Comparison of HCG Trigger versus Dual Trigger in Improving Pregnancy Outcomes in Patients with Different Ovarian Responses: A Retrospective Study

Objective During in vitro fertilization-embryo transfer (IVF-ET) treatment, the reproductive endocrine regulatory mechanisms hold pivotal importance. Specifically, the serum estradiol (E2) level during ovulation emerges as a critical factor influencing pregnancy outcomes. This retrospective study aimed to comprehensively compare two common clinical regimens based on the grouping of serum E2 levels and the number of oocytes retrieved on the trigger day. Our objective was to evaluate the pregnancy outcomes in IVF-ET patients across different ovarian response groups, exploring the efficacy of the dual-trigger and single-trigger regimens to provide valuable insights for optimizing clinical strategies in the context of IVF-ET. Methods A retrospective analysis was conducted on the clinical data of 2778 infertile patients who underwent ART (IVF/ICSI). Subsequently, a detailed statistical analysis was performed on 1032 patients following an antagonist regimen. Participants were categorized into single-trigger and dual-trigger groups based on real-world trigger protocols, considering different ovarian responses. Comprehensive statistical assessments were conducted on baseline characteristics, ovulation induction, and pregnancy outcomes. Results Baseline characteristics and cycle parameters among the three patient groups (high ovarian response, normal response, and poor response) exhibited no significant differences between the dual-trigger and single-trigger regimen groups. Despite the dual-trigger regimen utilizing a significantly lower HCG dose, no notable discrepancies were observed in laboratory results and pregnancy outcomes (embryo transfer rate, pregnancy rate, and live birth rate) for normal and high responders. Remarkably, E2 levels were higher in the dual-trigger group compared to the single-trigger group. In high and normal responders, the dual-trigger regimen demonstrated increased oocyte counts and oocyte acquisition rates, coupled with decreased transfer cancellation rates attributed to ovarian hyperstimulation syndrome (OHSS). Intriguingly, patients with a poor ovarian response experienced no graft cancellations due to OHSS prevention in either group. Conclusion For patients with high and normal ovarian responses, the utilization of a dual-trigger regimen on the trigger day effectively mitigates the risk of OHSS. Our large sample study supports the substitutability of the dual-trigger regimen over the single-trigger regimen without compromising pregnancy outcomes. However, this conclusion is not applicable to patients with poor ovarian responses. The results of this study highlight the necessity of adopting a customized and individualized treatment approach that should be based on the patient's ovarian response. Additionally, recognizing the pivotal role of the endocrine environment in influencing pregnancy outcomes and the occurrence of OHSS, further exploration of the effects of different triggering regimens on endocrine parameters is warranted. Such investigations will contribute to enhancing the reproductive outcomes of IVF-ET technology.


Introduction
Infertility afects approximately 48 million couples and 186 million individuals globally, underscoring the signifcance of assisted reproductive technology (ART) as a pivotal treatment modality [1].Controlled ovarian hyperstimulation (COH) plays a crucial role in ART procedures such as in vitro fertilization and embryo transfer (IVF-ET) and intracytoplasmic sperm injection (ICSI), aiming to achieve a higher yield of oocytes.
Ovulation is intricately linked to the integrity of the hypothalamic-pituitary-gonadal (HPG) axis, and ovulation triggering stands out as a pivotal step in COH.Typically, human chorionic gonadotropin (HCG) and gonadotropinreleasing hormone agonist (GnRHa) serve as triggers, closely mimicking physiological luteinizing hormone (LH) peaks and inducing ovulation approximately 36-40 hours later.However, the extended half-life and increased receptor affnity of HCG over LH elevate the risk of OHSS, an iatrogenic complication [2].OHSS often occurs in the luteal phase after ovulation induction or early pregnancy, potentially causing respiratory distress and gastrointestinal issues and endangering the lives of patients in severe cases.To mitigate OHSS risk, GnRHa is increasingly favored as a trigger, as it induces endogenous LH peaks more closely resembling natural hormonal patterns [3].Studies indicate that GnRHa triggers can reduce vascular endothelial growth factor mRNA expression, subsequently lowering OHSS incidence [4].For patients with a high ovarian response and the associated risk of OHSS, selecting GnRHa as the trigger has demonstrated efcacy in OHSS prevention.In antagonist cycles, GnRHa triggers are preferred due to heightened pituitary sensitivity.
Te GnRH antagonist protocol, gaining widespread application, proves efective for patients with varying ovarian responses, ofering positive clinical outcomes [5].Despite concerns about reduced corpus luteum function and fresh-cycle embryo transfer rates, frozen embryo transfer presents a viable alternative.Approximately 5.2% of infertility patients exhibit insensitivity to single GnRHa triggers, often observed in those at high risk of OHSS [6].
Te emergence of the dual-trigger regimen, combining HCG and GnRHa, represents a recent development with limited real-world clinical data.Selection of the trigger protocol is guided by serum estradiol (E 2 ) levels, follicle count, patient parameters (height and weight), and previous ovulation responses.In high-response populations, where follicle counts exceed 20 or oocytes obtained surpass 15, the dual trigger is increasingly recommended [7].Compared to the GnRHa single trigger, the dual trigger elevates endogenous LH and FSH levels, enhances oocyte maturity, and increases retrieval rates without compromising success rates.Notably, dual triggering reduces OHSS risk and enhances pregnancy outcomes compared to HCG single triggering [8].
Tis study reviews the clinical data of trigger protocols in patients with diferent ovarian responses to the antagonist protocol, using propensity score matching (PSM) to control for confounding factors and evaluating the efcacy and safety of the dual trigger, combining GnRHa with low-dose HCG.Te observed pregnancy outcomes provide valuable evidence for optimizing clinical strategies in diverse responder populations.Te impact of dual triggers on pregnancy outcomes in diferent response populations.

