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

Research Laboratory on Human Reproduction, Medicine Faculty, Université Libre de Bruxelles, Belgium, Campus Erasme, Brussels, Belgium.
Journal of Assisted Reproduction and Genetics (Impact Factor: 1.72). 04/2012; 29(6):507-12. DOI: 10.1007/s10815-012-9751-9
Source: PubMed


This study aims to determine if in-vitro maturation (IVM) of human immature oocytes should be performed before or after vitrification.
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).
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).
IVM procedure is more efficient when it is performed before oocyte vitrification.

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Available from: Giovanna Fasano
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    • "Cryopreservation of immature oocytes is expected to allow greater flexibility in the timing and location of artificial embryo production. Cryopreservation of fully grown but immature oocytes using vitrification rather than conventional freezing has been studied in mice [1], cattle [2,3,4], sheep [5, 6], pigs [7, 8] and humans [9], and offspring have been obtained from mice and cattle [1, 2]. The cohort of growing oocytes in the ovary is a potentially larger source of oocytes compared with those that are fully grown. "
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    ABSTRACT: Cryopreservation of growing oocytes enriches the choice of timing and location of artificial embryo production. However, completion of oocyte growth after warming is crucial when using such cryopreserved oocytes. Our research objective was to develop a sequential system that incorporates cryopreservation of growing bovine oocytes and their subsequent in vitro growth. Oocyte-granulosa cell complexes with a mean oocyte diameter of approximately 100 µm were vitrified-warmed and then cultured for 14 days. The percentage of surviving oocytes following cryopreservation and 14-day culture was approximately 80%. More than half of the surviving oocytes were capable of maturing to metaphase II after in vitro maturation; the rate was comparable to that of control oocytes grown in vitro without cryopreservation. Taken together, the combined protocols for vitrification-warming of growing oocytes and subsequent in vitro growth can produce oocytes capable of undergoing meiotic maturation.
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    • "Finally, the oocytes were rinsed in Ham's F10 and 20% HSA for 3–5 times. After this stage, the oocytes were transferred into IVM medium for 36 h in incubator and checked after 1 h for survival [16]. Post-warming survival rate was assessed using morphological criteria, indicated by the absence of overt cell degeneration, elongated shape, thick or distorted zona, expanded perivitelline space (PVS) and dark cytoplasm. "
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    ABSTRACT: Objective: To describe the possible effects of cryotop vitrification on maturation rate and ultrastructural morphology of human in vitro matured germinal vesicle (GV) oocytes. Study design: A total of 301surplus immature GV oocytes obtained from infertile patients were allocated into two groups: (i) GV oocytes (n=150) matured in vitro (fIVM), and (ii) GV oocytes (n=151) that were first vitrified, then matured in vitro (vIVM). Supernumerary fresh in vivo matured oocytes (n=10) were used as controls. The maturation media was Ham's F10 supplemented with FSH+LH and human follicular fluid. After 36h of incubation, the oocytes were investigated for nuclear maturation and ultrastructural changes using transmission electron microscopy (TEM). Results: Oocyte maturation rates were reduced (P<0.001) in vIVM (45.92%) in comparison with fIVM oocytes (75.33%). The rate of degeneration was also significantly higher in vIVM than in the fIVM group (44.4% vs. 6.0%). Large and numerous mitochondria and minute vesicles of smooth endoplasmic reticulum (SER) complexes (MV complexes) were observed in both fIVM and vIVM groups. In addition, TEM revealed a drastic reduction in amount of cortical granules (CGs) at the cortex of vitrified-warmed GV oocytes, as well as appearance of vacuoles and small mitochondria-SER aggregates in the ooplasm. Conclusion: The vitrification procedure is associated with ultrastructural alterations in specific oocyte microdomains, presumably related to the reduced competence of cryopreserved oocytes for maturation. This information emphasizes the need for further work on advancing the cryotechnology of human oocytes.
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