A prospective randomized controlled study of the effect of short coincubation of gametes during insemination on zona pellucida thickness

A prospective, randomized study was conducted to evaluate the thickness of zona pellucid a (ZP) after brief or standard exposure of human oocytes to spermatozoa, and to determine the correlation between ZP thickness, fertilization rate and embryo quality. The mean ZP thickness 48 h after insemination was found to be significantly less in fertilized oocytes than in non-fertilized oocytes in all treated groups (13.72 ± 3.0 μm and 15. 08 ± 2.5 μm, respectively; p < 0.007). Zona pellucida thickness correlated positively with embryo quality. Brief exposure of gametes was found to influence ZP thickness. The ZP was significantly thinner after brief and intracytoplasmic sperm injection (ICSI) exposure of oocytes to spermatozoa than after standard in vitro fertilization (IVF). The mean ZP thickness 24 and 48 h after fertilization was significantly greater in standard IVF (16.43 ± 2.8 μm and 15.22 ± 2.7 μm, respectively) than in either the brief exposure or ICSI groups (12.78 ± 2.4 μm and 13.01 ± 3.5 μm vs. 13.46 ± 2.2 μm and 13.16 ± 2.4 μm; p < 0.0001).