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Abstract
BackgroundImproved pregnancy, implantation, and birth rates have been reported after the use of reduced O2 concentration during embryo culture, mainly due to a reduction of the cumulative detrimental effects of reactive oxygen species. However, some studies have failed to report any positive effects. The objective of this meta-analysis was to evaluate the effect of a low-O2 environment on IVF/intracytoplasmic sperm injection (ICSI) outcomes.MethodsAll available published and ongoing randomised trials that compared the effects of low (~5%; OC~5) and atmospheric (~20%; OC~20) oxygen concentrations on IVF/ICSI outcomes were included. Search strategies included online surveys of databases from 1980 to 2011. The outcomes measured were fertilisation rate, implantation rate and ongoing pregnancy rates. The fixed effects model was used to calculate the odds ratio.ResultsSeven studies were included in this analysis. The pooled fertilisation rate did not differ significantly (P = 0.54) between the group of oocytes cultured at low O2 tension and the group at atmospheric O2 tension. Concerning all cycles, the implantation (P = 0.06) and ongoing pregnancy (P = 0.051) rates were not significantly different between the group receiving transferred sets containing only OC~5 embryos and the group receiving transferred sets with only OC~20 embryos. In a meta-analysis performed for only those trials in which embryos were transferred on day 2/3, implantation (P = 0.63) and ongoing pregnancy (P = 0.19) rates were not significantly different between the groups. In contrast, when a meta-analysis was performed using only trials in which embryos were transferred on days 5 and 6 (at the blastocyst stage), the group with transferred sets of only OC~5 embryos showed a statistically significantly higher implantation rate (P = 0.006) than the group receiving transferred sets with only OC~20 embryos, although the ongoing pregnancy (P = 0.19) rates were not significantly different between the groups.ConclusionsDespite some promising results, it seems too early to conclude that low O2 culture has an effect on IVF outcome. Additional randomised controlled trials are necessary before evidence-based recommendations can be provided. It should be emphasised that the present meta-analysis does not provide any evidence that low oxygen concentration is unnecessary.
Highlights
Improved pregnancy, implantation, and birth rates have been reported after the use of reduced O2 concentration during embryo culture, mainly due to a reduction of the cumulative detrimental effects of reactive oxygen species
The results showed that embryos cultured in a 5% O2 environment consistently resulted in higher rates of implantation (106/247, 42.9% versus 82/267, 30.7%; a difference of 12.2% and a 95% confidence interval (CI) of 3.9-20.3, P = 0.005) and live births (66/115, 57.4% versus 49/115, 42.6%; a difference of 14.8% with a 95% CI of 1.927.0%, P = 0.043) when compared with rates among women whose embryos were cultured in an atmospheric O2 environment
The pooled fertilisation rates did not differ significantly between the group of oocytes that was cultured at OC~5 (73%, 7, 066/9, 682) and the group cultured at OC~20 (72.5%, 7, 495/10, 342) (P = 0.54; odds ratio (OR) = 1.02, 95% CI = 0.96-1.09)
Summary
Implantation, and birth rates have been reported after the use of reduced O2 concentration during embryo culture, mainly due to a reduction of the cumulative detrimental effects of reactive oxygen species. Some studies have failed to report any positive effects. The role of oxygen tension during the culture of gametes and embryos has been the subject of study in both animal models and humans. Following protocols from somatic cell culture techniques, the embryos of humans and other mammals have traditionally been cultured under. These results are associated with a reduction of the harmful effects of reactive oxygen species (ROS). The in vitro manipulation of gametes in embryos favours the generation of ROS as it involves the exposure of eggs and embryos to xenobiotics, disturbed concentrations of metabolic substrates, traces of transitional elements, light and high oxygen concentrations [20]
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