Vitrificación de óvulosVitrificación de óvulos

Egg vitrification

Técnica destinada a preservar los óvulos a través de una congelación ultrarrápida. Los óvulos pueden congelarse por el tiempo que la paciente lo necesite.

What is egg vitrification?

Vitrification is currently the most effective technique for preserving eggs. This is an ultra-fast freezing technique in which the cooling rate is so high that the liquid water inside the cell, instead of turning into ice (as occurs in slow freezing), passes directly into a glassy state. Intracellular ice crystals often cause irreparable damage to the egg, so preventing ice formation is key to the subsequent survival of the eggs and the greatest advantage of vitrification.

The process of obtaining eggs for vitrification is the same as for an in vitro fertilisation cycle: ovarian stimulation is carried out using hormones, followed by the retrieval of oocytes through ovarian puncture. Oocytes are classified according to their maturity, and it is the mature oocytes that are vitrified.


Stages for obtaining eggs

1 - Ovulation stimulation

In the first stage, the woman undergoes hormonal stimulation of the ovaries to achieve oocyte maturation. In this case, we have different ovulation stimulation protocols that must be applied depending on the cause of infertility, the patient's hormonal profile and age. Likewise, the dosage of the drugs is also adjusted to each patient's individual profile.

In most cases, the treatment is administered in the form of injections that are given subcutaneously by the patient herself. During the ovulation stimulation process, ultrasound scans and blood tests are carried out to monitor the cycle and ensure a good response in terms of the quantity and quality of the eggs we are going to obtain. This stage usually lasts an estimated 15 days.

Ovulation-stimulating medication has no significant side effects for the patient. Even so, you may experience fluid retention and/or mild abdominal discomfort. In relation to the risks associated with ovulation stimulation, it is important to consider ovarian hyperstimulation.


2 - Ultrasound-guided ovarian puncture

Once the eggs have matured in the ovaries, they are extracted to be fertilised in the laboratory. This is carried out through an ultrasound-guided follicular puncture.

The puncture is performed under sedation and is painless. It is performed in a surgical area, with the collaboration of the gynaecologist who performs it, an anaesthetist, a nurse, and the biologists who will collect the oocytes. The oocytes are aspirated from the ovaries and transported to the laboratory in their own follicular fluid. Mature oocytes are vitrified in the laboratory.

The follicular puncture takes approximately 20 minutes. After the puncture, the patient remains for a while to recover from the anaesthetic and can then go home, where she is advised to rest for the rest of the day.

In which cases is egg vitrification indicated?

Egg vitrification is mainly indicated in:

Women who must undergo medical treatments that may affect ovarian function:

  • Young cancer patients who are going to undergo chemotherapy and/or radiotherapy
  • Young patients who are going to undergo surgery involving significant loss of ovarian tissue, such as in severe endometriosis.
  • Women who wish to postpone motherhood
  • Couples who, for ethical reasons, do not wish to freeze their embryos
  • IVF cycles with low ovarian response with the aim of accumulating oocytes
  • IVF cycles in which, on the day of ovarian puncture, the male partner is unable to provide a semen sample to fertilise his partner's oocytes.

To what extent does it guarantee successful fertilisation?

Oocyte vitrification achieves high survival rates, between 80% and 95%, depending on the patient's age and the quality of the oocytes. Vitrified oocytes that survive thawing have characteristics very similar to those they had before being vitrified, which means that they can be fertilised and generate embryos just as they would if they had not been vitrified.

Can all women benefit from oocyte cryopreservation?

Most women can benefit from vitrification; however, it should be noted that the results of this technique depend directly on the quality of the vitrified oocyte. In this regard, there are two situations that are worth mentioning:

  • In women over 38 years of age, the results obtained are lower due to the decrease in the quality and quantity of oocytes with age.
  • In prepubescent girls who have not yet begun to ovulate, vitrification is not indicated as they do not produce oocytes that are suitable for vitrification.

For women who have had cancer, how does egg vitrification benefit them?

Cancer treatment to combat cancer results in a decrease in ovarian function, and even its complete elimination in many cases. This means that the ovary ages between 5 and 10 years, and therefore the quantity and quality of the oocytes is reduced. Faced with this situation, most patients will have to resort to more or less complex assisted reproduction techniques (insemination, in vitro fertilisation, egg donation) depending on the patient's age and ovarian reserve.

In this context, vitrification is particularly useful and beneficial prior to cancer treatment. At that point, the oocytes can be preserved in the best conditions and used in the future to attempt the desired pregnancy.

Can it be considered the best technique for preserving female fertility?

In addition to vitrification, there are other treatments to preserve fertility: ovarian tissue freezing, ovarian transposition, ovarian protection with GnRH agonists, and in vitro oocyte maturation.

Although these techniques are considered experimental and offer inferior results to vitrification, they may be the only option available for certain patients. For example, oocyte vitrification is not indicated in girls, and ovarian tissue freezing would be the technique of choice.

How long can vitrified eggs be stored?

Vitrified eggs, like embryos or other types of tissue, can remain frozen for as long as the patient needs, since technically, eggs do not deteriorate over time and legally, there is no time limit.

How does it differ from other techniques?

The main advantage of vitrification over other freezing techniques is the high survival rate of oocytes upon thawing and the maintenance of their ability to be fertilised at levels similar to those of fresh (unfrozen) oocytes.

In practice, this characteristic of vitrification allows women to have children years later with similar chances to those they had when the oocytes were vitrified.

The main drawback of vitrification, and of any other preservation technique, is the limited number of oocytes available.