimulation protocols emerged in the 1980s.In 1986, Diamond et al.systematically applied an ovarian stimulation protocol using clomiphene citrate (CC) and human menopausal gonadotropin(hMG) to patients undergoing in vitro fertilization and embryo transfer (IVF-ET), achieving good results in ovulation induction[1].Subsequently, during continuous optimization processes, various protocols were developed, including gonadotropin-releasing hormone (GnRH) agonist protocol, GnRH antagonist protocol, mild stimulation protocol, and high progesterone protocol.Currently,GnRH antagonist protocol have been widely utilized in clinical practice.However, certain clinical issues associated with it, such as the selection of the optimal standard dosage for the antagonists, still remain controversial.On the other hand, the premature luteinizing hormone (LH) surge refers to the endogenous LH surge that occurs before the maturation of follicles or the administration of trigger medication during controlled ovarian hyperstimulation (COH), with diagnostic criteria of LH ＞10 IU/L and/or LH level greater than 2-2.5 times the baseline value[2].According to relevant studies, the incidence of premature LH surge can be reduced to 2% with the use of GnRH agonist protocol, whereas the incidence was relatively higher with the use of GnRH antagonist protocol[3].The reason for this may be related to the increase in estradiol (E2) level and the enhancement of positive feedback due to excessive or rapid follicular development, or it may be due to antagonist resistance.The appearance of premature LH surge can lead to asynchronous development of the nucleus and cytoplasm of oocytes, affecting the quality of oocytes and embryos.It can also cause luteinization of follicles, elevation of progesterone level, and adverse effects on the receptivity of the endometrium[4].Currently, some scholars believe that after the occurrence of premature LH surge during a cycle,the pregnancy outcome of the cycle can be salvaged by adjusting the antagonist dose, but there is still a lack of consistent standards and consensus.This article aims to summarize the current status of related researches both domestically and internationally, and provide corresponding insights and recommendations for the abovementioned issues.

2.Analysis of the Benefits and Drawbacks of GnRH Antagonist Protocol

GnRH antagonists act directly by competitively blocking GnRH receptors.The current third-generation GnRH antagonists used in clinical practice include Cetrorelix and Ganirelix, which cause fewer allergic reactions and are associated with higher overall patient comfort compared to earlier generations of antagonists[5].

2.1 Advantages of Antagonist Protocol

Compared to GnRH agonist protocol, antagonist protocol offers several advantages.First, it has a shorter medication duration and can avoid the ovarian cyst formation induced by the “flare-up”effect of GnRH agonists[6].Second, GnRH antagonists can rapidly inhibit the secretion of endogenous pituitary gonadotropins, possess reversibility and relatively short drug half-life.The reversibility is beneficial for the prompt recovery of pituitary function and enables GnRH agonists to serve as trigger medication in GnRH antagonist protocol, thereby significantly reducing the incidence of Ovarian Hyperstimulation Syndrome (OHSS)[7].Third, antagonist protocol has shorter treatment duration and lower average treatment costs than agonist protocol, and thus, is associated with higher patient acceptance.

2.2 Disadvantages of Antagonist Protocol

The current limitations of GnRH antagonists include longer learning curve for clinicians[3,8], lower oocytes yield compared to GnRH agonist protocol, and lower fresh cycle embryo transfer success rate[9].Some studies suggested that the use of GnRH antagonists may have a certain impact on endometrial receptivity, as they are derivatives of GnRH and can also bind to GnRH receptors in endometrial cells in addition to their role in the neuroendocrine system[10].GnRH antagonists can regulate the physiological function of the endometrium through multiple pathways, including modulation of the pituitary-ovarian axis, direct action on the uterus, paracrine and autocrine pathways, etc[11].Some studies had found that GnRH antagonists can affect endometrial receptivity by regulating the expression of factors such as S100P, CKB, TNF-α,etc[12-14].Other studies suggested that GnRH antagonists can reduce the synthesis of growth factors, thereby affecting endometrial development, reducing endometrial receptivity, and impacting the success rate of fresh embryo transfer[15].Additionally, the use of GnRH antagonists may generate abnormal inflammatory factors,which can affect embryo implantation and clinical pregnancy rate,and this effect may be dose-dependent, with higher doses resulting in more adverse effects on embryo implantation[16].Future research may focus on selecting appropriate doses of GnRH antagonists and developing endometrial receptivity-targeted drugs based on molecular biology to improve the pregnancy outcomes of patients receiving GnRH antagonist protocol.

3.Optimal Standard Dosage Selection of GnRH Antagonists

The GnRH antagonist protocol includes single-dose and multipledose regimens.The single-dose protocol involves a one-time high-dose injection of 3mg GnRH antagonist on day 7 of ovarian stimulation, which is less commonly used in clinical practice.In contrast, the multiple-dose regimen consists of fixed and flexible protocols.The commonly used dose of GnRH antagonist is 0.25 mg/d, but this dose may not be suitable for all patients.As GnRH receptors are present in the ovaries, uterus, breast, and some malignant cells[17], inappropriate doses of antagonists may cause non-specific reactions.For instance, commonly used antagonists like Cetrorelix exhibit dose-dependency, where increasing doses may result in adverse effects such as decreased endometrial receptivity,embryo implantation rate and pregnancy rate.[18,19].

