Ovarian stimulation and embryo quality

To study the effects of different ovarian stimulation approaches on oocyte and embryo quality, it is imperative to assess embryo quality with a reliable and objective method. Embryos rated as high quality by standardized morphological assessment are associated with higher implantation and pregnancy rates. However, embryo morphology on day 3 after fertilization is not a reliable indication of a normal chromosomal constitution. Therefore, using embryo morphology as the sole parameter for embryo quality is not ideal. Screening of embryos for chromosomal aneuploidies before transfer can be used to assess the chromosomal competence of embryos, which has been shown to have a direct relationship with the approach used for ovarian stimulation. However, gene expression analysis of cumulus granulosa cells is a promising non-invasive technique for determining embryo quality. Cumulus cells are closely associated with oocytes, and oocyte–cumulus cell communication is vital to oocyte development. Cumulus cells respond to both gonadotrophins and paracrine factors from oocytes, with a distinct gene expression pattern. Future approaches analysing the expression of relevant genes in cumulus cells using real-time polymerase chain reaction may enable us to monitor the consequences of different stimulation protocols and identify the underlying molecular mechanisms by which they influence oocyte/embryo quality.