Morphometrical study of mouse pre-implantation embryos: comparison of in vitro- and in vivo-produced embryos

Background and

The development of pre-implantation mammalian embryos in vitro is compromised, compared with those grown in vivo. Selecting embryos with a high implantation potential is one of the most important challenges in the field of assisted reproductive technology. The aim of this study was to postulate morphometrical characteristics of good quality embryos, with comparisons between in vivo and in vitro produced mouse embryos.

Embryos was obtained from NMRI female mice after super ovulation. In vivo developed 2-, 4- and 8-cell embryos; morulla and full blastocyst were isolated from mice on 18, 36, 52, 60, 72 and 96 hours after hCG administration respectively. Ham, s F10 medium was used for in vitro culture of embryos. External and internal diameter of embryos, zona thickness and number of cells in full blastocysts were evaluated and compared between in vivo and in vitro groups.

External and internal diameter and zone thickness in oocyte and zygotes were 99.9µm, 75.4µm and 4.9µm respectively. These values did not change prior to the blastocyst stage in both in vivo and in vitro groups; but in full blastocyst stage, the diameter of embryos significantly increased and zone thickness decreased compared to prior stages in both groups (P<0.01). The diameter of full blastocysts of in vivo group (116.5 µm) were significantly larger than those of in vitro group (104.3 µm, P<0.05). Moreover, the full blastocysts of in vivo group had significantly more blastomeres (49), compared to in vitro group (43, P<0.05). Additionally, cultured embryos reached full blastocyst at 110 hours after hCG administration, while in vivo condition the time frame was 96 hours.

Based on the above results, embryo size and zona thickness can not predict embryo quality prior to blastocyst stage, however, in this stage; larger embryos and those that have more blastomere may show greater viability.