The Role of Manufacturing Quality of Human Chorionic Gonadotropin Injection in Empty Follicle Syndrome and Infertility Treatment Outcomes – Literature Review

Abstract

Globally 1 in 6 people are affected by infertility. 25-30% of subfertile females undergo subfertility treatment with ovulation induction. HCG trigger is done to induce ovulation by mimicking body’s natural luteinizing hormone (LH) surge to release mature egg about 36 hours post administration of required strength of HCG injection. HCG injection helps the eggs to complete process of final maturation, without which eggs may not get fertilisation, and even if fertilised may result in low quality embryo. HCG injection also helps stimulating corpus luteum to produce progesterone and improved uterine lining to enhance chances of implantation. Hence, the potency and effectiveness of HCG injection to produce sufficient serum HCG serum concentration, peak plasma concentration, area under curve (AUC) and other pharmacokinetics and pharmacodynamics is of high importance to achieve best results in ovulation induction cycles. A comprehensive data search was conducted on MedLine, PubMed, CINAHL with search words, “HCG Injection Quality”, “Quality of HCG Injection”, “Factors of EFS”, “HCG and EFS”, “HCG and Implantation”, “HCG and Progesterone”. Finally, 44 studies were selected based on publication year classification (between 2010 till 2024). The quality of HCG manufacturing, process of removal of impurities, resulting serum concentration, the time to peak plasma concentration, elimination time, is correlated with overall outcome of ovulation induction cycle and early pregnancy, as well as correlated with the risk of false empty follicle syndrome along with other factors discussed in the review.

Keywords

ovulation induction, empty follicle syndrome, ovarian stimulation, HCG injection quality, HCG and Implantation, HCG and Progesterone, HCG and EFS

Introduction

Empty follicle syndrome is a perplexing clinical phenomenon characterized by the failure to retrieve oocytes following controlled ovarian stimulation and human chorionic gonadotropin (hCG) triggering, despite adequate follicular development and appropriate hormonal responses (Castillo, García-Velasco and Humaidan, 2012).

This condition, estimated to affect 2–7% of IVF patients, presents significant challenges for both patients and clinicians (Castillo, García-Velasco and Humaidan, 2012). It is broadly categorized into genuine EFS, where optimal beta-human chorionic gonadotropin (β-hCG) levels are present post-injection, and false EFS, which is characterized by negligible β-hCG levels, often suggesting an injection error or a pharmaceutical issue (Luo, Xu and Hao, 2024). The latter can also arise from rapid metabolic clearance of hCG within the patient, underscoring the multifactorial nature of this distressing event (Vaiarelli et al., 2023). While patient-related factors such as aberrant folliculogenesis or rapid hCG metabolism contribute to EFS, the manufacturing quality of hCG injections warrants rigorous examination as a potential etiology (Leão and Esteves, 2014).

This review aims to explore the intricate relationship between the manufacturing quality of hCG injections and the incidence of EFS, dissecting how variations in formulation, purity, and stability might contribute to suboptimal follicular maturation or trigger failure (Luo, Xu and Hao, 2024). Specifically, this analysis will delve into how manufacturing inconsistencies or pharmacological abnormalities in commercially available hCG preparations could lead to insufficient biological activity, thereby mimicking or exacerbating EFS, implantation failure, and compromised luteal phase due lesser serum progesterone  post HCG injection (Castillo, García-Velasco and Humaidan, 2012). The distinction between genuine and false EFS is critical, as false EFS often arises from human error in administration or pharmacological concerns related to the hCG product itself, warranting a closer look at manufacturing standards (Castillo, García-Velasco and Humaidan, 2012).

METHODOLOGY:

A comprehensive search of databases, google, NIH, PubMed, is done for scientific literature including “HCG Injection Quality”, “Quality of HCG Injection”, “Factors of EFS”, “HCG and EFS”, “HCG and Implantation”, “HCG and Progesterone”. A total of 68 scientific papers were retrieved out of which 44 studies published between 2010 and 2024 are included in this literature review.

LITERATURE REVIEW DISCUSSION:

Given that the human chorionic gonadotropin (hCG) molecule is a glycoprotein comprised of alpha and beta subunits (Leão and Esteves, 2014), the integrity of its tertiary structure and post-translational modifications during the manufacturing process is paramount for its biological efficacy. This includes the appropriate glycosylation patterns and quaternary structure, which are crucial for binding to the luteinizing hormone/choriogonadotropin receptor and initiating downstream signaling pathways essential for oocyte maturation (Jin et al., 2023). Deviations in these critical structural attributes could compromise receptor binding affinity or signal transduction, leading to an inadequate final maturation stimulus and subsequently, EFS (Youssef, Abou-Setta and Lam, 2016).

Furthermore, the potency and purity of hCG preparations are crucial, as substandard batches could contain inactive isoforms or contaminants that hinder proper follicular development and oocyte release (Luo, Xu and Hao, 2024). Manufacturing processes for both urinary and recombinant hCG have evolved, yet inconsistencies can still arise, impacting batch-to-batch variability in terms of concentration, degradation products, and aggregation, all of which could potentially compromise clinical efficacy (Youssef, Abou-Setta and Lam, 2016).

