ART failure: oocyte contributions to unsuccessful fertilization

Abstract

BACKGROUND: The complexity of fertilization failure during assisted reproductive technologies (ART) is often under-appreciated, as this failure can occur at any number of essential mechanistic and cellular events. Importantly, successful fertilization is heavily dependent upon inherent qualities of the oocytes, and thus reliant upon fidelity of oocyte maturation. METHODS: Pubmed and medline were searched up to April 2008 for papers on oocyte fertilization and its mechanistic components. References to clinical/human studies were selected wherever possible. RESULTS: Successful oocyte maturation cannot simply be determined via visual assessment of polar body extrusion, but rather entails coordination of numerous cytoplasmic processes not readily observed. Proper regulation of intraoocyte signaling cascades is crucial for sufficient production and storage of carbohydrates and proteins, successful relocation of organelles and regulation of metabolic pathways required for an apparently mature metaphase II oocyte to complete subsequent fertilization events; such as cumulus penetration, sperm/oocyte binding, fusion, oocyte activation, sperm processing and pronuclear (PN) formation. Regulation of oocyte maturation begins during oocyte growth and is intimately connected with events influencing folliculogenesis. Therefore, the oocyte is subject to a multitude of potential effector impacting fertilization potential and developmental competence long before encountering the artificial environment of the IVF laboratory. CONCLUSIONS: Although meticulous care and continued research is essential for future improvement, failure to fertilize and properly form PN following clinical ART is likely to be dependent on historical events in oocyte maturation, not easily explained or prevented through simple modification of contemporary laboratory protocols.

Analysis of clinical outcomes with respect to spermatozoan origin after artificial oocyte activation with a calcium ionophore

“…Oocyte activation is a crucial step in successful fertilization following sperm-oocyte fusion, and it induces calcium oscillations that raise the intracellular calcium levels in the oocyte [5]. The initial ooplasm calcium concentration increases within a few minutes of sperm-oocyte fusion, after which a sperm-derived factor (the oscillator) maintains this oocyte calcium level during normal fertilization [6].…”

How to Repair the Oocyte and Zygote?

“…The use of these approaches is, however, very wide and promising. With them, we can, for example, eliminate or almost eliminate mutated mtDNA, prevent oocyte aneuploidies, improve the quality of oocytes with poor morphology or low number of mitochondria [34][35][36] and eventually solve some problems with causes that are not yet known [37,38]. Clearly, one must take the risk and compare it with the potential benefits.…”

Pregnancy Outcomes in Infertile Women with Polycystic Ovaries following Intracellular Sperm Injection

“…As for oocyte morphological normality, oocytes with smooth granular or transparent cytoplasm, single polar body, appropriate zona pellucida thickness, and proper perivitelline space (PVS) were considered normal and consequently used in ICSI. Conversely, oocyteswith coarse granular, non-homogeneous, dark (brownish-blackish), or fragmented cytoplasm; distorted oolemma;or non-spherical (irregular shape) with or without large PVS were considered degenerated [10][11][12][13].…”