Oocyte Cryopreservation
Oocyte cryopreservation allows the preservation of fertility in women who wish to postpone motherhood, through a rapid freezing technique – oocyte vitrification.
After ovarian stimulation and follicular puncture, the collected oocytes are treated in the laboratory and cryopreserved for future use.
This procedure is indicated for women with oncological or non-oncological diseases, who are not advised to become pregnant at the moment and whose fertility may be compromised in the future.
Oocyte cryopreservation is also an option for healthy women who wish to postpone motherhood for any reason.
About Oocyte Cryopreservation
Oocyte cryopreservation is indicated for women with oncological diseases or other diseases that require treatments that may affect their future fertility, such as chemotherapy. In the case of women with oncological diseases, it is important to assess the time available until the start of chemotherapy treatment and obtain the assessment and agreement of the oncologist.
This technique is also recommended for healthy women who, for personal and/or professional reasons, wish to postpone their plans for motherhood until later in life, thus offering the possibility of preserving their reproductive potential.
The oocyte cryopreservation process involves several steps, starting with a medical consultation and definition of the protocol to be used, moving on to ovarian stimulation with subsequent follicular puncture and laboratory treatment of the collected oocytes, culminating in their cryopreservation.
Medical consultation
The patient is assessed using hormonal tests and analyses and the ovarian stimulation protocol to be followed is defined;
Ovarian stimulation
On the 2nd or 3rd day of the menstrual cycle, hormonal medication is started to encourage the recruitment and growth of several follicles at the same time. Regular ultrasound monitoring is performed to check the number and size of the growing follicles. Once the optimal follicular size has been reached, medication is scheduled to trigger the final maturation of the oocytes contained in the follicles. Follicular puncture is performed 36 hours after the administration of this medication;
Follicular puncture
Quick surgical procedure, performed under sedation and via the vagina, during which the fluid from each follicle is aspirated;
Oocyte selection
The follicular fluid obtained is observed in the laboratory and the oocytes are collected. These are evaluated for their degree of maturity and only mature oocytes are selected for cryopreservation;
Vitrification
The selected oocytes are cryopreserved in devices called straws, using the vitrification technique. The straws are stored in liquid nitrogen containers, where they remain until they are used.
In the past, oocyte cryopreservation was performed using slow freezing techniques which, due to the cellular specificity of oocytes, offered very few guarantees and lower than expected oocyte survival rates. The development of the vitrification technique, an ultra-fast freezing method, has allowed for a major advance in the cryopreservation of female gametes.
Vitrification allows the water, which is present in large quantities in the oocyte, to be replaced by cryoprotective solutions. This replacement protects the oocyte membranes and prevents the formation of ice crystals inside them, which would cause cell death. The oocyte is thus prepared to withstand the low temperatures to which it will be subjected, since the next step will be to cool the oocytes very quickly to temperatures of -80 ° C and store them in liquid nitrogen containers (-196 ° C).
The survival rate of oocytes after vitrification is above 90%. However, there are factors that will influence the use of these cryopreserved oocytes, namely oocyte quality.
In other words, oocytes that have been cryopreserved have a high probability of survival, but if their quality is altered, their use, i.e. fertilization and subsequent embryonic development, may be compromised.
Therefore, it is important to note that the success rate of oocyte cryopreservation is high but that the final objective – pregnancy – will depend on many other conditions.
The quality of oocytes is affected by several factors, the most important being the patient’s age. We can say that the later the oocyte cryopreservation is performed, the lower the quantity and quality of the oocytes recovered.
We should also bear in mind that cryopreservation of oocytes is never a guarantee of future pregnancy. Therefore, postponing motherhood should be discussed with your doctor to understand the risks involved.
When the time comes to use the cryopreserved oocytes, they will be thawed and fertilized using Intracytoplasmic Sperm Microinjection (ICSI). The embryos obtained will be kept in culture for 3 to 5 days and then the best quality will be transferred to the uterus.
Frequently Asked Questions
A woman’s reproductive potential begins to decline from the age of 35 and drops sharply from the age of 40. This means that the quantity and quality of oocytes decreases, which may compromise the success of the cryopreservation technique and subsequent fertilization of the oocytes. Therefore, the timing of oocyte cryopreservation should be discussed on a case-by-case basis with your doctor, bearing in mind that the later it is performed, the lower the chances of success.
According to current Portuguese law, oocytes can remain cryopreserved for a period of 5 years, after which the patient will have to sign a new consent to maintain cryopreservation for a new period of 5 years.
No Medically Assisted Reproduction technique can guarantee pregnancy. Oocyte cryopreservation only serves as a reserve of female gametes for future use, and the success of the technique cannot be guaranteed.
Follicular puncture is a surgical procedure, although minimally invasive, which requires sedation, so it is recommended that you rest on the day of the procedure and avoid physical exertion in the following days.
After completing the laboratory procedure, you will be informed of how many oocytes were cryopreserved and a medical appointment will be scheduled to discuss the need to repeat the procedure to increase the reserve of cryopreserved oocytes.
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