Materials and Methods
2.1.Study Subjects.Tis observational retrospective study was conducted in a single regional hospital in China, and approval was obtained from the Ethics Committee of Reproductive Hospital Afliated to Shandong University on October 24, 2022.Te ethical approval number is 2022103.Te data extraction was performed in the hospital HIS system.Tis study retrospectively analyzed 2778 infertile women who underwent in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) fertility treatment from January 1, 2018, to December 31, 2020, at the Center for Reproductive Medicine of Shandong University.All enrolled patients signed an informed consent form to allow data collection for research purposes without violating patient privacy or ethical norms.Te quality of sperm is qualifed by routine semen examination [9].

Statistical Analyses.
PSM is a statistical method used to process data.In observational studies, due to various reasons, there are more biases and confounding variables in the data.Te PSM is precisely designed to reduce the impact of these biases and confounding variables in order to make a more reasonable comparison between the experimental group and the control group.In assisted reproduction, the patient's baseline conditions, ovarian response, and triggerday ovarian indicators can all afect pregnancy outcomes.Terefore, whether to use a dual trigger as the dependent variable or exposure factors (patient baseline characteristics, ovarian function, stimulus indicators, etc.) that afect pregnancy outcomes as independent variables, a binary logit model is constructed for 1 : 1 nonreplacement nearest neighbor matching (NNM) of PSM.Using SPSS 23.0, the continuity variable is frst normalized, and the large sample (n > 50) is tested using the Kolmogorov-Smirnov test.Te indicators that meet the normality test are analyzed by the Student's t-test, and the measurement data are presented as mean ± standard deviation (X ± S).Te indicators that did not meet the normality test use the Mann-Whitney U-test when classifed into two groups and the Kruskal-Wallis test when more than two groups are presented by the median M and quartile spacing (P25 and P75).For intergroup comparison of categorical variables, the sample size n ≥ 40 and the theoretical frequency T ≥ 5 use Pearson's chi-squared test, n ≥ 40 and 1 ≤ T < 5 use the likelihood-ratio test, and n < 40 and T < 1 use the Fisher chi-square test, presented as frequencies and percentages.P < 0.05 was statistically signifcant for the diference.

