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.

Polar body morphology and spindle imaging as predictors of oocyte quality.

It has been suggested that first polar body (PBI) morphology reflects oocyte competence. Oocytes with an intact normal-sized PBI have been described as generating better day 2 embryos, higher blastocyst yield, and increased pregnancy and implantation rates. In other studies, PBI morphology was found to be unrelated to fertilization rate, embryo quality, and blastocyst formation. In a prospective analysis, the predictive value of the PBI was investigated by comparing the development of oocytes retrieved from intracytoplasmic sperm injection patients and displaying different PBI morphology, classified according to the following characteristics: normal size and smooth surface (I), fragmented (II), rough surface (III), or large size (IV). Fertilization rates were 59, 57, 64 and 60% respectively. No significant differences were found between the various groups. The proportions of high quality (grade A) day 2 embryos were also comparable among groups I-III (14, 12 and 17% respectively), while the low number of grade A embryos in group IV (two embryos) did not allow comparison with the other classes. These data do not suggest that PBI selection can contribute to identification of embryos with high developmental ability. In order to establish alternative criteria for oocyte selection, a metaphase II (MII) spindle analysis was also conducted via Polscope. In oocytes of patients of different age, spindle retardance (which reflects the high order and density of microtubules) was compared with parameters of embryo development. In aged patients, a trend was observed between low retardance and poor embryo quality, although in general the association between retardance and oocyte developmental performance did not reach statistical significance.