Controlled ovarian hyperstimulation (COH) is still a big challenge in women with PCOS due to the abnormal endocrine and metabolic environment. The GnRH-ant protocol has been widely accepted as a prominent intervention to reduce the risk of OHSS [13], and been recommended by WHO as a COH choice for PCOS patients [13]. This study was the first one to compare the mGnRH-a ptotocol and the mainstream GnRH-ant protocol from aspects of live birth rate, safety and economic cost. Although this was a retrospective study, the power was greatly improved by using PMS statistical methods to adjust for potential non-similarities between groups. At last, our study showed that the mGnRH-a protocol could achieve a higher live birth rate and there were no significant differences in the incidence of OHSS or the cost of COH process when compared with GnRH-ant protocol.
Prolonged GnRH agonist protocol is mainly utilized for the treatment of endometriosis and has obtained relatively high pregnancy rates [9, 17, 18]. Later, the mGnRH-a protocol with only one injection has emerged in China and is gradually used among infertile patients including non-endometriosis. But the evidence of better clinical outcome from mGnRH-a protocol is limited. In 2014, Ren et al. [11] observed a higher live birth rate (55.56% vs. 45.73%, P = 0.006) in women who had normal ovarian response with the mGnRH-a protocol when compared with the GnRH agonist long protocol. Similarly, this superiority was also found in patients with PCOS who treated with mGnRH-a protocol (60.13% vs. 48.95%, P = 0.025) [10]. Moreover, Fei Gong et al. reported a higher clinical pregnancy rate (77.94% vs. 61.29%, P = 0.039) in patients suffering from PCOS using mGnRH-a protocol than those who used GnRH agonist long protocol and our study further showed a higher live birth (58.22% vs. 41.78%, P = 0.0004). However, mechanisms of the results are currently unclear. Some studies reported endometrial receptivity as the main limitation of gestation for women suffering from PCOS [12], and HOXA10, MEIS1 and LIF mRNA and protein expression in endometrium all showed significantly higher in the mGnRH-a protocol than in the GnRH-ant protocol and GnRH agonist long protocol [19], suggesting a significant priority of mGnRH-a protocol on improving endometrial receptivity for patients with PCOS.
Baseline characteristics
We used the propensity score matching method to control the potential confounders between mGnRH-a group and GnRH-ant group. The PSM method was first described in the 1980s by Rosenbaum and Rubin [20], but it was not widely used by statisticians until the 2000s, especially in medicine. This method is useful for observational studies in which treatment allocation is non-random and can be viewed as an approach seeking to replicate random assignment in conventional randomized controlled trials [21]. The other advantage of the PSM method for this study is that it allows parallel comparisons among the three main outcomes instead of multiple logistic regression for each end point. Before matching, the GnRH-ant group had a longer duration of infertility, more AFC and higher proportion of IVF treatment history and scar uterus. After matching, the difference in those characteristics between groups became very small.
Ovarian stimulation and embryos culture outcomes
In our study, the mGnRH-a protocol had a longer follicular stimulation period, more Gn dosages and lower serum E2, LH and P4 levels on the HCG trigger day than GnRH-ant protocol. One of the possible explanations is that a long-acting GnRH-a injection could deeply suppress the pituitary-ovarian axis. In GnRH-ant protocol, the ovarian stimulation period was short, which might be attributed to the rapid inhibition of the endogenous LH release without pituitary desensitization [7]. In addition, because of a higher E2 level on the HCG trigger day (3224.8 vs. 2590.6), the proportion of frozen embryo transfer in the GnRH-ant group should be higher than that in the mGnRH-a group to take precautions against the occurrence of OHSS.
An increasing number of transferable embryos and cycles with transferable embryos were observed in mGnRH-a group compared with GnRH-ant group. This might benefit from GnRH agonist, which reduced cancellation rate by preventing premature LH surge, and increased the number of oocytes and embryos transferred [22]. Animal studies showed that GnRH agonist increased the proportion of mouse embryos that reached the blastocyst stage in vitro. Casan et al. [24] found the expression of GnRH and its receptor in human preimplantation embryos. Even so, direct evidence supporting the role of GnRH agonist in human embryo remains limited. Moreover, with the increase of the number of transferable embryos, the proportion of blastocyst transfer in mGnRH-a group was higher than that in GnRH-ant group according to our standard of blastocyst culture.
