Smooth endoplasmic reticulum aggregates in oocytes: a comparison of progestin-primed and GnRH antagonist IVF protocols.

Background: Vitrification improves post-thawed embryo recovery and enables new strategies for in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI). Due to its convenience and efficacy, progestin-primed ovarian stimulation (PPOS) gets more attention in daily practice. However, concerns about the impact of PPOS on oocyte and embryo quality still exist. We aimed to compare the embryological and pregnancy outcomes between PPOS and gonadotropin-releasing hormone (GnRH) antagonist protocol in IVF/ICSI cases.

Methods: This was a retrospective cohort study of 545 women undergoing IVF/ICSI cycles from July 2017 to December 2018. The patients were allocated into two groups: the PPOS and GnRH antagonist group, based on 1:1 propensity score matching. In both groups, all viable embryos were cryopreserved for later transfer. The primary endpoint was the prevalence of smooth endoplasmic reticulum aggregates (SERa) in oocytes. Secondary outcomes included the cycle characteristics and pregnancy outcomes.

Results: Ovarian stimulation duration and serum estradiol level on trigger day were significantly higher in the PPOS group compared to the GnRH antagonist group. The prevalence of SERa + cycles was 9.4% in our cohort (13.0% and 12.2% in the PPOS and GnRH antagonist groups, respectively, p = 0.221). There were more frozen embryos (5.3 ± 4.5 vs. 4.8 ± 4.0, p = 0.378) in the PPOS group than in the GnRH group, particularly for the subgroup of low responders (1.6 ± 1.2 vs. 1.2 ± 1.0, p = 0.043). No significant differences were observed between the groups regarding clinical pregnancy rate, miscarriage, live birth rate, and cumulative live birth rate in the following two years after oocyte retrieval.

Conclusions: Our findings suggest that the PPOS protocol provides clinical benefits and safety with comparable oocyte quality and pregnancy outcomes to the GnRH antagonist protocol.