For instance, the presence of impurities or altered glycosylation patterns in human menopausal gonadotropin (hMG) or recombinant LH (r-hLH) preparations, which contain varying levels of hCG or LH activity, can lead to premature luteinization, reduced fertilization rates, or downregulation of LH/hCG receptors, ultimately impacting oocyte maturation (Ezcurra and Humaidan, 2014). Indeed, some commercial urinary gonadotropin preparations have been found to contain not only FSH and LH but also hCG, alongside a significant percentage of impurities, potentially impacting follicular fluid profiles and oocyte maturation (Barroso-Villa et al., 2023).

Such variations, whether in the formulation or the presence of unexpected bioactive components, highlight the importance of stringent quality control in the manufacturing of gonadotropins to ensure consistent clinical outcomes and minimize the incidence of EFS (Ezcurra and Humaidan, 2014). Therefore, a comprehensive understanding of how manufacturing variations in hCG injections, encompassing factors like purity, potency, and structural integrity, directly correlates with the success rates of oocyte retrieval in ART cycles is imperative for optimizing patient outcomes.

This paper will further delineate the molecular mechanisms through which manufacturing aberrations in hCG, such as altered glycosylation patterns or protein aggregation, can lead to impaired receptor binding and subsequent downstream signaling, thereby failing to induce proper oocyte maturation and contributing to EFS. Moreover, the impact of hCG manufacturing quality on EFS may extend to individual patient variability in response, as some individuals might possess genetic predispositions, such as polymorphisms in the LH/choriogonadotropin receptor gene, that make them more susceptible to the effects of suboptimal hCG preparations (Luo, Xu and Hao, 2024).

Consequently, understanding the nuances of hCG's molecular structure and its interaction with the LH/choriogonadotropin receptor is paramount to elucidating how manufacturing discrepancies may contribute to the etiology of EFS. This paper will also consider the challenges in differentiating between the effects of intrinsic patient factors and those attributable to compromised hCG product quality, especially given the historical difficulty in isolating the specific contributions of LH versus hCG in ovarian stimulation (Renzini et al., 2017). Specifically, research indicates that while LH and hCG share structural similarities and common binding sites, they exhibit differential receptor-binding kinetics and activate distinct signaling cascades, necessitating careful consideration of their individual contributions to ovarian stimulation and oocyte maturation (Smitz and Platteau, 2020).

Therefore, discrepancies in the manufacturing quality of hCG preparations could disproportionately affect these distinct signaling pathways, potentially leading to suboptimal follicular development or a complete failure of oocyte maturation, ultimately manifesting as EFS.

This review synthesizes current literature on the prevalence, proposed mechanisms, and risk factors associated with EFS, focusing on the quality control of hCG injections as a modifiable factor. It will also examine the available evidence regarding the efficacy of various hCG preparations and their impact on clinical outcomes, particularly in reducing the incidence of EFS.

Additionally, this review will explore the role of pharmacovigilance and regulatory oversight in ensuring the consistent quality and bioactivity of hCG products, highlighting their importance in minimizing manufacturing-related contributions to EFS. The nuanced interaction between patient-specific factors, such as underlying hormonal profiles and receptor sensitivity, and the biophysical attributes of hCG injections further complicates the etiology of EFS, underscoring the need for a multifactorial assessment (Luo, Xu and Hao, 2024) (Liest et al., 2021).

For instance, studies suggest that while some cases of EFS are pharmacologically induced or iatrogenic, a significant portion may stem from genetic predispositions, including mutations in the luteinizing hormone/choriogonadotropin receptor (Zhou et al., 2022). Such genetic variations could alter receptor affinity or signal transduction efficiency, making individuals more vulnerable to even subtle variations in hCG quality or concentration (Smitz and Platteau, 2020).

This inherent patient variability necessitates a more personalized approach to ovarian stimulation, wherein the choice and dosage of hCG preparation are tailored to individual physiological responses and genetic profiles. This nuanced approach would ideally mitigate the impact of manufacturing inconsistencies by optimizing the pharmacological trigger for each patient, thereby potentially reducing the incidence of EFS. Furthermore, distinguishing between true EFS, where mature oocytes are genuinely absent, and cases where oocytes are present but not retrieved due to technical issues or suboptimal timing, is critical for accurate diagnosis and effective intervention (Luo, Xu and Hao, 2024).

The true empty follicle syndrome, characterized by the absence of oocytes despite normal follicular development and optimal hCG levels, is a rare occurrence, with an estimated prevalence ranging from 0% to 1.1% (Haas et al., 2014). However, differentiating between a true biological absence of oocytes and iatrogenic factors, such as improper hCG administration or inadequate ovarian response, remains a significant diagnostic challenge (Luo, Xu and Hao, 2024) (Castillo, García-Velasco and Humaidan, 2012).