Many research centers had attempted to optimize pregnancy outcomes by adjusting the use of GnRH antagonists.A retrospective study conducted by Liu et al.demonstrated that among 256 patients with LH level below 4 IU/L, there was no significant difference in the number of retrieved oocytes and number of high-quality embryos between the group receiving GnRH antagonist and the group not receiving GnRH antagonist.However, the clinical pregnancy rate and ongoing pregnancy rate were significantly higher in the group not receiving GnRH antagonist.Furthermore, no cases of cycle cancellation due to premature LH surge were observed in the group not receiving GnRH antagonist.The use of GnRH antagonist may potentially further decrease LH level in patients with LH level below 4 IU/L, thereby impacting pregnancy outcomes[20].Based on these findings, they launched a prospective study that using LH level as an indicator for adding antagonists to patients with normal ovarian response and adjusted the antagonist dosage according to LH level[21].Currently, this study is still ongoing.

3.1 Low-dose GnRH Antagonist Protocol

Tiboni et al.’s early prospective study showed that both low-dose(0.125 mg/day) and standard-dose (0.25 mg/d) GnRH antagonists could suppress premature LH surge, and there was no significant difference in clinical pregnancy rate and live birth rate between the two groups[22].In recent years, a retrospective study has indicated that low-dose (0.125 mg/d) and standard-dose (0.25 mg/d) GnRH antagonist treatment have comparable treatment outcomes[23].Another retrospective study proposed a flexible low-dose regimen(initial dose of antagonist set at 0.125 mg/d, and adjustment to 0.25 mg/d when LH ＞ 10 IU/L during the ovulation induction process),which found that the fertilization rate in the flexible antagonist group was lower than that in the fixed standard-dose group, but there was no significant difference in clinical pregnancy rate, early miscarriage rate, and ongoing pregnancy rate between the two groups[24].Xu et al.’s clinical randomized controlled study also showed that in ovulatory women with normal ovarian reserve, the use of low-dose GnRH antagonist protocol (initial dose of antagonist every other day at 0.25 mg), compared with the standard dose (initial dose of 0.25 mg/d), had no significant difference in the incidence of premature LH surge and clinical pregnancy rate[15].Although these studies had generally small sample sizes and were mostly single-center studies, they all demonstrated the clinical value of low-dose GnRH antagonist protocol.

Some scholars believed that the application guidelines for GnRH antagonists in China were mostly based on research conclusions from Western countries, where the height and weight of women differ significantly from those in Asia.Therefore, there is speculation that low-dose antagonist regimens may be more suitable for Asian women.Al-Inany et al.found that serum concentrations of GnRH antagonists were negatively linearly correlated with body weight in normal women with BMI of 18-30 kg/m2.Therefore, lower doses of antagonists may be more reasonable for women with low body weight[25].To determine the minimum effective dose of GnRH antagonists in Asian women, Hsieh et al.compared the clinical outcomes of patients receiving different doses of Cetrorelix (0.15,0.2, and 0.25 mg/d) and found that 0.25 mg/d was still the minimum effective dose for low-weight (＜50 kg) Asian women[26].

Overall, the 0.25mg/d GnRH antagonist protocol is based on longer-term clinical trials and carries a high level of credibility,making it the preferred GnRH antagonist protocol currently available.Low-dose GnRH antagonist protocol may reduce treatment costs for patients and has promising prospects.However,large-scale prospective multicenter studies are still needed to confirm their clinical efficacy.

3.2 High-dose Antagonist Protocol

Several clinical studies reported the impact of high-dose antagonist protocols on patients.For instance, an early randomized controlled study examined the effect of different doses (0.0625 mg/d, 0.125 mg/d, 0.25 mg/d, 0.5 mg/d, 1.0 mg/d, or 2.0 mg/d) of Ganirelix on follicular development and sex hormone levels.The result indicated that as the dosage of antagonist medication increased, there was a downward trend in daily serum LH levels and E2 (estradiol) levels measured on the day of human chorionic gonadotropin (hCG)administration.Although high-dose antagonists have detrimental effects on cycle outcomes, the supplementation of follicle-stimulating hormone (FSH) can still achieve similar numbers of oocytes and embryos as the conventional antagonist protocol[27].Garcia-Velasco et al.proposed that the supplementation of recombinant LH can mitigate the adverse effects of excessive pituitary suppression caused by high-dose antagonists on cycle outcomes[28], providing new insights for antagonist-related researches.Prapas et al.randomized patients at risk of ovarian hyperstimulation syndrome (OHSS) into two groups: Group A received double dose of the antagonist the day before hCG administration, while Group B received standard dose of the antagonist.The results showed that the incidence of earlyonset moderate/severe OHSS was significantly reduced in Group A,indicating that the double dose of the antagonist the day before hCG administration can effectively reduce the incidence of OHSS in highrisk patients, and there were no significant differences in pregnancy rate, live birth rate, or early miscarriage rate between the two groups after fresh embryo transfer[29].

