hatching blastocyst
Embryo at the stage where it begins to emerge from the zona pellucida prior to implantation.
Full Definition
A developmental stage where the blastocyst starts to break through and emerge from the zona pellucida, the protective shell surrounding the embryo. This natural hatching process typically occurs around day 6-7 of development and is necessary for the embryo to implant in the endometrium. The trophectoderm cells create small tears in the zona pellucida, eventually allowing the entire blastocyst to escape. In some cases, assisted hatching may be performed in the laboratory to help embryos with thick or hardened zona pellucida complete this process.
Usage
Usage note: Distinguish from 'hatched blastocyst' (completely emerged) and 'expanded blastocyst' (pre-hatching stage).
In Context
- "The hatching blastocyst showed excellent morphology with clear inner cell mass definition." — embryology report
- "Transfer of a hatching blastocyst may indicate optimal timing for implantation." — clinical note