Purpose: To determine whether embryos cultured with a low oxygen level (2%) brought about beneficial effects on the outcome of ART.
Methods: This is a sequential case-control embryo-culture study. Embryos were cultured either with a gas mixture containing 2% O2, 5% CO2, and 93% N2 (low-oxygen group) or 5% O2, 5% CO2, and 90% N2 (conventional group). From January 2008 to September 2008, 873 fertilized oocytes were obtained from 250 patients in the low-oxygen group and from October 2008 to March 2009, 730 fertilized oocytes were obtained from 213 patients in the conventional group. The outcomes of ART were compared between two groups.
Results: The cleavage rate in the low-oxygen group (94.4%) was similar to that (94.7%) in the conventional group. The mean number of blastomeres on Day 3 in the low-oxygen group (mean ± SE) was 6.5 ± 1.9, and this was significantly lower than in the conventional group (6.8 ± 1.9, p < 0.05). Moreover, the low-oxygen group produced worse quality embryos, on the basis of the significantly higher embryo grade 2.1 ± 0.6 versus 1.9 ± 0.6, p < 0.001, in 5% oxygen. The pregnancy and miscarriage rates in the low-oxygen group were 22.3 and 20.8%, respectively, which were statistically similar to the outcomes in the conventional group.
Conclusions: Overall, culture of embryos at the low oxygen level did not significantly improve ART results compared with embryos grown in 5% oxygen. The study suggests that a low oxygen level worsens embryo morphology but does not impair embryo viability.
Keywords: ART; Embryo development; Embryo quality; High oxygen; Low oxygen.