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| image credit: johnfriedmann.com |
As the early embryo passes through the morula stage osmotic movements of water will eventually form a blastocoel inside the developing blastocyst1. This water should be removed before vitrification by means of dehydration in high osmolality vitrification solutions. The dehydration process starts during exposure to the first solution with cryoprotectants and continues in the vitrification solution.
When exposing the embryo to cryoprotectants in the vitrification solutions for too long a time it results in toxicity. To reduce the amount of water to be replaced and also time in the vitrification solutions blastocysts can be collapsed before dehydration.
Spontaneous collapse is common
Blastocysts often collapse spontaneously during manipulation, for example during pipetting. But if this does not happen blastocyst collapse can be induced either by a laser pulse between two trophectoderm cells or by introducing a narrow pipette into the blastocoel.
