Embryologists are meticulous about culture media. Obsessive about incubator CO2 levels. Rigorous about vitrification technique. But there’s one step in almost every ICSI cycle that gets surprisingly little formal scrutiny, oocyte denudation.

Denudation is the process of removing the cumulus and corona radiata cells surrounding a mature egg before ICSI. It’s done with a fine pipette, usually after brief hyaluronidase treatment, and it takes maybe two minutes. It’s also one of the most mechanically delicate things an embryologist does.

The meiotic spindle, the structure that controls chromosome segregation is invisible under standard light microscopy and extremely sensitive to mechanical disruption. Aggressive pipetting technique during denudation can displace it. That displacement can cause fertilisation failure or chromosomal errors that only show up days later, at blastocyst stage or in PGT-A results, with no obvious trail back to what happened during those two minutes at the denuding dish.

What’s interesting is that labs which have gone back and formally audited their denudation protocols standardising timing, pipette sizing sequences, and hyaluronidase exposure duration have generally found improvements in fertilisation rates. Which suggests there’s meaningful room for optimisation in a step most labs consider already sorted.

Worth thinking about. More at www.cryolab.co.uk