In summary, the flexible high-dose GnRH antagonist protocol can be used in certain special situations, such as preventing OHSS in patients at risk of ovarian hyperstimulation syndrome and preventing premature LH surge during ovulation induction.However, during the application of high-dose GnRH antagonist protocol, close attention should be paid to the changes in hormone levels during follicular stimulation, and external gonadotropin supplementation should be added timely to reduce the adverse effects of pituitary over-inhibition on follicular development, or antagonist dosage should be appropriately reduced according to hormone changes,while avoiding the adverse effects of high-dose antagonists on fresh cycle embryo transfer.At present, the routine dose of GnRH in our center is 0.25 mg/d, and when patients exhibit premature LH surge during ovulation induction, the single administration of antagonist medication may be increased by 0.125-0.5 mg, based on the patient’s follicular development and hormone levels, with timely adjustments made to the treatment plan.

Currently, the analysis of the standard dosage of GnRH antagonists in ovulation induction protocol is limited to small sample sizes and single-center clinical studies.Although the general framework of the standardized use of GnRH antagonist protocol has been established,clinicians still face various issues in practical applications.Therefore,more prospective, multicenter, and large-scale clinical studies are needed to address these issues and provide better treatment options for infertility patients.

4.Adjustment of the Antagonist Dosage after Premature LH Surge during Ovarian Stimulation

During COH, the occurrence of premature LH surge can have adverse effects on the pregnancy outcome of patients.Timely adjustment of antagonist dosage may help improve the pregnancy outcome of those cycles.A study indicated that in antagonist ovulation induction therapy for patients with ovarian hyperresponse,there were no significant differences in the number of retrieved oocytes and the rate of metaphase II (MII) oocytes between patients with premature LH surge and those without.However, the group without premature LH surge exhibited significantly higher rates of 2PN embryos, high-quality embryos, and clinical pregnancy rates following fresh embryo transfers.These findings confirmed the negative impact of premature LH surge on cycle outcomes[30].

In a study by Reichman et al., which included 10,809 GnRH antagonist cycles, they selected 37 cycles with premature LH surge and compared them with age-matched control group at a ratio of 1:50.They found that diminished ovarian reserve was the main risk factor for premature LH surge in GnRH antagonist cycles.Additionally, they proposed that increasing the dosage of GnRH antagonist after premature LH surge may reduce serum LH level and eliminate premature LH surge in some patients[31].In a case report by Nong et al., three patients who experienced premature LH surge during COH were able to control LH level by increasing the dosage of antagonist and timely triggering based on hormone changes and follicle size.All three patients successfully obtained oocytes[32].Another case report from China also indicated that increasing the antagonist dosage to 0.5mg/day in a patient who experienced premature LH surge led to reduction in LH level to 4.54 IU/L after one day of administration.Subsequently, the patient’s LH level remained within the range of 4 to 5 IU/L until the trigger day.Ultimately, a total of 19 oocytes were retrieved in this cycle, with 18 of them reaching the metaphase II (MII) stage[33].

Currently, in clinical practice, physicians typically consider escalating the dosage of antagonist medication to mitigate the elevated LH level in patients presenting with premature LH surge.However, in case where the premature LH surge cannot be effectively suppressed, a comprehensive evaluation of hormone levels, follicle count, and follicle size is crucial for determining the optimal timing to trigger ovulation and proceed with oocyte retrieval.Nonetheless,there is currently lack of high-quality clinical research providing definitive guidelines for the adjusting antagonist protocol in such cases.A clinical retrospective study conducted at our center has provided preliminary evidence suggesting appropriately increasing the dosage of antagonist medication in a single administration,instead of the premature triggering, may yield greater benefits for the patients with premature LH surge.We stratified the patients into three groups based on the increment of antagonist dosage: 0.125 mg,0.25 mg, and 0.375-0.50 mg.The group receiving 0.375-0.50 mg of additional antagonist was demonstrated higher rates of fresh embryo pregnancy, fresh embryo live birth, frozen embryo pregnancy,cumulative pregnancy, and cumulative live birth, however, these results have not yet reached statistical significance, possibly due to factors such as a limited number of cases.This study is still ongoing and further improvements are being made to enhance its outcomes.

5.Conclusions and Future Perspectives

In extensive clinical practice, it has been observed that the number of retrieved oocytes with GnRH antagonist protocol may be lower compared to GnRH agonist protocol.However, GnRH antagonist protocol have been shown to have similar clinical pregnancy rate and live birth rate as GnRH agonist protocol.Currently, the standard dosage for multi-dose GnRH antagonist protocol is 0.25 mg/d.Although several clinical studies with small sample sizes have suggested that lower dosage regimens can achieve comparable efficacy to standard regimens, further researches are needed to confirm their effectiveness.In cases of the cycles with premature LH surge or high ovarian response, the dosage of antagonist can be appropriately increased as needed.In the future, multicenter, largescale, prospective, randomized controlled trials are necessary to address these issues.

Authors’ contribution

Zhongyi Han: Conceptualized the research direction, selected the research topic, conducted literature review and organization, and wrote the paper.

Tingting Wu: Revised the paper.

Yanlin Ma: Reviewed the paper.