With an increasing number of women delaying childbirth, POR has become a great obstacle in ART, which could lead couples to abandon treatment or seek oocyte donation19. In clinical practice, GH is commonly utilized as an adjuvant therapy for PORs. However, there are no standardized protocols for the use of GH. Thus, we endeavor to identify the most effective protocol for enhancing the clinical outcomes of POR patients. This study represents a comprehensive synthesis of data regarding currently GH supplementation protocols for PORs undergoing ART therapy. The results of this NMA can be summarized as follows. First, administering 4-8IU/d of GH during the follicular phase of the stimulation cycle was the most commonly used protocol in the clinic and it resulted in the best comprehensive improvement in clinical outcomes for POR patients, including increasing the number of retrieved oocytes, the number of mature oocytes, endometrial thickness on hCG day, and reducing total Gn requirements, but had no effect on the number of fertilized embryos, serum E2 levels on hCG day, live birth rate per embryo transfer cycle. Second, subgroup analysis focus on the clinical pregnancy rate showed that the aforementioned treatment protocol could significantly improve the clinical pregnancy rate of POR patients in the RCT subgroup and the African subgroup, but diagnostic criteria and ovarian stimulation protocols appear to not correlate with the efficacy of this protocol. Third, the long-term treatment protocols have certain advantages in improving the number of retrieved oocytes and endometrial thickness on hCG day, but they are not obvious, so further research remains to be conducted.
Only a handful of prior meta-analyses examined the differences in efficacy among different GH administration protocols on assisted reproductive outcomes in POR patients. Based on the timing of GH administration, Yu et al.20 categorized GH protocols into luteal phase protocols and follicular phase protocols, and the results demonstrated that only GH administration during the follicular phase improved pregnancy rates and live birth rates in patients with POR. Similarly, Cozzolino et al.49 analyzed the influence of GH administration timing on clinical pregnancy rate of PORs and found that positive result was observed only when it was used during the ovarian stimulation period. However, neither of the above studies took into account the dosage of GH. Shang and colleagues18 also confirmed a dose- and time-dependent association between GH and clinical outcomes in POR patients. They indicated that daily administration of < 5 IU/d of GH or administration starting from the follicular phase of the previous cycle before COH increased endometrial thickness and the likelihood of conception more significantly. In contrast, administration of 5–10 IU/day was associated with better oocyte and embryo quality. However, in this report, they only used traditional meta-analysis methods and treated daily dosage and administration timing of GH as two independent variables, which were not conducive to determining the optimal GH administration protocol.
In response to the aforementioned issues, we placed a significant emphasis on additional research. To our knowledge, this is the first meta-analysis to classify GH supplementation protocols by integrating daily dosage and schedule of administration. In accordance with previous research21,49, our findings demonstrate the efficacy of adding GH during the follicular phase of the stimulation cycle. The present NMA indicates that a dosage of 4–8 IU/day of GH administered during the follicular phase of stimulation cycle is the most widely used protocol in clinical practice and has the best comprehensive therapeutic effects on improving the number of oocytes and endometrial thickness, which were regarded two crucial factors for increasing embryo implantation rates and pregnancy rates in assisted reproduction, and reducing the total dose of Gn for ovarian stimulation, which was considered to be one of the important indicators to evaluate ovarian response. In addition to its clinical efficacy, this method also offers the benefits of a shorter administration time, a more moderate injection dosage, and a more convenient injection process, which can alleviate the inconvenience and pain associated with frequent clinic injections, as well as the financial burden on patients. Thus, this protocol seems to be the optimal protocol and has broad applications and research prospects. However, we did not observe the impact of this protocol on fertilized embryo number and E2 level on the hCG day, which may be related to the inconsistent POR diagnostic criteria of the involved patients and the inclusion of non-RCTs, therefore, the results of those endpoints need further confirmation.
Previous meta-analyses have consistently shown controversial results regarding the effect of adding GH on the clinical pregnancy rate and live birth rate of patients with POR. A traditional meta-analysis by Kolibianakis et al.19 suggested that the addition of GH could improve the probability of clinical pregnancy and live birth in POR patients. Another meta-analysis by Yu et al.20 indicated that the clinical pregnancy rate of POR patients is not associated with the addition of GH. Meta-analysis by Shang et al.18 reported that adding GH can improve clinical pregnancy rates and live births in POR patients. The recent meta-analysis by Cozzolino et al.49 showed that supplementation of GH in POR patients increased the clinical pregnancy rate, but did not affect the ongoing pregnancy rate and live birth rate. Some single studies have also drawn inconsistent conclusions35,46,50. In our NMA, no GH supplementation protocol has been proven effective in improving the clinical pregnancy rate and live birth rate of POR patients according to the overall pooled results. However, it is important to consider that the objective of COH is to recruit a sufficient number of follicles to compensate for the inefficiencies of embryo culture and selection for transfer51, and in assisted reproduction, the number of retrieved oocytes is regarded as a significant prognostic variable with a linear correlation to live birth rates52, so it is possible that, despite the lack of improvement in pregnancy rate and live birth rate within a single transfer cycle, the increased quantity and maturity of oocytes may contribute to a greater likelihood of cumulative pregnancies and live births due to more embryos available for transfer and cryopreservation. We look forward to conducting further research in the future to validate this hypothesis.
