In-vitro maturation of human oocytes: before or after vitrification?

PURPOSE: This study aims to determine if in-vitro maturation (IVM) of human immature oocytes should be performed before or after vitrification. METHODS: A total of 184 immature oocytes were randomly divided into two different groups: 100 were vitrified at metaphase II (MII) stage 24 h-48 h after IVM (group 1) and 84 were immediately vitrified at germinal vesicle (GV) or metaphase I (MI) stages and in vitro matured after warming (group 2). RESULTS: Survival rate after warming was similar in both groups (86.9% versus 84.5%). However, oocyte maturation rate per collected oocyte was significantly higher for oocytes matured before vitrification (group 1, 46%) than for oocytes vitrified before IVM (group 2, 23.8%) (p < 0.01). Consequently, the number of MII oocytes inseminated per oocyte collected was significantly higher for group 1 (40%) than for group 2 (23.8%) (p < 0.05). CONCLUSION: IVM procedure is more efficient when it is performed before oocyte vitrification.JOURNAL ARTICLESCOPUS: ar.jinfo:eu-repo/semantics/publishe

Follicle environment and quality of in vitro matured oocytes

In mammalian reproduction, the oocyte depends on the ovarian follicle for most of its growth. They form a bipolar partnership and the status of one will impact the functioning of the other. When oocytes are removed from their follicle by ovulation, they have normally completed all the steps required to begin their journey into the oviduct and drive the early embryonic development. When oocytes are removed from their follicle before natural ovulation, the process by which they acquire all the important components for their journey might not be completed and their ability to mature, fertilize or develop into embryos or to term might be compromised. Animal models have been useful to define the important steps required for the oocyte’s growth phase, and in the mouse, when the oocyte has reached its full size, the program is ready. This is not the case in larger mammals where the completion of growth does not ensure that the oocyte is fully capable of undergoing all the steps to the embryo and to term. The final steps of oocyte preparation also involve a progressive condensation of the chromatin that may facilitate normal maturation but may also indirectly reduce the lifespan of the oocyte. In such a scenario, the oocyte would have an expiration date when fully competent. In humans, a number of indications may justify the aspiration of oocytes from unstimulated patients and the development of an in vitro maturation (IVM) process that would allow fertilization and subsequent development. This objective could be realized by a better understanding of the essential follicular contribution required before removing the oocyte. Therefore, this review will focus on the large animal models where IVM has been used and studied for more than 25 years. The status of the follicle at the time of oocyte recovery and the status of the oocyte’s chromatin will be described in detail as they have a significant impact on the outcome