Chapter 8 - Noninvasive Morphological Selection of Oocytes

Summary

Gamete and embryo selection finalization for the improvement of clinical efficiency and efficacy represents the “holy grail” of assisted reproduction technologies (ART). Embryos are routinely assessed and selected or ranked for embryo transfer on the basis of static or dynamic morphological criteria or, less frequently, their chromosomal status. Sperm are also subject to methods of isolation from semen to pre-select a population with improved motility and morphology to maximise the chances of fertilisation. Oocyte selection, i.e. selective use based on different morphological patterns which are presumed to be prognostic of different developmental potential, is a less accepted and practiced concept in in vitro fertilisation (IVF) laboratories. Two major reasons concur to make oocyte selection controversial: i) the usually limited number of oocytes retrieved in each ovarian stimulation cycles; ii) the uncertainty of possible associations between different dysmorphisms and downstream impacts on laboratory or clinical outcomes. Oocyte dysmorphisms can affect both the intra- and extracellular morphological domains of the mature oocyte. Oocyte abnormalities can also occur with different degrees of severity and different localisations. In addition, in the absence of specific non-invasive markers, some types of dysmorphisms may be difficult to discriminate by simple morphological observation. All these factors complicate oocyte morphological selection according to appropriate standards of reproducibility and precision, preventing its adoption as a universally accepted procedure.