Effect of oocyte quality and sperm characteristics on the number of spermatozoa bound to the zona pellucida of human oocytes inseminated in vitro.

Sperm characteristics and oocyte quality may play a role in in vitro fertilization. The objective of this paper is to analyze the effect of the quality of oocytes, the husband's semen characteristics, and category of the couple's infertility on the number of spermatozoa bound to the zona pellucida. One hundred eighty-one oocytes which failed to fertilize or failed to cleave were fixed in 2.5% glutaraldehyde 40 to 60 hr after insemination in vitro and examined under interference microscopy and the number of sperm bound to the zone pellucida was determined. The means +/- SD of sperm bound to mature, immature, and atretic oocytes were 51.0 +/- 50.7, 7.3 +/- 12.1 10.4 +/- 17.8, respectively. Fertilized mature oocytes (81.0 +/- 53.3) had a significantly higher number of sperm bound to zonae compared to unfertilized oocytes (41.8 +/- 47.3). It is concluded that the number of sperm bound to zonae is functionally important. The sperm motility and the number of motile sperm used to inseminate oocytes were significantly correlated with the number of sperm bound to zonae, whereas sperm morphology and sperm concentration did not correlate. This study supports the notion that sperm motility is the single most important factor influencing fertilization of human oocytes in vitro.