Abstract
The combination of in vitro maturation (IVM) techniques and oocyte vitrification (OV) could increase the number of useful oocytes in different types of patients. IVM and subsequent OV is the most widely used clinical strategy. Would the results improve if we reverse the order of the techniques? Here, we evaluated survival, in vitro maturation, time to extrude the first polar body (PB), and the metaphase plate configuration of human prophase I (GV) oocytes before or after their vitrification. Specific, 195 GV oocytes from 104 patients subjected to controlled ovarian stimulation cycles were included. We stablished three experimental groups: GV oocytes vitrified and IVM (Group GV-Vit), GV oocytes IVM and vitrified at MII stage (Group MII-Vit), and GV oocytes IVM (Group not-Vit). All of them were in vitro matured for a maximum of 48 h and fixed to study the metaphase plate by confocal microscopy. According to our results, the vitrification of immature oocytes and their subsequent maturation presented similar survival, maturation, and metaphase plate conformation rates, but a significantly higher percentage of normal spindle than the standard strategy. Additionally, the extension of IVM time to 48 h did not seem to negatively affect the oocyte metaphase plate configuration.
Highlights
Oocytes vitrification (OV) protocols developed during the last decade have allowed the introduction of this technique in all assisted reproduction (AR) laboratories
We showed that extending in vitro maturation (IVM) could increase the number of available oocytes without altering their quality, at least regarding the metaphase plate configuration
The use of in vitro matured oocytes in reproductive cycles with or without stimulation, combined with the vitrification technique, involves novel ways of action and allows us to maximize the efficiency of the AR laboratories’ techniques. Their clinical use is conditioned to the collection of competent metaphase II (MII) oocytes, which are able to sustain early embryonic development
Summary
Oocytes vitrification (OV) protocols developed during the last decade have allowed the introduction of this technique in all assisted reproduction (AR) laboratories. This is based on the quick freezing of the oocytes in a medium with high cryoprotectants (CRP). One of the greatest challenges of OV is the disruption of the meiotic spindle [5,6,7,8,9]. The spindle, which is formed mainly by microtubules, is responsible of chromosome segregation [10]. The microtubules are very sensitive to temperature so, oocyte preservation is associated with an increase in embryonic aneuploidies [11,12,13]. It is known that this structure is dynamic and can repolymerize when the physiological conditions are recovered [14,15,16,17,18,19]
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