The invasive and new non-invasive methods of mammalian oocyte and embryo quality assessment: a review

The quality of oocytes-embryos can be determined by several techniques, including morphological, molecular, cellular and biochemical ones. The morphological methods of female gamete or embryo quality assessment often use thе following in vitro manipulation procedures such as: in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro embryo production (IVP). However, these methods are highly subjective and the morphological classification of oocytes or embryos is not always compatible with their ability to grow and develop. Additionally, molecular biology methods are objective and present parametric results, which are more or less comparable to the real oocyte-embryo "health". Although these techniques enable us to determine markers of oocyte-embryo developmental potential, when applied they lead to destruction of the analysed cells. Therefore, the need still exists to search for new methods that will be highly objective (parametric) and, which is most important, non-invasive. In this review, the morphological and molecular methods of oocyte-embryo quality assessment are presented. Moreover, we described a new system based on microfluidic technology (Lab-on-Chip) which allows the creation of a new device for mammalian oocyte as well as embryo quality evaluation: by using their spectral characterisation following embryo transfer (ET) procedures in the cattle and the pig.