EXPLANATION
Laser induced cell separation during trophectoderm biopsy is the only biologically irreversible step because it causes direct photothermal ablation of cellular membranes and intercellular junctions, resulting in permanent loss of viable embryonic cells.

At the cellular level, laser severing disrupts plasma membranes and junctional complexes, irreversibly removing trophectoderm cells from the embryonic architecture with no possibility of reintegration or functional compensation.

At the molecular level, localized laser energy exceeds the thermal tolerance of biological macromolecules, producing lipid bilayer rupture, irreversible protein denaturation, cytoskeletal depolymerization, permanent destruction of junctional proteins (cadherins, claudins, occludins), and uncontrolled ionic flux, collectively triggering immediate cell death and precluding recovery.

In contrast, zona breaching affects only the acellular zona pellucida, blastocoel collapse is a reversible biophysical fluid shift regulated by intact ion transport mechanisms, and cell aspiration remains reversible until membrane ablation occurs.

Therefore, laser-induced membrane severing alone crosses the molecular irreversibility threshold, making it the sole biologically irreversible event in trophectoderm biopsy.

Given by Dr Charu Dutt Joshi