Results
A total of 2540 patients met the inclusion criteria.Tere were matching confounding factors (age, BMI, infertility type, causes of infertility, baseline FSH, baseline LH, baseline E 2 , AMH, total dose of Gn, duration of stimulation, number of large follicles above 14 mm in diameter on the trigger day, serum LH on the trigger day, serum E 2 on the trigger day, serum P on the trigger day, and endometrial thickness on the trigger day) between high responders and normal responders.Te fnal analysis consisted of a total of 1032 patients, including 510 high responders, 388 normal responders, and 134 poor responders (Figure 1).Te three groups before and after matching were compared in terms of baseline characteristics, ovarian stimulation characteristics, and pregnancy outcomes in two trigger groups.
Table 1 shows a comparison of the characteristics of patients in the dual trigger group and the HCG alone group before and after matching against patients at baseline (age, BMI, infertility type, causes of infertility, FSH, LH, E 2 , AMH, and AFC).Te results showed statistically signifcant differences before the propensity score matched the two triggering regimens before matching with the infertility type and AFC in high responders and age, FSH, LH, and AFC in normal responders (p < 0.01).However, there were no signifcant diferences in baseline and cycle stimulation data between the diferent responding populations applying the two triggering regimens after the propensity score matched (P > 0.05).
Table 2 shows statistically signifcant diferences in serum E 2 , HCG dose, and the number of large follicles in the three responding patient populations with the dual trigger regimen (P < 0.01), and no statistically signifcant diferences were found in the rest of the indices.After the propensity score was matched between the populations of the two regimens, there were signifcant diferences in the two trigger groups and HCG doses with p value ≤0.001 in International Journal of Endocrinology diferent responders, and the rest of the results were not statistically diferent.However, most laboratory results in the three ovarian response groups showed slightly higher values in the dual trigger group than in the HCG alone group, proving that there is still an advantage in the dual trigger group.
In the retrieval of patient data, the usual dose of HCG for the single-trigger group is 6000IU, 8000IU, or 10000IU; the usual dose of HCG for the dual-trigger group is 2000IU or 4000IU, and the specifc dosage needs to be adjusted according to the patient's laboratory indicators.We can fnd that in order to prevent adverse reactions to HCG, the dosage of HCG has been reduced for the high responders.
Table 3 shows a comparison of patient characteristics in pregnancy outcomes after matching in the dual trigger group and HCG alone group.Tere were no signifcant diferences in pregnancy outcomes in the diferent trigger groups of normal and high responders as displayed in the results (P > 0.05).Moreover, although there was no statistically signifcant diference between the two triggering regimens in high responders, the incidence of OHSS was lower with dual triggering (3.92 vs. 1.96%).In poor responders, the embryo transfer rate of the HCG-alone trigger group is signifcantly higher than that of the dual trigger group, and there are no cases of transfer cancellation for OHSS prevention in both groups.

Discussion
E 2 is a hormone secreted by ovarian follicular cells that plays an important role in maintaining the growth and development of oocytes.Previous studies have shown an increased risk of OHSS in patients with E 2 > 3500 pg/ml [11].
A very high E 2 level and too many oocytes retrieved increase the incidence of moderate-to-severe OHSS [12].Terefore, the risk of OHSS can be predicted clinically by assessing the trigger-day E 2 level and the number of oocytes retrieved.In this study, the E 2 level of the dual trigger group was higher than that of the single trigger group in the high-response patients and the normal-response patients.
OHSS remains a prevalent complication of COH during ART.Reducing the dose of gonadotropins is the most effective way to prevent OHSS.Recently, the use of Myo-Inositol oral supplementation during ovarian stimulation has been found to reduce the amount of gonadotropins and the time of ovarian stimulation [13].Te combination of GnRHa with an HCG dual trigger can also reduce the dose of HCG, which has shown promising results in preventing OHSS, as previously demonstrated; however, its defnitive role necessitates further substantiation [14].Te theoretical underpinning for the dual trigger, encompassing GnRHa and HCG, lies in its potential to maintain stable luteal function and enhance pregnancy outcomes.Previous research studies, including those conducted by S ¸ükür and Albeitawi, support the superiority of the dual trigger in normal responders [2,15].Chung et al. endorse the dual trigger protocol as an efective strategy for in vitro fertilization in high responders without compromising fresh cycle pregnancy outcomes [16].Li et al.'s study highlights the dual trigger's capability to prevent severe OHSS while maintaining an excellent high-quality embryo rate in highovarian responders following GnRH antagonist protocols [17].Our current study aligns with these fndings, revealing a lower transplant cancellation rate in both high and normal responders within the dual trigger group compared to the single trigger group, attesting to the risk reduction in OHSS   International Journal of Endocrinology occurrence.Importantly, there were no signifcant diferences observed in pregnancy outcomes for high and normal responders, further reinforcing the efectiveness and safety of the GnRHa combined with the low-dose HCG dual trigger protocol when compared to the HCG alone trigger.Contrary to these positive outcomes, Eser A posits that the dual trigger may not yield improved oocyte maturation, clinical pregnancy, or ongoing pregnancy rates in poor responders [18].Our fndings in poor responders corroborate this perspective, with a lower embryo transfer rate observed in the dual trigger group compared to the alone trigger group, signifying potential limitations in its application for this population.
Analyzing the reasons for transplant cycle cancellation, our study underscores the predominant role of OHSS prevention as the primary factor.Te absence of a standardized HCG dosage for the dual trigger in clinical practice, often tailored to individual patient conditions and physician experience, may contribute to the observed high transplant cancellation rate [19].Tis prompts a critical need for further investigation into optimizing HCG dosage to potentially increase the proportion of fresh embryo transfers without elevating the OHSS risk.
Despite our eforts to match baseline patient characteristics and the positive outcomes observed with the dual trigger, this retrospective analysis has limitations.Te inherent biases in clinical preferences for trigger protocols, the smaller population of poor responders, and potential sample loss in matching control baselines are acknowledged.Consequently, defciencies in embryo transfer rates, biochemical pregnancy rates, clinical pregnancy rates, and other parameters warrant consideration.Larger prospective randomized controlled trials are imperative to comprehensively evaluate whether the dual trigger genuinely improves pregnancy outcomes across diverse ovarian response populations and attains superior clinical results.

