The experience of extended in vitro human embryo cultivation in a culture medium containing endometrium cells. A pilot study

BACKGROUND: At present, the knowledge on initial human embryogenesis stages is limited to the period of development from zygote to blastocyst. The creation of models based on the interaction between the embryo and endometrium in vitro, which accurately imitate the in vivo processes, represents the major way for implantation and post-implantation evaluation. Currently, no reports have been made on models reflecting the both processes simultaneously: the interaction of the embryo with the substrate, which represents many aspects of normal implantation, and the early post-implantation embryo development. The creation of a relevant model would allow investigation of implantation and early post-implantation processes as a whole.

AIM: The aim of this study was to evaluate the vitality and developmental potential of human embryos from the day 6 blastocyst stage during their extended co-incubation with the endometrium in a culture medium specifically designed for cultivation to the blastocyst stage.

MATERIALS AND METHODS: Embryos obtained in assisted reproductive technology programs were cultivated from the day 6 blastocyst stage up to 14 days of development in vitro in a culture medium designed for cultivation to the blastocyst stage, in the presence of endometrium cells. On day 14 of development, embryos and endometrial samples were first evaluated under an inverted microscope using Hoffman modulation contrast, then transferred to a special mold and impregnated with paraffin for cytoblock preparation. Obtained blocks were sliced, stained with hematoxylin and eosin and morphologically assessed.

RESULTS: The first sample visual assessment on day 14 of cultivation in a culture medium with endometrium cells revealed a viable developing embryo with no signs of degradation. During the histological examination, the endometrial sample corresponded to the secretory phase of the cycle. The morphological assessment of the conceptus detected trophoblast cells. The second sample visual assessment on the day 14 of cultivation in a culture medium with endometrium cells revealed a viable embryo with no signs of degradation, which was in direct contact with the endometrial component. A histological examination detected a secretory endometrial fragment of the surface (luminal) epithelium. During the morphological assessment of the embryo, trophoblast cells were detected.

CONCLUSIONS: The data obtained indicate the ability of the embryo to further develop from the day 6 blastocyst stage up to 14 days in a culture medium specifically designed for cultivation to the blastocyst stage, in the presence of endometrium cells. The latter can serve as an experimental model for both in vitro endometrial receptivity evaluation and intercellular interactions during implantation investigation.