Abstract
Hatching out from the zona pellucida (ZP) is a crucial step for blastocyst implantation and development. However, it is still unknown whether the location of the hatching site relative to the inner cell mass (ICM) affects embryo implantation and foetal development. Here, we classified hatching blastocysts into three categories, 0° ≤ θ ≤ 30°, 30° < θ ≤ 60°, and 60° < θ ≤ 90°, in which θ is determined based on the relative position of the hatching site to the arc midpoint of the ICM. Non-surgical embryo transfer (NSET) devices were employed to evaluate blastocyst implantation and embryo development. Of 1,827 hatching blastocysts, 43.84%, 30.60%, and 21.67% were categorized as 30° < θ ≤ 60°, 0° ≤ θ ≤ 30°, and 60° < θ ≤ 90°, respectively. Embryos with different hatching sites showed no distinct differences in blastocyst implantation; surrogate female pregnancy; embryo development to term; litter size, or offspring survival, gender, or body weight. Our results indicate that mouse blastocyst hatching site is not randomly distributed. Embryo implantation and development are not correlated with the blastocyst hatching site in mice. Thus, assessment of the blastocyst hatching site should not be recommended to evaluate mouse blastocyst implantation and developmental potential.
Highlights
Hatching out from the zona pellucida (ZP) is a crucial step for blastocyst implantation and development
These two hatching patterns were both observed in in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) embryos, they have no effect on embryo implantation
The results showed that significantly more blastocysts hatched from the site 30° < θ ≤ 60°, whereas different hatching sites had no influence on subsequent implantation; surrogate female pregnancy; embryonic development to term; litter size; or offspring survival, gender, or body weight
Summary
Hatching out from the zona pellucida (ZP) is a crucial step for blastocyst implantation and development. Successful embryo implantation is determined by three factors: embryo quality, the receptivity of the uterine endometrium, and the intricate relationship between the two[5,6] It is still a subject of debate whether the blastocyst hatching site has an influence on the final hatched rate. Observational studies demonstrated that the natural hatching site in humans usually develops at a position close to the blastocyst inner cell mass (ICM)[7,8]. Others found that ZP opening close to the ICM was associated with a higher implantation and pregnancy rate in humans[12] It is still not known if the hatching site determines embryo implantation and foetal development. The purpose of this study is to assess the implantation and foetal development of blastocysts with different hatching sites after transfer by a non-surgical approach. The methodology involved in our study and the classification of blastocyst hatching sites may provide guidance for future human blastocyst hatching analysis
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