Effect of oxygen concentration on early cleavage of human embryos in vitro

Abstract

Reduced oxygen concentration has been shown to improve only the latter stages of preimplantation development of human embryos in vitro (days 4–6 of culture), resulting in higher incidence of blastocyst formation and higher number of blastomeres. Our study was focused on the effect of different O 2 concentrations on the cleavage kinetics and fragmentation rate during the first 2 or 3 days of in vitro culture. Embryos from 400 patients were cultured at 20% or 5% of O 2. Morphologic evaluation of embryos was performed at 39–42 h after insemination or ICSI for day 2 transfer and at 63–66 h for day 3 transfer, respectively. Data were analysed by χ 2 test. On day 2, the mean cell number of all embryos cultured at 5% O 2 was significantly higher ( p<0.05) than of those embryos cultured at 20% O 2 (3.62 vs. 2.87, respectively). The similar results were observed on day 3 (6.31 vs. 5.86, respectively, p<0.05). Fragmentation rate was significantly lower in the embryos cultured at 5% O 2 as compared with those embryos cultured at 20% O 2 (67.7% vs. 42.3% of embryos with less than 10% fragmentation, p<0.01). In conclusion, we have observed significantly faster kinetics of cleavage and lower fragmentation rate in the group of embryos cultured at lower O 2concentration (5%) as compared to embryos cultured at 20% of O 2 during the first 3 days of in vitro culture.