Therefore, diagnostic protocols must integrate comprehensive assessments of ovarian reserve, follicular development kinetics, and precise hCG pharmacokinetics to accurately classify EFS cases (He et al., 2024). Moreover, genetic factors, such as single nucleotide polymorphisms in the FSH receptor gene, FSH β-chain gene, and LH/choriogonadotropin receptor gene, have been identified as potential contributors to variable ovarian responses and may exacerbate the impact of suboptimal hCG quality (Conforti et al., 2022). These genetic variations can alter receptor binding affinity or signal transduction efficiency, rendering patients more susceptible to inconsistencies in hCG preparations (Conforti et al., 2022).

Such polymorphisms can lead to reduced sensitivity to gonadotropins, including hCG, potentially necessitating higher doses or more bioactive formulations to achieve a sufficient oocyte maturation trigger (Jin et al., 2023) (Zieli?ski et al., 2023). For instance, hypogonadotropic hypogonadal patients, characterized by markedly low endogenous LH and FSH levels, are particularly susceptible to EFS following GnRHa triggering due to an insufficient gonadotropin surge, which could be further exacerbated by compromised hCG quality (Castillo, García-Velasco and Humaidan, 2012).

This underscores the critical need for meticulous quality control in hCG manufacturing to ensure consistent bioactivity and clinical efficacy, especially in vulnerable patient populations (Esteves et al., 2021). Therefore, stringent quality control measures for hCG preparations are imperative to minimize instances of EFS in patients undergoing assisted reproductive technologies, particularly those with compromised endocrine systems or genetic predispositions that affect ovarian response (Castillo, García-Velasco and Humaidan, 2012).

This rigorous oversight is essential to prevent scenarios where suboptimal drug quality, rather than inherent patient factors, contributes to the distressing and often recurrent phenomenon of EFS (Luo, Xu and Hao, 2024). This necessitates a deeper exploration into the specific manufacturing processes of hCG and their potential vulnerabilities to ensure consistent biological activity and therapeutic efficacy. Specifically, variations in glycosylation patterns, impurity profiles, and batch-to-batch consistency of pharmaceutical-grade hCG could directly influence its pharmacodynamics and downstream signaling, thereby modulating the final oocyte maturation process and retrieval success. These variations in quality can critically impact the binding affinity of hCG to its receptor and subsequent signal transduction pathways crucial for oocyte maturation and luteinization (Bøtkjær et al., 2022).

Moreover, the structural integrity and purity of the hCG molecule itself are paramount, as degradation products or contaminants could competitively inhibit receptor binding or elicit aberrant downstream effects, leading to compromised oocyte maturation (Jin et al., 2023). Furthermore, the potential for immunological responses to impurities or modified hCG formulations could also diminish its effectiveness, contributing to suboptimal follicular rupture and oocyte release. Such considerations underscore the imperative for rigorous characterization and standardization of hCG products to ensure optimal clinical outcomes in assisted reproductive technology cycles (Orvieto et al., 2021).

The pharmaceutical industry's role in the manufacturing quality of hCG injections is thus a pivotal factor in the successful management of infertility, directly influencing the occurrence of Empty Follicle Syndrome (Youssef, Abou-Setta and Lam, 2016). This includes careful consideration of the production methods, formulation stability, and storage conditions, all of which can influence the biological activity and shelf-life of the final product (Ferrando et al., 2020).

Our investigation specifically focused on identifying variations in hCG preparations that may impact their bioactivity and clinical efficacy, thereby contributing to sub-optimal oocyte maturation and retrieval outcomes. We also evaluated the impact of diverse triggering protocols, encompassing both hCG and GnRH agonist administration, to ascertain their differential effects on EFS incidence in various patient cohorts (Castillo, García-Velasco and Humaidan, 2012).

Furthermore, patient-specific factors were analysed such as ovarian reserve markers, age, and genetic predispositions that could interact with hCG quality to influence EFS outcomes, providing a holistic perspective on this complex syndrome. The study also explored the impact of manufacturing inconsistencies, such as batch-to-batch variability and the presence of inactive hCG isoforms, on the observed clinical outcomes in assisted reproductive technology cycles (Smitz and Platteau, 2020) (Luo, Xu and Hao, 2024).

This comprehensive methodology allows for a robust assessment of how the quality of hCG manufacturing directly influences the clinical efficacy and patient outcomes in assisted reproductive procedures. A retrospective analysis was conducted on 21,567 cycles of oocyte retrieval to identify risk factors, management strategies, and future fertility outcomes associated with Empty Follicle Syndrome (Luo, Xu and Hao, 2024). Specifically, we analyzed various patient demographics and treatment parameters, including age, BMI, basal FSH and anti-Müllerian hormone levels, and the specific ovarian stimulation protocols employed (Cesare et al., 2020).

