ARTICLE
Auteur(s) : Gloria
Calderón
IVI-Barcelona, Ronda General Mitre 14, 08017 Barcelona,
Espagne
Human oocyte maturation is considered as the reinitiation and
completion of the first meiotic division from the germinal vesicle
stage (prophase I) to metaphase II, and also come along with
cytoplasmic maturation for fertilization and early embryonic
development [1].
The recovery of immature oocytes followed by in vitro maturation
(IVM) and in vitro fertilization is now a days, one more
alternative to conventional in vitro fertilization (IVF). In an IVM
cycle there is no need to use controlled ovarian stimulation
(although recently it has been demonstrated the need of small
amounts of hormones to obtain better results), meaning no risk of
ovarian hyperstimulation syndrome (OHS), reduced cost and is a much
simpler procedure than IVF. Lately, it has been demonstrated that
retrieval of immature oocytes followed by IVM is a successful
treatment for women with polycystic ovary syndrome (PCOS) because
there are many antral follicles in the ovaries, for women with poor
morphology embryos due to low or poor response to high doses of
gonadotrophins and also for PCO patients considering egg donation.
IVM can also be an option for patients willing to preserve their
fertility due to cancer and treated with chemotherapy or
radiotherapy. In general, the clinical pregnancy and implantation
rates after IVM have reached 30-35% and 10-15% [2].
In vitro maturation procedure
It is known that cumulus-oocyte complexes can be spontaneously
induced to resume meiosis when they are released from follicles
into culture conditions in vitro. Therefore, endocrine factors
affecting this process may be different from in vitro conditions.
Oocyte maturation in vitro is profoundly affected by culture
conditions. The beneficial effect of surrounding cumulus cells on
oocyte maturation in vitro and early embryonic development have
been demonstrated in humans. Cumulus cells are considered to play
and important role in oocyte maturation by keeping the oocyte under
meiotic arrest, by participating in the induction of meiotic
resumption and by supporting cytoplasmic maturation. An adequate
cytoplasmic maturation of the oocyte is always required to obtain
better embryo morphology. Moreover, cytoplasmic organelles and
structures are needed to accomplish maturation. A massive increase
in mitochondria, chromatin remodelling, protein and RNA synthesis
etc., is needed to avoid chromosomal non-disjunction producing
embryo aneuploidy.
Nowadays and thanks to the use of recombinant FSH and LH and
inactivated maternal serum [3] in culture medium for IVM a
significantly higher maturation, fertilization, blastocyst
formation, pregnancy an implantation rates have been reported.
Clinical applications
IVM in stimulated or non stimulated cycles can be a useful
treatment for low responders, PCO syndrome and PCO like ovaries.
Also IVM can be used in routine IVF cycles to perform germinal
vesicle rescue. IVM will also be necessary to in vitro culture of
primary follicles of fresh or frozen ovarian tissue.
Some groups have obtained better results using conventional
insemination instead of ICSI.
Conclusion
Lately pregnancy and implantation rates obtained after IVM of
immature oocytes have been improved. Then, as an option, IVM can be
offered to women whose infertility are due to PCOS or ovaries PCO
like, low responders or advanced maternal age. The combination of
natural cycle IVF with retrieval of immature oocytes and IVM it has
become an excellent treatment for women with all types of
infertility that not want to suffer ovarian stimulation. Even
though, extensive research still has to be done to address the
mechanism of oocyte maturation in order to redefine culture
conditions and increase pregnancy and implantation rates.
References
1 Edwards RG. Are minimal stimulation IVF and IVM set to
replace routine IVF ? RBM Online 2007; 14: 267-70.
2 Papanikolaou EG, Platteau P, Albano C,
et al. Inmature oocyte in-vitro maturation: Clinical aspects.
RBM Online 2007; 10: 587-92.
3 Mikkelsen AL, Host E, Blaabjerg J,
Lindenberg S. Maternal serum supplementation in culture medium
benefits maturation of inmature human oocytes. RBM Online 2001; 3:
112-6.
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