The effect of modification of the embryo culture environment on human embryo development

Abstract

The embryo culture environment is important for embryo development. Continual improvement of the embryo culture system is important to increase the success rate of ART. In order to optimize the embryo culture environment, it is effective to reduce various stress on in vitro embryo culture and not to lower the potential of the embryo (Wale and Gardner, 2015). We have continued to improve the embryo culture environment by revising culture medium, culture devices, and medium exchange. We currently conduct group culture combining single-culture medium and Well of the Well (WOW) culture dish. We evaluated the current culture environment by comparing preimplantation development using a conventional method (sequential medium and single culture using a standard dish) and the current method (single-culture medium and group culture using a WOW dish). Prospective cohort study. In the current method, we used a WOW culture dish (LinKID culture dish; DNP). For the current method, we used 101 embryos from 29 cases, which patients otherwise had wanted to dispose of but consented to be used for research after they were cryopreserved at the pronuclear stage. For the conventional method, we used the clinical outcome of 207 embryos, which were collected at the same time as the 101 embryos, as described above. In the conventional method, embryos were cultured as single embryos up to the blastocyst stage in 15 μl of sequential medium (SAGE) with medium changes on Days 3-5 using a standard dish. In the current method, embryos were thawed and cultured (2 to 10 embryos per dish) in 60 μl of single-culture medium (Nakamedical) using a WOW dish without medium change. In both systems, embryos were cultured up to Day 6. The rate of blastocyst formation (≥Blast3), good-quality blastocyst (≥Blast3BB), and embryo utilization (≥Blast3 (excluding CC)/cultured embryo) were compared using a chi-square test. The blastocyst rate was significantly higher in the current method than the conventional method (52.2% vs. 67.3%). The rate of blastocyst formation and good-quality blastocysts at Day 5 were significantly higher in the current method (26.6% vs 43.6%; 25.6% vs 38.6%). Furthermore, the embryo utilization rate of the current method was significantly increased as compared with the conventional method (48.3% vs 62.4%). Exposure stress to oxygen has been reported to cause delay of embryo development (Wale and Gardner, 2010). Single-culture medium, which does not require medium change, decreases the operation outside the incubator compared with sequential medium, and it is thought that these stresses can be suppressed. Furthermore, the embryo development in group culture may be improved by a paracrine effect (Ebner et al., 2010). The changes in the culture environment improved the preimplantation occurrence.