Medium dose, follicular phase protocol (Protocol D) is extensively employed and relatively effective, so it was the focus of subgroup analyses. We hypothesized, based on existing research, that diverse diagnostic criteria, ovarian stimulation protocols, geographical regions, and ethnicities may contribute to the heterogeneity. In addition, since non-RCTs were included, subgroups were also categorized according to the study design. The results showed low heterogeneity (I2 < 50%) in most subgroups, indicating that the aforementioned factors are likely the main contributors to heterogeneity. We found that when only analyzing RCTs, Protocol D could significantly increase the clinical pregnancy rate of patients, but the overall pooled results showed the opposite effect, partially confirming the efficacy of this protocol but also indicating the uncertainty of the results, which highlights the importance of conducting high-quality RCTs. This protocol received more positive feedback in studies conducted in Africa, which may be attributed to the fact that all African studies were RCTs published within the past decade. Diagnostic criteria and ovarian stimulation protocols appeared to not correlate with the efficacy of Protocol D, but recent studies have shown that the use of GnRH antagonist protocol is gradually becoming a trend in POR patients, in addition, standardized diagnostic criteria is also critical because it can effectively reduce population heterogeneity and improve the repeatability of results. Owing to the small sample sizes, results of subgroup analysis should be interpreted with caution.
It is commonly accepted that the development and maturation of follicles require approximately 75 days, and the role of GH is found to begin at the initial stage of follicle development53,54. Therefore, to enhance oocyte yield, it seems more appropriate to initiate GH co-treatment before commencing ovarian stimulation, which is consistent with the regularity of follicle growth and maturation. Gleicher and colleagues endorsed this hypothesis and suggested that the administration of GH should at least 6 weeks prior to COH, www.clinicaltrial.gov (NCT02179255)13. In this NMA, we have found that compared to the control group, using GH at a dosage > 8 IU/day for not less than 2 weeks before oocyte retrieval could improve the number of obtained oocytes in POR patients but did not show significant advantages compared to the medium dose, follicular phase protocol (protocol D). Therefore, the application value of this protocol needs further exploration. We have also found that the administration of GH at a dosage of 4-8IU/day for not less than 2 weeks had advantages in improving endometrial thickness on hCG day (an important indicator for assessing endometrial receptivity55), which may provide an alternative treatment option for POR patients who have thin endometrium or poor endometrial receptivity, with the goal of improving the implantation rate. Besides, some existing studies have focused on the efficacy of administrating GH at a dosage less than 4IU/day (especially < 1IU/day), which is considered low-dose, for not less than 2 weeks. Lattes et al.56 and Safdarian et al.43 both reported that administration of GH of 0.3-0.5IU/day from the preceding cycle to hCG day had positive effects on ovarian stimulation and pregnancy outcomes. If this protocol is proven effective, its advantages in reducing GH dosage and lowering medical expenses may position it as a promising treatment regimen in the future. Unfortunately, the current evidence from our NMA do not support the widespread application of the low-dose, long-term protocol in clinical practice, and more research is required to further evaluate its effectiveness and advantages. Nonetheless, as a result of the limited number and small scale of extant clinical studies, the level of existing evidence is not strong, and more well-designed trials will be necessary to determine the application value of these protocols.
Other protocols are utilized on a relatively infrequent basis, and they have not demonstrated any advantages in terms of efficacy or cost-effectiveness, indicating limited clinical viability. However, sample size and study design affect the quality of evidence, so the results need to be interpreted rationally.
This study has some limitations that should be considered. First, despite undertaking subgroup analyses, there was still substantial heterogeneity within some subgroups, which may be associated with differences in outcomes across reproductive medicine centers. Due to the small number of available studies, we did not further conduct a meta-regression analysis. Second, there were very few indicators with local inconsistency in our NMA, which may reduce the level of evidence. Third, similar to most of the previous studies, the cost-effectiveness ratio of various protocols was not evaluated, thus, it was not possible to provide clinical recommendations that were appropriate from a health economics standpoint. Fourth, an evaluation of safety, including adverse reactions during medication, risk of birth defects, long-term health status of both mothers and progenies with the use of GH co-treatment were not conducted due to insufficient pertinent data. Fifth, the study by Choe et al.37 used a growth hormone sustained release agent and we categorized it as a high-dose, long-term protocol. However, the reasonableness of this classification method remains to be further explored.
In the future, it will be necessary to conduct larger-scale multi-arm parallel RCTs with rigorous design using the Bologna criteria or the Poseidon criteria to validate the clinical efficacy, cost-effectiveness, and safety profile of various GH supplementation protocols and to provide additional evidence for clinical decision-making. In addition, it is necessary to further investigate the factors that can predict the clinical effects of GH, so that to standardize the indications for incorporating GH in clinical practice.