Reducing the time of co-incubation of gametes in human in-vitro fertilization has no beneficial effects.

Reports concerning the benefit of reducing the co-incubation time of gametes in connection with IVF have been conflicting. The present randomized study was undertaken to determine whether a reduced co-incubation time would improve the embryo development and consequently the pregnancy and implantation rates. Oocytes from 87 patients were collected and half the oocytes from each patient (n = 488, group A) were randomized to 2 h incubation and the other half (n = 504, group B) to overnight incubation. The oocytes were then cultured according to our standard procedure. Significant difference (P = 0.02) was observed between the two groups regarding fertilization rate and polyspermy (group A 72.5%, 3% and group B 80.5%, 6% respectively). However, no difference was observed in further development and morphology of the embryos. The two embryos with the best morphological score were selected for transfer. No significant difference was found between the different transfer groups regarding positive serum HCG and implantation rate. CONCLUSION: The present results and results from previously published studies indicate that the most important factor in connection with the culture method currently used is the amount of sperm added for co-incubation. This should be optimized to reduce the concentration of harmful sperm waste products and create optimal culture conditions.