Exposure of embryos to oxygen at low concentration in a cleavage stage transfer program: reproductive outcomes in a time-series analysis.

Background: Embryos are exposed to oxygen at a concentration of 2% to 8% under in vivo conditions. Laboratory culture of embryos with oxygen at atmospheric tension impairs embryo metabolism and blastocyst development in several species. Indeed, a high rate of live births after a day 5 transfer has been obtained by lowering oxygen concentration in the incubator atmosphere, thus definitively proving the damaging effect of oxygen at atmospheric tension on late stage development of human embryos. Conversely, the possible beneficial effect of low oxygen tension on assisted reproductive technology (ART) outcomes in a selective cleavage stage transfer program remains controversial. Therefore, the present study validated the hypothesis that oxygen at reduced concentration may improve ART outcomes when cleavage stage embryos are transferred.

Methods: The effect of oxygen at atmospheric versus reduced concentration on laboratory and clinical outcomes of both in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles were compared. Evaluation of outcomes included fertilization, cleavage, and implantation rates. Clinical outcomes were also assessed in our analysis.

Results: From May 2010 to Mid-October 2010 357 ART cycles (ICSI n = 273 and IVF n = 84) were performed using atmospheric oxygen laboratory incubators while from Mid-October 2010 until March 2011 306 cycles (ICSI n = 224 and IVF n = 82) were carried out under low oxygen concentration. The multi-ovulation protocols were not significantly different between the two study periods. The medical and laboratory staff, the laboratory, and its procedures and the operating room did not differ between the two groups, neither did the culture media. For ICSI procedures, no significant difference in ART outcomes was found between the two culture conditions. For conventional IVF cycles, both fertilization rate (59 +/- 36 vs. 71 +/- 32, respectively) and proportion of embryos obtained (38% vs. 50%, respectively) were significantly improved under low oxygen condition.

Conclusions: Culture of embryos in oxygen at low tension improved ART outcomes during a selective cleavage stage transfer program.