Conclusions
Our fndings highlight that in patients with high-and normal-ovarian responses, the utilization of a dual-trigger regimen on the trigger day could mitigate the risk of OHSS.Our large sample study validates the substitutability of the dual-trigger regimen over the single-trigger regimen without compromising pregnancy outcomes, and this strategic approach signifcantly mitigates the risk of canceling fresh embryo transfers attributed to OHSS prevention while concurrently yielding favorable pregnancy outcomes.However, this conclusion is not applicable to patients with poor ovarian responses.Te results of this study highlight the necessity of adopting a customized and individualized treatment approach that should be based on the patient's ovarian response.Te expansion of our study's sample size reinforces the robustness of the evidence supporting the dual trigger as a relatively efective and safe regimen.Additionally, recognizing the pivotal role of the endocrine environment in infuencing pregnancy outcomes and the occurrence of OHSS, further exploration of the efects of diferent triggering regimens on endocrine parameters is warranted.Such investigations will contribute to enhancing the reproductive outcomes of IVF-ET technology.

Ovarian Stimulation. All patients are treated with the GnRH antagonist protocol for controlled ovulation induction therapy. Gn is applied to
the dual trigger group with GnRHa and HCG in highresponse patients who have OHSS risk, and those without risk use a single trigger with HCG.2.4.OutcomeVariables (1) Characteristics of patients at baseline: age, BMI, infertility type, causes of infertility, baseline follicle stimulating hormone (FSH), baseline LH, baseline estradiol (E 2 ), antimullerian hormone (AMH), baseline AFC.(2) Characteristics of ovarian stimulation: total dose of Gn, duration of stimulation, number of large follicles above 14 mm in diameter on the trigger day, serum LH on the trigger day, serum E 2 on the trigger day, serum P on the trigger day, endometrial thickness on the trigger day, the dose of HCG, the number of oocytes, the oocyte retrieval rate, the number of fertilizations, the fertilization rate, the number of high-quality embryos, and the high-quality embryo rate.(3) Pregnancy outcome indicators: the embryo transfer rate, clinical pregnancy rate, biochemical pregnancy rate, live birth rate, ectopic pregnancy rate, abortion rate, transplant cancellation rate (reasons: prevention of OHSS, high P value, endometrial factor, embryonic factor, oocyte factor, and others), and OHSS incidence rate.

Table 1 :
Infertile women who underwent IVF/ICSI from January 1, 2018 to December 31, 2020 at the Center for Reproductive Infertile women who underwent IVF/ICSI from January 1, 2018 to December 31, 2020 at the Center for Reproductive Medicine of Shandong University (n=2778) Comparison between the dual trigger group and the HCG alone group before and after matching: characteristics of patients at baseline.

Table 2 :
Comparison between the dual trigger group and the HCG alone group before and after matching: characteristics of patients at stimulation and laboratory results.

Table 3 :
Comparison between the dual trigger group and the HCG alone group after matching: characteristics of patients at pregnancy outcomes.