Sperm/egg binding patterns and oocyte cytology in retrospective analysis of fertilization failure in vitro

Abstract

Failures of fertilization in in-vitro fertilization have been often linked to visually recognizable defects in spermatozoa, and occasionally to anti-sperm antibodies. However, some total failures and the frequent lack of fertilization in some eggs of normal appearance (partial failure) often remain unexplained. Simple evaluation of the configuration of sperm binding to the zona pellucida and of the oocyte features revealed by acetic alcohol fixation and lacmoid staining, may provide diagnostic clues in this respect. Among 25 cases of unanticipated total failure, this approach identified some men with normal semen analyses whose spermatozoa displayed either a total inability to bind to the zona or, after binding, an inability to intrude into the zona matrix. However, in 10 of these cases significant numbers of spermatozoa were bound to and intruded deep into the zona, a pattern consistent with the possibility of an egg defect, specifically a resistance to the passage of spermatozoa past the inner portion of the zona pellucida. Such a block also appeared to be the main cause of fertilization failure among 442 unfertilized eggs from 154 partial failure patients. As in the total failures, the inability of apparently competent spermatozoa to penetrate the zona was often associated with ooplasmic anomalies (refractile bodies, extra groups of chromosomes, chromatin rings or masses, one or more pronuclei with one or no polar bodies, and other occasional anomalies). These anomalies occurred in 79.4% of this unfertilized oocyte subset, in contrast to a 27.4% incidence in 238 oocytes not fertilized because of sperm defects. Simple retrospective assessment of sperm binding patterns and oocyte cytology can be a valuable complement to semen analysis in diagnosis of fertilization failure in vitro.

fertilization failure, IVF, oocyte cytology, spermatozoa, zona pellucida binding