[Biology of medically assisted reproduction]

The biological techniques utilized in IVF are divided into several stages: conditioning of the gametes, in vitro fertilization proper, culture of ova and embryos, freezing of gametes and embryos. Conditioning oocytes obtained by follicular fluid aspiration is extremely simple, but oocyte maturity can neither be diagnosed very accurately nor improved in vitro. Several methods can be used to condition spermatozoa, but these methods have limitations: normospermia, for instance, cannot be obtained with sperms of poor quality. In vitro fertilization proper is relatively easy to perform, at least with mature oocytes, but the diagnosis of fertilization, especially abnormal fertilization, is not always reliable. The quality of the embryos obtained raises a major problem: their equipment in chromosomes is unassessable, and their viability can only be roughly evaluated.