Previous studies [11, 17] observed a thicker endometrium in prolonged GnRH agonist protocol than that in other protocols, which was consistent with our data. Endometrium thickness has been used as a marker of the uterine receptivity to embryos, and as a predictor of IVF-ET success [11, 17]. Although related mechanisms are still unclear, it could be associated with the hypothesis of endometrial recovery. A break of constant menstrual cycling by prolonged down-regulation may restore full function to the steroid-sensitive systems [27].
Clinical outcome and economic indicators
Unlike other studies, we think it is more reasonable to define the live birth rate as live birth per started treatment cycle after first fresh or frozen embryo transfer, instead of live birth per fresh or frozen transfer in our study. Fresh or frozen embryo transfer was chosen according to the patient’s conditions and laboratory tests results. For instance, it is more suitable to conduct frozen embryo transfer for GnRH-ant group with a high E2 level on the HCG trigger day. Therefore, it is not comprehensive to simply compare outcomes of fresh or frozen transfer cycle alone. Cumulative live birth rate (CLBR) was suggested as a suitable way to report success of an IVF treatment [28]. However, follow-up time of two years is too long and difficult to achieve. The live birth per started treatment cycle after first fresh or frozen embryo transfer is an intermediate choice; it does not require all embryos to be transferred, and it can take into the account outcomes of both the fresh transfer and frozen transfer.
Women with PCOS who require IVF treatment are at particular risk of OHSS. A systematic review with 9 RCTs published before 2012 [29] showed PCOS patients with the GnRH-ant treatment had a lower severe OHSS rate (5.52% [35/634] vs. 12.42% [82/660]) than treated with standard GnRH agonist long protocol. In 2016, Chen et al. [29] reported a lower moderate or severe OHSS rate (1.3% [10/746] vs.7.1% [54/762]) in the frozen-embryo group than that in the fresh-embryo group. Therefore, the GnRH-ant protocol combined with freeze-all embryo can minimize the occurrence of OHSS. In our study, the mGnRH-a group had a moderate to severe OHSS rate of 4.28% (25/584) and a severe OHSS rate of 0.17% (1/584), which were relatively higher than the GnRH-ant group (2.05% and 0%, respectively), but the difference was not statistically significant. However, this is a retrospective study and it spans 5 years. The protocol was constantly improved by increasing the intensity of single blastocyst transfer, reducing the initial Gn dose, and expanding the standard of freeze-all embryo. Further optimizations are still needed with the inherent defect of not being able to apply GnRH agonist trigger.
For economic indicators, remarkably, our data significantly favored higher total dosages of exogenous Gn in the mGnRH-a group, but the costs were lower than expected, the reason for which was that patients in the mGnRH-a group received more HMG injections. HMG contains the same dosage of LH and FSH, which may be one of the sources of exogenous LH. Too low serum LH level in COH may affect follicular development, which directly influenced the potentiality of oocyte and embryo. Previous studies have reported that the LH level during ovarian stimulation should neither be too high nor too low [31, 32]. Thus, patients in the mGnRH-a group with low serum LH levels after prolonged pituitary depression usually used HMG instead of rFSH or added recombinant LH when serum LH levels were < 1 IU/L. In addition, the corresponding cost of transvaginal ultrasonography and endocrine hormone tests rose due to the longer period of ovarian stimulation in the mGnRH-a protocol.
Limitations
An apparent defect of this study was that there were only 146 patients in the GnRH-ant group. For the live birth rate outcome, this sample size is enough to detect a statistical significance because of a large effect size. For economic outcomes, the power of independent t-test was acceptable for data following continuous normal distribution with a relatively small standard deviation. However, there were only 3 patients with moderate-to-severe OHSS in the GnRH-ant group. The contingency of this probability suggests that more research with larger sample sizes should be conducted. It is estimated that GnRH-ant protocol would achieve a lower OHSS rate by expanding the sample size.