Document Type : Original Article
The purpose was to investigate the effect of the duration of gamete incubation on fertilization rate, embryo cleavage, and embryo quality before and after freezing in mice.
Materials and methods
Ovulated oocytes collected from superovulated mice after ip injection of PMSG and hCG were divided randomly into control and experimental groups. Oocytes from the control group were inseminated for six hours and the experimental group were inseminated for one hour, respectively. The differences in fertilization rates, embryo cleavage and percent of good quality embryos in four grades (A, B, C, D) were analyzed. Finally, two cell embryos were frozen; and after thawing, the quality of embryos from the two groups were compared.
There was no difference between the two groups in regards to fertilization and cleavage rates. However, the proportion of grade A embryos was significantly higher among the experimental group (41.7%) when compared to the control group (19%). Also the proportion of grade D embryos was significantly (p=0.04) lower in the experimental group (8.3%) as compared to the control group (23.8%). In addition, percentage of good quality embryos in the experimental group did not decrease after freezing (p=0.3), however the percentage of good quality embryos were significantly decreased after freezing in the control group (p=0.01).
Insemination of oocytes for a short period produced embryos of superior quality than insemination for a longer period in the experimental group . Also, the effect of freezing on embryos produced from short insemination was less than the long insemination period. After freezing, a higher percentage of good quality embryos survived post thawing in mice.