Impact of low versus high oxygen tension on human oocyte maturation during biphasic capacitation IVM (CAPA-IVM).

PURPOSE: This study investigated the impact of low versus high oxygen tension on the oocyte maturation rate in biphasic CAPA-IVM. METHODS: A sibling oocyte pilot study of cumulus-oocyte complexes (COCs) from participants with polycystic ovary syndrome was performed at an academic IVF center in Vietnam from November 2023 to May 2024. At collection, COCs were allocated to undergo CAPA-IVM culture with low oxygen tension (5%) or high oxygen tension (20%). Culture of COCs took place in two benchtop incubators, each equipped with commercial mix-gas bottles to establish the respective oxygen conditions. The primary outcome was the oocyte maturation rate. Secondary outcomes were rates of two-pronuclei fertilization, day-3 embryos, blastocyst formation, and good-quality embryos. RESULTS: A total of 554 COCs from 20 participants were assigned to the low oxygen (276 COCs) or high oxygen (278 COCs) tension groups. The oocyte maturation rate was significantly lower in the low oxygen tension versus high oxygen tension group (53.6% vs. 65.8%, risk ratio 0.81, 95% confidence interval 0.71-0.94; p=0.004). The two-pronuclei fertilization rate was significantly lower in the low oxygen tension versus high oxygen tension group (61.5% vs. 72.7%, p=0.03). Numbers of day-3 embryos, blastocysts, and good-quality blastocysts were slightly, but not significantly, lower in the low oxygen tension group compared with the high oxygen tension group. CONCLUSIONS: Low oxygen tension of 5% during both steps of biphasic CAPA-IVM reduced the number of matured oocytes and 2-pronuclei fertilized oocytes compared with the use of high oxygen tension (20%) during CAPA-IVM.