الفهرس 
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Abstract
While comparing a pregnant cohort to a non¬pregnant cohort following IVM, Child et al. observed a statistical significance difference between endometrial thicknesses: greater than 10 mm on the day of embryo transfer was a good predictor of pregnancy. Hence, endometrial preparation is necessary and must take place in a very short period of time unless it begins before oocyte retrieval . Starting 17β-estradiol early in the cycle could permit a better endometrial preparation and may improve the cancellation rate. However, the prospective work of Russell suggested that early exposure of ovaries to 17β-estradiol could impair oocyte maturation, fertilization, and cleavage. The global effect will depend on the improvement of the implantation rate induced by 17β-estradiol.
Metformin
This fashionable insulin-sensitizing drug has been recently tried for many aspects of ART, sometimes without any conclusive benefit. Two
observational retrospective studies with metformin alone and one with the addition of enoxaparin suggest that metformin could decrease the miscarriage rate of PCOS when continued at the beginning of the pregnancy. On the other hand, one other observational ret¬rospective study was unable to demonstrate this benefit (Glueck CJ et al 2004).
Mechanisms put forward to explain this are a decrease in serum androgens, an improve¬ment in uterine vasculature (decreasing PAI 1 and increasing IGFbp1 and glycodeline), weight loss, or an improved luteal phase progesterone.
Metformin could be carefully assessed in PCOS patients undergoing IVM, as the miscarriage rate is high and it could be related to endocrinologic disturbance of PCOS that may be improved by metformin.
On the other hand, the low implantation rate observed in IVM must be an intrinsic drawback of IVM rather than a PCOS characteristic. Even if a recent study found a ben¬eficial effect of metformin over porcine oocytes in vitro, it may not improve overall implanta¬tion rates.
GnRH pumps or GnRH agonists
A meta-analysis was unable to determine any significant effect of the GnRH pump when used in PCOS patients (the patient numbers were too small). However, the pump has been shown to normalize LH levels in an observational study of 13 anovulatory PCOS women. As the high mis¬carriage rate observed in PCOS has been linked to high LH levels, it may be possible to improve implantation rates and decrease miscarriage rates.
Blastocyst transfer
The experience of IVM in The Family Federation of Finland is novel. In this center, the use of ICSI is reserved for masculine infertility. This restric¬tive use of ICSI decreases the fertilization rate and the number of embryo transfers, but the clinical pregnancy rate per embryo transfer is much higher so that the clinical pregnancy rate per immature oocyte retrieval is not significantly different.
Blastocyst transfer shows a high implantation rate when used in conventional IVF, presumably by better selection of embryos with the greatest developmental potential. Prolonged culture may be a good selection tool for the developmental potential of embryos generated from IVM oocytes.
CONCLUSIONS
Because it avoids OHSS and because it is less expensive, IVM might become an alternative to conventional IVF. Outcomes have already
improved. However, the main drawbacks remain a high cancellation rate, a low implantation rate, and a high miscarriage rate. 17β-Estradiol and metformin may be of help, but the future must go to embryo selection by prolonged (blastocyst) culture.