The success rates of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are improved when the embryo culture occurs under conditions that provide low oxygen concentrations, show the findings of a new systematic review and meta-analysis.1
Optimizing the success of IVF and ICSI procedures currently is one of the main focuses of research in reproductive medicine, according to the authors. Improving the in vitro environment to which human embryos are exposed before implantation into the uterus is one such area of focus, they explain. Traditionally, human preimplantation embryos are cultured in laboratories using an atmospheric oxygen concentration, which is about 20%. However, the oxygen concentrations in the oviduct and the uterus range from 2% to 8%.2 To more closely mimic natural conditions, some laboratories have started to culture embryos at a lower oxygen concentration (about 5%), although doing so is associated with higher costs (incubators sensing both carbon dioxide and oxygen, plus the gases themselves, as well as nitrogen to purge oxygen from the incubator).
In a systematic review and meta-analysis of randomized controlled trials comparing embryo culture at low (about 5%) and atmospheric (about 20%) oxygen concentrations, researchers sought to determine which oxygen concentration most improves treatment outcomes. A total of 7 studies involving 2422 participants met inclusion criteria, but only 4 of those studies, which included a total of 1382 participants, provided sufficient data for a meta-analysis. The authors determined that the overall methodological quality of the included studies was low.
The meta-analysis showed that live birth rates were improved when the embryos were cultured in a low oxygen concentration setting (odds ratio, 1.39; P=0.05). The authors explain that in clinical practice, this translates to improving a 30% live birth rate achieved by using atmospheric oxygen concentration to a live birth rate of 32% to 43% using low oxygen concentration. The ongoing and clinical pregnancy rates were similar between study groups. Researchers also found that using low oxygen concentration during embryo culture was not associated with increased rates of multiple pregnancies, miscarriages, or congenital abnormalities.
The findings of this meta-analysis are more promising than the findings of another recent meta-analysis, which concluded that there is insufficient evidence to determine whether low oxygen concentration has any effect.2
- Current evidence indicates that culturing human preimplantation embryos in low oxygen concentration improves not only ongoing and clinical pregnancy rates but also live birth rates.