Morphological Selection of Gametes

Abstract

Methods of selecting gametes before the intracytoplasmic sperm injection (ICSI) technique are of paramount importance, especially where for religious, ethical or legal reasons the production of supernumerary embryos has to be avoided. In these circumstances, in fact, the research has to be focused on the identification of early markers of embryo quality at the oocyte and sperm stage before fertilisation. Oocyte quality can be influenced by several factors such as controlled ovarian hyperstimulation protocols, pharmaceutical preparations and perifollicular vascularisation. Several intracytoplasmic and extracytoplasmic abnormalities have been described, but whether these abnormalities might be predictive of oocyte competence is controversial and the selection methods proposed are still poorly effective. Recently, we have observed that oocyte morphological abnormalities might be indicators of oocyte competence. An abnormal first polar body (but not fragmented), a large perivitelline space, increased cytoplasmic granularity, and the presence of a centrally located granular area seem to have a negative effect on the oocyte potential to fertilise, cleave, and/or develop into a viable embryo. Sperm morphology can be more accurately observed at high magnification using an inverted microscope equipped with Normarski optics (1000× magnification under mineral oil) and a digital system in order to reach a final magnification of approximately 6300×. Single sperm nuclear abnormalities based on strict selection criteria seems to have a clear negative association with ICSI outcome. The possibility of observing the spermatozoa in real time at higher magnification might also be a good opportunity to study the relationship between particular sperm defects and ICSI outcome. In addition to morphology, it has been suggested that spermatozoa selection might be performed on the basis of its biochemical ability to bind to solid hyaluronic acid. However, it must be underlined that prospective randomised studies are necessary to confirm the preliminary results regarding the efficacy of the described criteria proposed, to morphologically select gametes prior to in vitro insemination.