This retrospective cohort study is the first to assess the effects of dual-trigger on IVF outcomes in patients fulfilling the POSEIDON group 4 criteria. Our study showed that dual-trigger is superior to hCG administration alone for final oocyte maturation in producing increased numbers of retrieved oocytes, metaphase II oocytes, fertilized oocytes, day-3 embryos and top-quality day-3 embryos. Clinical pregnancy rate and live birth rate were also improved with dual-trigger administration. Moreover, the multivariate analysis revealed a 3.58-fold increase in clinical pregnancy (95% CI 1.26–10.17, p = 0.017) and a 4.18-fold increase in live birth (95% CI 1.11–15.83, p = 0.035) in the POSEIDON group 4 patients with dual trigger compared to those with hCG trigger. When the population is further divided into subgroups of < 40 and ≥ 40 year olds, we found a significant improvement across all abovementioned parameters for the patients < 40 years. For the subpopulation ≥ 40 years, a significant increase was seen in number of oocytes retrieved, fertilized oocytes, number of day-3 embryos and top-quality day-3 embryos. Clinical pregnancy rate and live birth rate for this population also trended towards improvement, although not statistically significant.
Similar outcomes have been obtained in the study of patients with diminished ovarian reserve or poor ovarian reserve in recent years, showing a beneficial effect of dual-trigger in improving IVF outcomes. Lin et al. [22] confirmed in a recent retrospective cohort study involving 427 GnRH antagonist IVF cycles with fresh embryo transfer that dual-triggering significantly increases the live birth rate (26.9% vs 14.5%, p = 0.014), clinical pregnancy rate (33.0% vs. 20.7%, p = 0.035), and fertilization rate (73.1% vs. 58.6%, p = 0.015) in women with diminished ovarian reserve, compared to hCG-alone trigger. In an even larger retrospective cohort study with 1389 IVF cycles fulfilling the Bologna criteria, utilizing the progesterone-primed ovarian stimulation protocol, Zhang et al. [23] also reports significantly higher number of oocytes collected (p < 0.001) with improved number of mature oocytes (p < 0.001). However, other studies have found dual-trigger to be ineffective at improving IVF outcomes for this population. Eser et al. [24], in a case control study involving 47 dual-trigger and 62 hCG only trigger cases fulfilling the Bologna criteria for POR, discovered no statistical different between the two groups with reference to implantation rate, biochemical pregnancy rate, clinical pregnancy rate, and ongoing pregnancy rate. Due to the divergence of opinion on the effectiveness and clinical utility of dual-trigger for final oocyte maturation, large scale randomized controlled trials are required to reach a verdict.
In combining GnRH agonist and hCG for the final oocyte trigger, we are in essence enjoying the best of both worlds. Despite being molecularly similar, hCG and LH elicit different gene expressions. LH tends towards cellular growth, which supports embryo development and survival, whereas hCG enhances apoptosis [25,26]. hCG administration alone also does not produce FSH activity, while GnRH agonist releases an endogenous FSH and LH surge, resulting in a more physiologic response. In vitro studies have highlighted the role of FSH in oocyte maturation [3], via the increased production of epiregulin (Ereg) and amphiregulin (Areg) [27], members of the epidermal growth factor-like (EGF) family, which have been shown to mediate the LH signal and participate in cumulus expansion and oocyte maturation [28]. This has been confirmed in vitro experiments, where Ereg and Areg presence in maturation medium helps to improve the maturation rate of human GV oocytes [29]. Animal studies have also shown that FSH has the independent ability of inducing ovulation [30], perhaps by stimulating plasminogen activator activity, which converts plasminogen into active protease plasmin, helping to weaken the follicular wall and aiding rupture and oocyte dissociation [3,31,32]. Also, the FSH surge induces LH formation on luteinized granulosa cells, promoting oocyte maturation and cumulus expansion [33]. Clinically, randomized controlled trials have shown that administration of FSH along with hCG trigger increases the rate of oocyte recovery and improved the fertilization rate (40). In their study, 188 women undergoing a long agonist suppression protocol for treatment of infertility were randomized to receive a FSH bolus versus placebo at time of hCG trigger. Fertilization rates were significantly higher (63% vs. 55%) in the treatment arm, with increased likelihood of oocyte recovery (70% vs. 57%). However, this did not translate into a difference in clinical pregnancy rate or live birth rate.
Additionally, direct GnRH receptor activation as identified by Raga et al. could also have an effect on preimplantation embryonic development that is unrelated to FSH activity [34]. The GnRH receptor expression was found to be greatest in granulosa cells [35], and in rat models, administration of GnRH agonists induced an increase in receptor levels in a dose-dependent manner, whereas LH decreased GnRH receptor mRNA levels [36]. Administration of GnRH agonist trigger has also demonstrated the retrieval of more MII oocytes (16%) [9]. As such, the triggering cocktail of hCG, FSH, LH and GnRH agonist serves to provide the benefits of a multi-faceted approach.
In our study, the patients who stand to benefit the most from such a trigger regimen appear to be those less than 40-years of age. Other possible subgroups include those with low proportion of mature oocytes (< 66%) per number oocytes retrieved [37], where it was demonstrated that patients who received dual-trigger had significantly higher number of MII oocytes (6.5 vs. 3.6, p < 0.008), number of oocytes retrieved (69.7% vs. 47.1%, p < 0.03), and a higher number of top-quality embryos (3.1 vs. 1, p < 0.02) [38]. Moreover, those with history of poor fertilization, as defined by fertilization rate < 20% in at least two prior ICSI cycle, are also a potential benefit of such a combination. In their retrospective cohort study, Elias et al. [39] found in 2017 that the mean fertilization rate in the combined trigger group was found to be significantly higher 16.4% (95% CI: 7.58% - 25.2%), with higher oocyte maturity (82.1% vs. 69.8%), higher clinical pregnancy (27.5% vs. 5.67%), and higher live birth rates (20.2% vs. 3.46%) compared to the hCG trigger group.
The relatively small sample size of this study along with its retrospective design poses major limitations. We are underpowered to analyse if dual-trigger has an impact on IVF outcomes of patients aged less than or more than 40 years old. Another shortcoming of our study is that despite all cycles being antagonist cycles, we only took into account total gonadotropin dosage, and there is considerable heterogeneity in exact type of gonadotropin used. The strength of our study is that all clinical decisions and oocyte pick-ups were performed by the same physician, leading to less variability in performance.
In conclusion, our data suggest that dual trigger might increase both oocyte and embryo yields, as well as clinical pregnancy rates and live birth rates in patients fulfilling the POSEIDON group 4 criteria. However, large-scale randomized controlled studies are needed to confirm these findings.