Fig 1. The frequency of ‘8’-shaped hatchings in mouse blastocysts was higher in in vitro cultured groups than the in vivo developed group.

(A) Representative images of pre-implantation embryos show the dynamic hatching process at day 4 (expanded blastocysts), day 4.5 (hatching blastocysts), and day 5 (hatched blastocysts) after fertilization. White arrows indicate ‘U’-shaped hatching blastocysts with large openings. Black arrows indicate ‘8’-shaped hatching blastocysts. The scale bar is 100 μm. (B) Images of ‘U’-shaped hatching and hatched blastocysts with large zona openings in the in vivo developed group (left panel) and ‘8’-shaped hatching and hatched blastocysts in both in vitro cultured groups (i.e., the in vivo fertilization group and the in vitro fertilization group, middle and right panels, respectively). The scale bar is 50 μm. (C) Comparison of hatching blastocysts exhibiting ‘8’-shaped and ‘U’-shaped hatching in the three groups. All the percentages are fractions based on the total number of expanded blastocysts for each group. **P < 0.01. (D) Comparison of hatched blastocysts exhibiting ‘8’-shaped and ‘U’-shaped hatching in the three groups. All the percentages are fractions based on the total number of hatching blastocysts for each group. *P < 0.05, **P < 0.01.