Oocyte selection is a procedure that is performed prior to in vitro fertilization, in order to use oocytes with maximal chances of resulting in pregnancy. In contrast, embryo selection takes place after fertilization.

Techniques

Chromosomal evaluation may be performed. Embryos from rescued in vitro-matured metaphase II (IVM-MII) oocytes show significantly higher fertilization rates and more blastomeres per embryo compared with those from arrested metaphase I (MI) oocytes (58.5% vs. 43.9% and 5.7 vs. 5.0, respectively).

Also, morphological features of the oocyte that can be obtained by standard light or polarized light microscopy

Polarized light microscopy

Polarized light microscopy can mean any of a number of optical microscopy techniques involving polarized light. Simple techniques include illumination of the sample with polarized light. Directly transmitted light can, optionally, be blocked with a polariser orientated at 90 degrees to the...

. However, there is no clear tendency in recent publications to a general increase in predictive value of morphological features. Suggested techniques include zona pellucida

Zona pellucida

The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...

 imaging, which can detect differences in birefringence

Birefringence

Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...

 between eggs, which is a predictor of compaction, blastulation and pregnancy.