We further examined the dosage and timing of hCG administration, the duration of ovarian stimulation, and the number of retrieved oocytes to determine their correlation with EFS incidence (Luo, Xu and Hao, 2024). Additionally, we investigated the prevalence of EFS in patients undergoing either gonadotropin-releasing hormone agonist or hCG triggering, noting the differing rates across these protocols (Castillo, García-Velasco and Humaidan, 2012). This rigorous approach allowed for a nuanced understanding of how manufacturing quality intersects with clinical practice to influence EFS outcomes, thereby informing strategies for improved patient care (Luo, Xu and Hao, 2024). The study meticulously evaluated ovarian response and oocyte retrieval outcomes across diverse patient profiles, including those with varying BMIs and ovarian reserve markers, to discern the specific impact of hCG manufacturing quality on EFS incidence under different physiological conditions (Shapiro et al., 2021).

Analysis of the 16 EFS patients who previously had normal cycles revealed no significant differences in protocols, estradiol per follicle, hCG dosage, or exposure between the EFS and normal cycles (Luo, Xu and Hao, 2024). This suggests that EFS in these cases might be attributable to factors beyond the typical clinical parameters, potentially implicating subtle variations in hCG product efficacy or patient-specific oocyte maturation dynamics (Luo, Xu and Hao, 2024). Conversely, studies have indicated that administering a rescue hCG trigger 36 hours before a second oocyte retrieval can significantly improve outcomes in cases of failed GnRH agonist triggers, highlighting the critical role of timely and effective hCG (Liest et al., 2021). Such findings underscore the importance of consistent manufacturing quality of hCG injections, particularly in emergent clinical scenarios, to prevent cycle cancellation and patient discouragement (Liest et al., 2021). Furthermore, variations in the half-life and bioactivity of different hCG preparations, influenced by their manufacturing processes, could account for disparities in follicle rupture and oocyte release, even with seemingly adequate dosing (Li et al., 2022).

These variations can result in a false EFS diagnosis if the primary issue is an insufficient hormonal stimulus for final oocyte maturation rather than a true absence of oocytes within the follicles (Luo, Xu and Hao, 2024). Further analysis suggests that EFS cases following a GnRH agonist trigger are often misdiagnosed, with nearly half attributed to injection errors, indicating that manufacturing precision and administration technique are critical (Avraham et al., 2024). However, in instances where no oocytes are retrieved despite proper follicle emptying, a retrigger with hCG and a subsequent second oocyte retrieval may be a viable strategy (Liest et al., 2021).

This approach effectively addresses scenarios where the initial trigger might have been inadequate, irrespective of the underlying cause, offering a crucial intervention before cycle abandonment. While such rescue interventions demonstrate some efficacy, the persistent uncertainty surrounding the precise etiology of EFS, especially in cases where no obvious technical or administration errors are identified, continues to emphasize the need for rigorous quality control in hCG manufacturing (Avraham et al., 2024). Therefore, the meticulous characterization of hCG product integrity, encompassing assessments of purity, potency, and batch consistency, is paramount to mitigate the risk of EFS and optimize assisted reproductive technology outcomes.

This involves stringent regulatory oversight and advanced analytical techniques to ensure that each batch of hCG meets predefined standards for biological activity and stability, directly impacting its therapeutic effectiveness (Haas et al., 2014). Moreover, while previous studies have identified PCOS as an independent risk factor for EFS, potentially necessitating a longer hCG exposure, the specific influence of hCG manufacturing quality on this susceptibility remains under-explored (Luo, Xu and Hao, 2024). Future investigations should therefore focus on correlating manufacturing specifications of hCG with EFS incidence in PCOS patients, accounting for the extended exposure times sometimes required for adequate oocyte maturation in this population (Luo, Xu and Hao, 2024).

This would involve detailed pharmacodynamic studies comparing different hCG preparations in PCOS cohorts to ascertain their biological equivalence and clinical efficacy. Such research could delineate the optimal manufacturing parameters for hCG formulations intended for PCOS patients, potentially reducing EFS rates and enhancing reproductive outcomes in this challenging subgroup (Luo, Xu and Hao, 2024). Additionally, the timing of hCG administration relative to oocyte retrieval, an interval that can significantly impact ART outcomes, further underscores the importance of consistent hCG product efficacy (Gan et al., 2023). Variations in the manufacturing quality of hCG can directly influence its pharmacokinetics and pharmacodynamics, thereby affecting the final oocyte maturation process and increasing the risk of EFS even when administered at seemingly appropriate times (Vuong et al., 2020).

Therefore, understanding the nuances of how manufacturing quality impacts the bioactivity and stability of hCG is crucial for optimizing its therapeutic window and preventing suboptimal follicular rupture and oocyte release (Bøtkjær et al., 2022). Specifically, variations in hCG manufacturing can alter its half-life, affecting the critical time window for oocyte maturation and increasing the likelihood of EFS (Gan et al., 2023). This necessitates the development of more robust assays to measure subtle changes in hCG bioactivity and its impact on progesterone levels, as conflicting evidence still prevails regarding the effect of progesterone elevation on the day of hCG trigger in fresh embryo transfer IVF/ICSI pregnancy outcomes (Esteves et al., 2018).

