Reduction in exposure of human embryos outside the incubator enhances embryo quality and blastulation rate

Embryo quality is strongly dependent on the in-vitro culture environment. Conventionally, IVF/intracytoplasmic sperm injection (ICSI) embryos are examined microscopically every morning (from day 1 to day 6) to assess fertilization, cleavage and embryo quality. Consequently, the frequent exposure to non-optimal conditions outside the incubator may adversely affect embryonic viability and quality. Hence, this study investigated whether reduction of observation frequency outside the incubator can enhance blastocyst formation rate. A total of 285 IVF/ICSI cycles were divided into two groups. Embryos in the control group (103 cycles) were assessed out-of-incubator every day after insemination (day 1 to day 6; six times). In the experimental group (182 cycles), embryos were assessed four times, on days 1, 3, 5 and 6. The total blastocyst formation rate, day-5 blastocyst formation rate, proportion of good blastocysts and number of cryopreserved blastocysts per patient were significantly lower for the control group compared with the experimental group (42.5%, 31.4%, 50.7%, 1.72 ± 1.55 versus 52.6%, 40.7%, 60.1%, 2.64 ± 2.59, respectively, P < 0.05); although there were no significant differences in the proportions of good embryos on day 3, blastocyst formation rate on day 6, clinical pregnancy rate and implantation rate. Hence, reduction of the observation frequency of embryos outside the incubator can enhance embryo quality and blastocyst formation rate.