If we compare the pregnancy rate of treatments with egg donation with fresh or frozen eggs, we can observe that they are very similar.

Once the eggs have been joined with the sperm by microinjection, the development is very similar, regardless of whether they are fresh or frozen eggs. We spoke to Dr Llanos Medrano, senior embryologist at the international clinic for assisted reproduction IVF-Life Alicante, to answer these questions…

The world of assisted reproduction is constantly evolving, with new studies being conducted every day to help patients discover the reason for their infertility and how they can achieve their dream of conceiving a healthy baby.

In many cases, the only option for couples is to resort to treatment by donation. Requiring egg or sperm donation, or even embryo adoption raises questions about the selection of the gametes and whether vitrification worsens their original quality.

In the following article, our expert will explain the difference between fertilising fresh or frozen eggs and what the cryopreservation technique, according to Dr Medrano, a safe and effective technique that has become routine in our laboratories, involves.

What exactly does egg vitrification consist of?

Cryopreservation consists of freezing gametes or embryos using a medium that increases the viscosity of the sample until it becomes almost solid, thus avoiding the formation of ice crystals, which are very harmful to the cells. The vitrification of oocytes or embryos is carried out at a temperature of -196º C, managing to halt the time and therefore the age of the embryos until the moment of implantation.

At IVF-Life, we routinely use the vitrification technique for the oocytes of those patients who undergo social freezing or for surplus donor oocytes. We first prepare the oocyte for vitrification (denudation process) and then cryopreserve them using a media with special characteristics that stop the cellular activity and preserve them for future use.

“Using oocyte denudation, we prepare the egg for either vitrification or fertilisation by ICSI. It consists of using an enzyme and a mechanical process that eliminates the cells that accompany the oocyte.”

Dr Llanos Medrano, senior embryologist at IVF-Life Alicante.

Does the use of this technique affect the next steps in the fertility treatment?

Although the oocyte is preserved, the use of this technique results in the destruction of the cells that accompany the oocyte (granulosa) and therefore prevents the oocyte and sperm from recognising each other naturally, making conventional in vitro fertilisation (IVF) impossible.

This is why after vitrification, the egg can only be fertilised by sperm microinjection or also known as ICSI.

Fresh eggs, on the other hand, can also be fertilised through IVF, thus allowing nature to decide which sperm should combine with the egg.

What is the difference between fresh and frozen eggs?

As we already mentioned, the vitrification process does not affect the quality of the egg in any significant way. If we want to distinguish the main difference between a fresh egg and a vitrified egg, we have to focus on the viability of the egg itself. In other words, the main difference between a fresh egg and a frozen egg is the initial selection process.

When a couple decides to undergo fertility treatment using donated eggs, they can either be fresh or frozen; if they decide on using fresh eggs, the donor will then undergo ovarian stimulation in order to produce an adequate number of eggs to donate to the recipient couple.

On many occasions, there is a high response from the donor, generating surplus eggs, which end up being vitrified. In our laboratories we have a survival rate of around 89%, thanks to the most advanced technology and the knowledge of our staff, we ensure that we obtain the best reproductive outcome.

Do fresh eggs guarantee higher pregnancy rates

The concept of vitrification and subsequent devitrification of frozen eggs and embryos has changed dramatically in recent years thanks to advances in freezing techniques.

Based on studies conducted and data collected by our fertility clinic during the year of 2021, we can confidently deny that fresh oocytes guarantee higher pregnancy rates. It has been shown that in vitro fertilization rates, embryo division and embryo quality are not affected by vitrification. Pregnancy rates and live newborn rates are also not significantly different.

“Thanks to the research in the laboratory, we have been able to achieve similar implantation or pregnancy rates for embryos obtained from fresh and frozen eggs,”

Dr. Llanos Medrano

 

Is there a difference in the blastocyst formation of a devitrified and a fresh oocyte? 

Fact is that the rates are very similar and transferring embryos obtained from fresh or frozen eggs does not affect the implantation or pregnancy rate. However, there is a difference of 8% among the embryos that make it to the blastocyst stage. Why is that?

On the one hand, one of the possible factors causing this discrepancy may be the fact that by using fresh eggs we avoid artificial processes such as vitrification of oocytes or embryos and their subsequent thawing. It is true that any artificial interference in the process will reduce the chances of success of the fertility treatment, even if only minimally.

On the other hand, but no less important, when using fresh eggs the embryologist makes sure to choose the best eggs. Whereas when using vitrified eggs they may not have the same quality and viability as they stem from remaining eggs that were not initially selected for the fresh transfer.

Therefore, if the egg donation treatment is performed with vitrified eggs, it is necessary that these are devitrified first. This implies that some eggs may be lost during the process. To avoid compromising the performance of the cycle, the number of vitrified eggs given to patients is somewhat higher than that given to patients with fresh cycles.

It is therefore essential that when working with vitrified oocytes, the laboratory maintains very high survival rates.

Fresh eggs and vitrified sperm

At IVF-Life we work with fresh oocytes, meaning that we only stimulate the donor once she has been matched with a suitable patient.

When choosing which vitrified gamete to use, we generally prefer using fresh oocytes and cryopreserved sperm. The survival rate of a vitrified oocyte, although very high, is not 100%. For this reason, we always prefer to start with fresh eggs.

This is not the case with semen, as our specialist explains:

“It is true that devitrification may minimally reduce the number of oocytes that have been frozen. However, with sperm it is different. There are millions to choose from. It is also a way to improve the comfort of the couple, as they will not have to return to the clinic to submit their sperm sample, but rather the day they return will already be the day of the embryo transfer. Additionally, this embryo can be frozen, as the survival and pregnancy rates are no different from that of a fresh transfer”.

In conclusion, the use of vitrified donor eggs for assisted reproduction is a safe process. It allows similar results to those obtained with fresh oocytes. However, this technique should only be used in cases in which the quality and viability of the eggs are guaranteed in order to generate viable embryos and, therefore, the birth of healthy babies.

If you have any doubts or find yourself in a particular circumstance, please feel free to contact us through this form or, if you prefer, make an online or face-to-face appointment with us. Remember that every month we offer individual consultations with one of our IVF-Life specialists.

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