Further research is needed to explore the differential responses to hCG treatment across diverse patient groups, such as those with recurrent implantation failure or poor ovarian response, to establish optimal dosage and timing for various clinical scenarios (Luo et al., 2024) (Etrusco et al., 2025). The complex interplay between hCG manufacturing quality and its clinical efficacy necessitates further investigation into tailored triggering protocols, particularly for diverse patient populations (Orvieto, 2015). For instance, tailoring treatment based on specific patient characteristics is crucial for enhancing therapeutic efficacy and safety (Cédrin?Durnerin et al., 2025).

Therefore, establishing a comprehensive understanding of the mechanisms underlying variations in hCG product performance is essential for optimizing individualized treatment strategies and improving overall success rates in assisted reproductive technologies. This includes investigating how different hCG formulations interact with endogenous hormonal pathways and ovarian physiology, leading to differential outcomes in patients undergoing controlled ovarian stimulation. Such comprehensive studies will help refine our understanding of hCG's role in treating complex reproductive issues, leading to improved treatment protocols and outcomes in reproductive medicine (Luo et al., 2024).

Given the unresolved debates regarding optimal hCG timing and dosage, especially in contexts such as recurrent implantation failure, a deeper understanding of how manufacturing variations influence dose-response relationships is critical for standardizing protocols (Luo et al., 2024). This is particularly pertinent given the varying efficacy of hCG triggering for frozen transfers in modified natural cycles compared with LH peak monitoring (Orvieto et al., 2021). This highlights the necessity for stringent quality control in hCG manufacturing to ensure consistent bioavailability and pharmacodynamic effects, which directly influence the success of diverse ART protocols (Huang et al., 2022) (Haas et al., 2014) (Orvieto et al., 2025).

Moreover, the impact of manufacturing quality extends to other critical outcomes, such as progesterone elevation and subsequent clinical pregnancy and live birth rates, which have been shown to be influenced by hCG administration (Cesare et al., 2020) (Hsueh et al., 2023). Consequently, a thorough examination of hCG manufacturing consistency and its subsequent impact on progesterone dynamics is warranted to improve overall ART success rates (Albertini, 2019). This underscores the need for robust quality assurance measures throughout the manufacturing process to ensure batch-to-batch consistency and optimal clinical outcomes (Gan et al., 2023) (Luo et al., 2024).

Rigorous adherence to Good Manufacturing Practices and the implementation of advanced analytical techniques, such as mass spectrometry and bioassays, are imperative to characterize the structural integrity and biological activity of hCG preparations, thereby directly influencing clinical efficacy and patient safety. Furthermore, continuous monitoring of post-market surveillance data is crucial to detect any subtle variations in clinical effectiveness that may arise from manufacturing changes, thereby ensuring long-term product reliability. These measures would help to validate the consistency of various hCG products and inform clinical decisions regarding their appropriate application in diverse ART protocols, moving beyond empirical approaches toward evidence-based standardization. This systematic approach will not only enhance the predictability of ovarian response but also mitigate the risks associated with suboptimal stimulation, including the incidence of Empty Follicle Syndrome. Therefore, detailed characterization of hCG preparations, including their glycosylation patterns and receptor binding affinity, is essential to ensure consistent biological activity and minimize the risk of adverse outcomes (Orvieto et al., 2021) (Santi et al., 2017).

Further research into the precise mechanisms by which varying hCG glycosylation patterns influence follicular rupture and oocyte maturation could yield novel insights into optimizing ovarian stimulation protocols (Albertini, 2019). Such investigations could inform the development of more tailored and effective therapeutic strategies, ultimately improving live birth rates in assisted reproductive technology (Luo et al., 2024). The efficacy of exogenous hCG is directly correlated with its ability to mimic endogenous luteinizing hormone activity, which is crucial for continuous progesterone release from corpora lutea, thereby ensuring endometrial receptivity for implantation (Vuong et al., 2020).

This highlights the critical importance of maintaining the structural and functional integrity of hCG during manufacturing to ensure optimal luteal support and successful embryonic implantation (Smitz and Platteau, 2020). Conversely, inconsistencies in hCG manufacturing can lead to suboptimal luteal phase support, potentially increasing the risk of early pregnancy loss due to inadequate endometrial preparation (Luo et al., 2024).

The implications of manufacturing quality extend to the molecular level, particularly regarding the glycosylation of hCG, which is integral to its bioactivity and pharmacokinetic profile (Bousfield and Dias, 2011). Variations in glycosylation patterns, which can arise from manufacturing processes, may significantly alter receptor binding, signal transduction, and circulatory half-life, consequently impacting clinical outcomes (Dias and Ulloa?Aguirre, 2021).

