Have you ever wondered what happens with the semen samples, oocytes or resulting embryos after an assisted reproduction treatment? We explain to you what vitrification involves and for what purposes it is used in assisted reproduction.

What is vitrification and what it is indicated for

Vitrification is a technique by which tissues or cells are frozen in order to be used in the future. In assisted reproduction this technique is used to freeze and store viable sperm samples, eggs and embryos that were not used in the initial fresh eggs transfer, that is, in in vitro fertilisation.

Vitrification is used to preserve these samples so that they can be used in the future, either by the patient herself or the couple themselves, or so that they can be donated. In other words, the resulting embryos after an in vitro fertilisation cycle can be stored in case the patient wishes to become pregnant in the future, be donated to other women or couples, or they can be donated for research. Vitrification is used to guarantee the appropriate preservation of these embryos.

It is an ultra-fast freezing technique that substituted slow freezing used before.  Survival rates have increased since the introduction of vitrification and higher pregnancy rates have been achieved in frozen embryos transfer.

Vitrification in assisted reproduction

Are you curious and you would like to know how this works? A cell is frozen in a solid similar to glass but which is free of any crystal formations.  In order to avoid these ice crystals forming, a cryoprotectant is used. This is very important in embryology because ice crystals can damage the frozen cells or embryos, which thanks to this technique will not happen.

Embryos can be frozen in the pro nuclear phase (when they are a single cell) or in any other later phase. Generally, embryos are vitrified in the blastocyst stage – that is, on day five after fertilisation.