HUMAN GAMETE FUSION TEST - AN EXPERIMENTAL-MODEL FOR ASSESSING THE FUSION POTENTIAL OF SPERM FROM NONFERTILIZING NORMOSPERMIC PATIENTS

Objective: To develop an experimental model for assessing the ability of sperm to bind and subsequently fuse with the oolema and to use this test for evaluating the fusion potential of nonfertilizing human sper m. Design: Aged human oocytes (n = 108) were denuded of their zonae an d loaded with DNA-specific bisbenzamidazole fluorochrome. Sibling oocy tes were inseminated by semen samples from either normospermic patient s (study group; n = 12) who have repeatedly failed to achieve fertiliz ation in vitro or patients demonstrating high fertilization rates (con trol; n = 12). Gamete fusion was ascertained by fluorescent microscopy and validated by scanning electron microscopy. Test results were anal yzed in relation to current partial zona dissection treatment outcome. Setting: Infertility and IVF Unit of an academic tertiary referral me dical center and university-based basic research laboratory. Results: In samples achieving fertilization by partial zona dissection (7/12; 9 % to 23% fertilization rate), the mean numbers of fused spermatozoa we re similar to those of the control (2.1 compared with 2.6) and signifi cantly higher than in the partial zona dissection-failed fertilization subgroup. In six of seven cases in which partial zona dissection yiel ded embryos, fluorescent spermatozoa were detected on the oolema, wher eas in all but one partial zona dissection-failed cases gamete fusion was not observed. Conclusions: The suggested human gamete fusion test may help focus on specific sperm dysfunction in nonfertilizing patient s. It correlates well with the outcome of partial zona dissection-assi sted IVF trials and may provide useful information before this treatme nt is attempted.