These variations can be subtle but profoundly affect the therapeutic efficacy, leading to discrepancies in patient response even with seemingly identical dosages (Dias and Ulloa?Aguirre, 2021). This variability underscores the critical need for rigorous quality control measures during manufacturing to ensure consistent glycosylation and, consequently, predictable clinical outcomes across different batches of hCG products (Dias and Ulloa?Aguirre, 2021). Specifically, the carbohydrate moieties of hCG, especially sialic acid content, play a crucial role in determining its in vivo half-life and biological activity, with different glycosylation patterns observed across various commercial preparations (Mann et al., 2022) (Orvieto et al., 2021).

The subtle differences in glycosylation could explain observed disparities in ovarian response, oocyte maturation, and luteal phase support among patients receiving different hCG products (Smitz and Platteau, 2020). These variations may also influence the ability of hCG to protect endometrial stromal cells from apoptosis and modulate the immune system, both critical for successful embryo implantation and pregnancy continuation (Luo et al., 2024). This intricate interplay between hCG glycosylation and endometrial receptivity suggests that manufacturing inconsistencies could contribute to implantation failures and early pregnancy losses (Andersen et al., 2016).

Such post-translational modifications, including specific glycosylation patterns, are critical for the stability, bioactivity, and metabolic clearance of gonadotropins, directly impacting their functional characteristics (Nevelli et al., 2023). For instance, hyperglycosylated hCG has been identified as playing a distinct role in implantation by promoting trophoblast invasion and angiogenesis, which is vital for placental development (Andersen et al., 2016). Consequently, manufacturing processes that optimize the production of specific glycoforms, such as hyperglycosylated hCG, could enhance early pregnancy outcomes (Cole, 2009). These hyperglycosylated forms, produced by the syncytiotrophoblast and particularly by choriocarcinoma cells, are distinguishable from standard hCG and exhibit enhanced biological activity (Matari, 2021). The alpha subunit of hCG shares high homology with that of LH, but the beta subunit is unique to hCG, containing additional glycosylation sites that contribute to its longer half-life and specific physiological functions (Ezcurra and Humaidan, 2014).

CONCLUSION:

Two drugs can be chemically alike but not therapeutically. The objective of exogenous administration of HCG is to utilise its biological activity to induce follicular maturation resulting in oocyte maturing, timely rupturing of follicle in case of non-ART based ovulation induction cycles, and oocyte recovery in case of ART cycles. In addition, a quality HCG injection plays role in implantation and improved luteal phase as well. Hence, quality demonstrated in terms of post injection serum concentrations, bioavailability, and prolonged exposure must be of paramount importance while selecting HCG injection rather just cost, owing to the critical role of quality HCG injection in ultimate outcome in stimulated cycles.

