Is it better to freeze eggs or embryos?

State-of-the-art assisted reproductive technologies actively use cryopreservation methods to treat and overcome infertility. With the help of cryopreservation, it is possible to freeze both germ cells (spermatozoa and eggs) and embryos. But what is better to choose?

What do you mean by cryopreservation?

This is a technology in which cells are deeply frozen and stored in liquid nitrogen at very low temperatures (-196 degrees). Modern technologies make it possible to freeze cells instantly (at a speed of 20,000 degrees per second), preventing the formation of ice crystals inside them and protecting against death during thawing. In this state, all biological processes in cells stop, enabling them to be stored for an indefinitely long period.

What is better to freeze?

There is no single answer to this question. It all depends on your ultimate goal.

Egg freezing may be needed:

• in the "Delayed motherhood" programme
• with reduced ovarian reserve
• before upcoming radiation or chemotherapy
• for egg donation
• in oocyte banking programmes.
• Embryo freezing is relevant:
• for subsequent IVF attempts
• for preimplantation genetic testing of the embryo
• if, for some reason, the transfer cannot be carried out in the same cycle.

To conduct IVF, it is better to cryopreserve embryos since, for the onset of pregnancy, the protocol will require thawing only 1–2 embryos but 6–8 eggs at once (this is the minimum number).

If we talk about freezing–thawing process, there are some nuances here. Embryos tolerate it well, and cryopreservation does not affect the subsequent pregnancy and the unborn baby’s health. But the eggs are a little worse. When the eggs are thawed, about 20–30% of the cells are damaged and unsuitable for further use in ART programmes.