Morphokinetic characteristics of preimplantation development of human donor embryos

Background: The introduction of time-lapse incubators into assisted reproductive technology practices provides a detailed examination of human pre-implantation embryo development. The continuous time-lapse filming technology is used to determine prognostic markers of embryo viability and implantation potential based on morphokinetic parameters. At present, the main time intervals for morphokinetic events during the pre-implantation phase of human embryo development have been documented primarily in embryos from infertile patients, with limited data available concerning the development of donor embryos. In this regard, it becomes relevant to follow the early development of such embryos and describe the embryonic development timeline using time-lapse technology.

Aim: The aim of this study was to determine the time intervals of critical events in the pre-implantation development of human donor embryos.

Materials and methods: The material for the study was 18 donor embryos obtained after fertilization of donor oocytes with donor sperm. The embryos were cultured for 140 hours in an EmbryoVisor time-lapse incubator (Westtrade Ltd., Russia).

Results: The video image analysis of diploid donor embryo development showed that the disappearance of both pronuclei occurred at 22.2 (21.0–25.4) hours post fertilization, the 2-cell embryo stage was observed at 24.5 (23.4–27.3) hours post fertilization, the 4-cell embryo stage at 35.9 (34.6–38.6) hours post fertilization, and the 8-cell embryo stage at 52.8 (49.0–58.8) hours post fertilization. Morula formation occurred at 86.0 (76.9–95.4) hours post fertilization, and complete blastocyst formation was recorded at 107.0 (99.1–114.3) hours post fertilization. Triploid embryos tended to have a delay in the cleavage stage and a shorter compaction phase, yet generally developed within similar timeframes as diploid embryos.

Conclusions: The analysis of video recordings obtained after culturing donor embryos in the time-lapse incubator allows for comparing the morphokinetic parameters of pre-implantation development of the donor embryos, taking into account their ploidy. The checkpoints in the development of pre-implantation embryos from the zygote stage to blastocyst formation are characterized. A tendency is noted for earlier disappearance of pronuclei, a delay at the cleavage stage from four to eight cells, and a shorter compaction stage in the donor embryos with impaired ploidy. Various anomalies in the development of such embryos are also described. Special attention should be paid, perhaps, to embryos that do not fit into the established development intervals, exhibit anomalies such as reverse cleavage, direct division from one to three cells, and excessive fragmentation, or stop developing at one point or another, since this may indicate anomalies in the embryo’s genome such as, for example, aneuploidy. Timely identification of these deviations may lead to the exclusion of embryos with morphokinetic abnormalities from transfer, thereby favoring the selection of normally developing embryos to enhance implantation success and promote ongoing pregnancies. An increase in the sample of donor embryos under study, information on their genetic status and the clinical results of pregnancy after embryo transfer, and further accumulation of data will augment the ability to predict embryo implantation potential without the use of invasive methods.