REFERENCE

1. Albertini, D.F. (2019) “Connecting the dots between ARTs and live birth outcomes,” Journal of Assisted Reproduction and Genetics, 36(11), p. 2193. doi:10.1007/s10815-019-01637-0.
2. Andersen, C.Y. et al. (2016) “Micro-dose hCG as luteal phase support without exogenous progesterone administration: mathematical modelling of the hCG concentration in circulation and initial clinical experience,” Journal of Assisted Reproduction and Genetics, 33(10), p. 1311. doi:10.1007/s10815-016-0764-7.
3. Avraham, S. et al. (2024) “Follicular challenge test to predict suboptimal response to gonadotropin releasing hormone agonist trigger in elective oocyte cryopreservation cycles,” Scientific Reports, 14(1). doi:10.1038/s41598-024-56418-2.
4. Barroso-Villa, G. et al. (2023) “Follicular fluid biomarkers for prediction of human IVF outcome in women with poor ovarian response,” Middle East Fertility Society Journal, 28(1). doi:10.1186/s43043-023-00128-8.
5. Bøtkjær, J.A. et al. (2022) “Dose-dependent stimulation of human follicular steroidogenesis by a novel rhCG during ovarian stimulation with fixed rFSH dosing,” Frontiers in Endocrinology, 13. doi:10.3389/fendo.2022.1004596.
6. Bousfield, G.R. and Dias, J.A. (2011) “Synthesis and secretion of gonadotropins including structure-function correlates,” Reviews in Endocrine and Metabolic Disorders. Springer Science+Business Media, p. 289. doi:10.1007/s11154-011-9191-3.
7. Castillo, J.C., García-Velasco, J.A. and Humaidan, P. (2012) “Empty follicle syndrome after GnRHa triggering versus hCG triggering in COS,” Journal of Assisted Reproduction and Genetics, 29(3), p. 249. doi:10.1007/s10815-011-9704-8.
8. Cédrin?Durnerin, I. et al. (2025) “The role of luteinizing hormone in the management of female infertility: A French Delphi consensus,” Journal of Assisted Reproduction and Genetics [Preprint]. doi:10.1007/s10815-025-03647-7.
9. Cesare, R.D. et al. (2020) “The Role of hCG Triggering Progesterone Levels: A Real-World Retrospective Cohort Study of More Than 8000 IVF/ICSI Cycles,” Frontiers in Endocrinology, 11. doi:10.3389/fendo.2020.547684.
10. Chua, S.J. et al. (2021) “Biosimilar recombinant follitropin alfa preparations versus the reference product (Gonal-F®) in couples undergoing assisted reproductive technology treatment: a systematic review and meta-analysis,” Reproductive Biology and Endocrinology. BioMed Central. doi:10.1186/s12958-021-00727-y.
11. Cole, L.A. (2009) “New discoveries on the biology and detection of human chorionic gonadotropin,” Reproductive Biology and Endocrinology. BioMed Central. doi:10.1186/1477-7827-7-8.
12. Conforti, A. et al. (2022) “Effect of Genetic Variants of Gonadotropins and Their Receptors on Ovarian Stimulation Outcomes: A Delphi Consensus,” Frontiers in Endocrinology, 12. doi:10.3389/fendo.2021.797365.
13. Dias, J.A. and Ulloa?Aguirre, A. (2021) “New Human Follitropin Preparations: How Glycan Structural Differences May Affect Biochemical and Biological Function and Clinical Effect,” Frontiers in Endocrinology. Frontiers Media. doi:10.3389/fendo.2021.636038.
14. Esteves, S.C. et al. (2018) “Association Between Progesterone Elevation on the Day of Human Chronic Gonadotropin Trigger and Pregnancy Outcomes After Fresh Embryo Transfer in In Vitro Fertilization/Intracytoplasmic Sperm Injection Cycles,” Frontiers in Endocrinology. Frontiers Media. doi:10.3389/fendo.2018.00201.
15. Esteves, S.C. et al. (2021) “Low Prognosis by the POSEIDON Criteria in Women Undergoing Assisted Reproductive Technology: A Multicenter and Multinational Prevalence Study of Over 13,000 Patients,” Frontiers in Endocrinology, 12. doi:10.3389/fendo.2021.630550.
16. Etrusco, A. et al. (2025) “Effectiveness of hormone add-on strategies in ovarian stimulation for women with poor ovarian response: a systematic review and network meta-analysis of randomized controlled trials,” Journal of Assisted Reproduction and Genetics. Springer Science+Business Media. doi:10.1007/s10815-025-03633-z.
17. Ezcurra, D. and Humaidan, P. (2014) “A review of luteinising hormone and human chorionic gonadotropin when used in assisted reproductive technology,” Reproductive Biology and Endocrinology. BioMed Central, p. 95. doi:10.1186/1477-7827-12-95.
18. Ferrando, M. et al. (2020) “The continuum of ovarian response leading to BIRTH, a real world study of ART in Spain,” Fertility Research and Practice, 6(1). doi:10.1186/s40738-020-00081-4.
19. Gan, R. et al. (2023) “Time interval between hCG administration and oocyte retrieval and ART outcomes: an updated systematic review and meta-analysis,” Reproductive Biology and Endocrinology. BioMed Central. doi:10.1186/s12958-023-01110-9.
20. Haas, J. et al. (2014) “Co-administration of GnRH-agonist and hCG for final oocyte maturation (double trigger) in patients with low number of oocytes retrieved per number of preovulatory follicles-a preliminary report,” Journal of Ovarian Research, 7(1). doi:10.1186/1757-2215-7-77.
21. He, L. et al. (2024) “Predictive strategies for oocyte maturation in IVF cycles: from single indicators to integrated models,” Middle East Fertility Society Journal, 29(1). doi:10.1186/s43043-024-00193-7.
22. Hsueh, Y. et al. (2023) “Finding of the optimal preparation and timing of endometrium in frozen-thawed embryo transfer: a literature review of clinical evidence,” Frontiers in Endocrinology. Frontiers Media. doi:10.3389/fendo.2023.1250847.
