FROM THE CONVENTIONAL TO THE MILDER APPROACHES TO OVARIAN STIMULATION FOR IN VITRO FERTILIZATION
Background: In-vitro fertilization (IVF) is performed with oocytes collected in natural and stimulated cycles. Different approaches to ovarian stimulation have been employed worldwide. Fol- lowing the introduction of gonadotrophin realising hormone (GnRH) antagonists and strategies to reduce multiple birth such as single embryo transfer, there is an interest in the revival of natural and mild approaches to ovarian stimulation in IVF. Particulary mild ovarian stimulation aims to achieve cost-effective, patient-friendly regimens which optimize the balance between outcomes and risks of treatment.
Methods: Pubmed was searched up to 2009 for papers on natural, modified natural, mild and con- ventional IVF cycles.
Results: Data discussed in this review do not allow any conclusions to be drawn regarding the most optimal mild ovarian stimulation protocol. However, it is absolutelly clear that introduction of GnRH antagonists into clinical practice has allowed for the introduction of milder stimulation approaches for IVF treatment because of preventing premature luteinising hor- mone (LH) rise by competitive blockade of the GnRH receptors. Studies also show that mild exogenous gonadotrophins interference with the decrease in follicle-stimulating hormone ((FSH) levels in the mid-folicular phase was sufficient to override the selection of a single dominant follicle and enhance the most mature follicles to growth due to their increased sensitivity for FSH and acquired responsiveness to LH.
Conclusions: The implementation of mild stimulation and modified natural cycle into standard clinical practise appears to be justified, although more prospective studies are needed to find the most appropriate mild stimulation approaches.
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