Objective
Oxygen inside the female genital tract varies from 2-8% which is the optimum oxygen tension needed for embryo development. The beneficial effects of 5% oxygen tension compared to the atmospheric tension (20%) on embryo development have been reported in animal models. However, the effect of lower or slightly higher oxygen tension on in vitro embryo development is still under investigation. Our objective is to compare the effect of 4 different oxygen tensions (3%, 5%, 8% and 20 %) on mouse embryo developmental parameters.
Design
Experimental animal study.
Materials and Methods
A total of 407 two-cell stage fresh mouse embryos were harvested from (C57BL/6J) female mice after superovulation and timed natural mating. Embryos were randomly cultured in four different oxygen concentrations; 3%, 5%, 8% ( in triple gas incubator with 6% CO2 and 91%, 89%, 86% N2 respectively) and 20% (in conventional incubator with 6% CO2) at 37°C. Embryos were cultured in groups of 5-10 in a 50 ul droplet of culture media under an oil overlay. Embryo morphology and development were monitored daily until day 4. Chi-square test was used for comparison between the 4 groups. P< 0.05 was considered significant.
Results
| Day 4 | 3%(n=95) | 5%(n=95) | 8%(n=107) | 20%(n=110) |
|---|---|---|---|---|
| Total blastocysts n(%) | 54(57%) | 72(76%) | 89(83%) | 67(61%) |
| Hatching blastocyst | 20% | 81% | 19% | 30% |
| Morula | 8 | 3 | 3 | 11 |
| <8 cells | 9 | 8 | 10 | 2 |
| Degenerated embryos | 24 | 12 | 5 | 30 |
On day 2, embryo fragmentation was significantly higher at 3 and 20% oxygen tension compared to that at 5 and 8% tension (P<0.05). On day 4, the total number of blastocysts at 8% oxygen tension was significantly higher than the 3 and 20% groups (P <0.001), but similar to that in the 5% group. However, the number of hatching embryos using 5% oxygen tension was significantly higher compared to all other groups (3%,8%, and 20 %) (P <0.001).
Conclusions
Our preliminary results showed that mouse embryos cultured under 5% oxygen tension have the best development and are more likely to blastulate, hatch and have better morphology compared to both lower and higher oxygen tensions. Further research is recommended with a larger sample size to confirm these findings.