Selecting an oocyte for in vitro fertilization involves assessing the quality of the oocyte which is usually done by accessing the morphological features of the oocyte. The major parts of the oocyte that are accessed for quality in terms of morphological characteristics are the cumulus cells, zona pellucida, polar body, perivitelline space, and cytoplasm; These are the main parts of the oocyte and are usually assessed by conventional microscopy. The size of an oocyte is another factor of the quality of the oocyte; Larger oocyte are usually more quality than smaller ones. 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. However, there is no clear tendency in recent publications to a general increase in predictive value of morphological features. Suggested techniques include
zona pellucida imaging, which can detect differences in
birefringence between eggs, which is a predictor of
compaction,
blastulation and pregnancy. Potentially,
polar body biopsy may be used for molecular analysis, and can be used for
preimplantation genetic screening. == References ==