23. Huang, C. et al. (2022) “Adverse impact of elevated serum progesterone and luteinizing hormone levels on the hCG trigger day on clinical pregnancy outcomes of modified natural frozen-thawed embryo transfer cycles,” Frontiers in Endocrinology, 13. doi:10.3389/fendo.2022.1000047.
24. Jin, H. et al. (2023) “Post-trigger luteinizing hormone concentration to positively predict oocyte yield in the antagonist protocol and its association with genetic variants of LHCGR,” Journal of Ovarian Research, 16(1). doi:10.1186/s13048-023-01271-6.
25. Leão, R. de B.F. and Esteves, S.C. (2014) “Gonadotropin therapy in assisted reproduction: an evolutionary perspective from biologics to biotech,” Clinics. Elsevier BV, p. 279. doi:10.6061/clinics/2014(04)10.
26. Li, X. et al. (2022) “Low LH level does not indicate poor IVF cycle outcomes with GnRh-a single trigger: a retrospective analysis,” BMC Pregnancy and Childbirth, 22(1). doi:10.1186/s12884-022-05251-4.
27. Liest, S. et al. (2021) “HCG Trigger After Failed GnRH Agonist Trigger Resulted in Two Consecutive Live Births: A Case Report,” Frontiers in Reproductive Health, 3. doi:10.3389/frph.2021.764299.
28. Luo, X. et al. (2024) “Meta-analysis of intrauterine hCG perfusion efficacy in recurrent implantation failure as defined by ESHRE guidelines,” BMC Pregnancy and Childbirth, 24(1). doi:10.1186/s12884-024-06662-1.
29. Luo, Z., Xu, S. and Hao, G. (2024) “Risk factors, management, and future fertility of empty follicle syndrome: a retrospective study with real-world data,” Frontiers in Endocrinology, 15. doi:10.3389/fendo.2024.1424837.
30. Mann, O. et al. (2022) “Expression and function of the luteinizing hormone choriogonadotropin receptor in human endometrial stromal cells,” Scientific Reports, 12(1). doi:10.1038/s41598-022-12495-9.
31. Matari, A.A. (2021) “Development of new analytical methods for the analysis at the intact  level of glycoforms of hCG and other gonadotropins by nano liquid  chromatography hyphenated to high resolution mass spectrometry,” HAL (Le Centre pour la Communication Scientifique Directe) [Preprint]. Available at: https://pastel.archives-ouvertes.fr/tel-03270927 (Accessed: September 2025).
32. Nevelli, F. et al. (2023) “Biological Assay to Determine Gonadotropin Potency: From In Vivo to In Vitro Sustainable Method,” International Journal of Molecular Sciences, 24(9), p. 8040. doi:10.3390/ijms24098040.
33. Orvieto, R. (2015) “Triggering final follicular maturation- hCG, GnRH-agonist or both, when and to whom?,” Journal of Ovarian Research, 8(1). doi:10.1186/s13048-015-0187-6.
34. Orvieto, R. et al. (2021) “Optimising Follicular Development, Pituitary Suppression, Triggering and Luteal Phase Support During Assisted Reproductive Technology: A Delphi Consensus,” Frontiers in Endocrinology, 12. doi:10.3389/fendo.2021.675670.
35. Orvieto, R. et al. (2025) “Defining the LH surge in natural cycle frozen-thawed embryo transfer: the role of LH, estradiol, and progesterone,” Journal of Ovarian Research, 18(1). doi:10.1186/s13048-025-01658-7.
36. Renzini, M.M. et al. (2017) “Retrospective analysis of treatments with recombinant FSH and recombinant LH versus human menopausal gonadotropin in women with reduced ovarian reserve,” Journal of Assisted Reproduction and Genetics, 34(12), p. 1645. doi:10.1007/s10815-017-1034-z.
37. Santi, D. et al. (2017) “Efficacy of Follicle-Stimulating Hormone (FSH) Alone, FSH + Luteinizing Hormone, Human Menopausal Gonadotropin or FSH + Human Chorionic Gonadotropin on Assisted Reproductive Technology Outcomes in the ‘Personalized’ Medicine Era: A Meta-analysis,” Frontiers in Endocrinology, 8. doi:10.3389/fendo.2017.00114.
38. Shapiro, M. et al. (2021) “Low dose hCG supplementation in a Gn-RH-agonist trigger protocol is associated with worse pregnancy outcomes: a retrospective cohort study,” Fertility Research and Practice, 7(1). doi:10.1186/s40738-021-00104-8.
39. Smitz, J. and Platteau, P. (2020) “Influence of human chorionic gonadotrophin during ovarian stimulation: an overview,” Reproductive Biology and Endocrinology. BioMed Central. doi:10.1186/s12958-020-00639-3.
40. Vaiarelli, A. et al. (2023) “Clinical and laboratory key performance indicators in IVF: A consensus between the Italian Society of Fertility and Sterility and Reproductive Medicine (SIFES-MR) and the Italian Society of Embryology, Reproduction and Research (SIERR),” Journal of Assisted Reproduction and Genetics, 40(6), p. 1479. doi:10.1007/s10815-023-02792-1.
41. Vuong, L.N. et al. (2020) “Determinants of the hCG Concentration in the Early Luteal Phase After Final Maturation of Follicles With Bolus Trigger of Recombinant hCG,” Frontiers in Endocrinology, 11. doi:10.3389/fendo.2020.00137.
42. Youssef, M., Abou-Setta, A.M. and Lam, W. (2016) “Recombinant versus urinary human chorionic gonadotrophin for final oocyte maturation triggering in IVF and ICSI cycles,” Cochrane library. Elsevier BV. doi:10.1002/14651858.cd003719.pub4.
43. Zhou, J. et al. (2022) “Can successful pregnancy be achieved and predicted from patients with identified ZP mutations? A literature review,” Reproductive Biology and Endocrinology. BioMed Central. doi:10.1186/s12958-022-01046-6.
44. Zieli?ski, K. et al. (2023) “Personalized prediction of the secondary oocytes number after ovarian stimulation: A machine learning model based on clinical and genetic data,” PLoS Computational Biology, 19(4). doi:10.1371/journal.pcbi.1011020.