ембриолог на болница "Надежда" подготвя яйцеклетки за замразяване

reproductive medicine

Egg freezing

If you do not feel ready to become a mother for various reasons yet, egg freezing could be your chance to preserve your fertility for the future moment you choose to embark on your reproductive plans. This way, when you decide to do it, your chances of getting pregnant will be equal to those you had at the time you froze your eggs.


Why freeze eggs?

Women often wrongly think that egg freezing is done only before cancer treatment or as a part of IVF treatment. Another myth is that egg freezing is only done in women over 40. Oocyte cryopreservation is, in fact, an appropriate and justifiable solution for women in various life situations who have one major thing in common – their wish to be mothers (again) in the future.


Through the ‘Keep Hope Alive’ project, Nadezhda Hospital is actively engaged in fertility preservation for cancer patients and patients with autoimmune and rheumatoid diseases.

Before you start preparing for egg freezing, though, make sure you do the following:

Egg freezing step by step

Depending on your reasons for egg freezing and the specific workflows at different clinics, the steps described below might vary. Nevertheless, there are typically four main stages you will go through:

  • Preliminary tests and consultations – to assess whether the procedure is feasible in your case and to check for contraindications, as well as plan the second stage;
  • Hormonal stimulation of the ovaries – usually, one egg matures each month in one of the ovaries. When you have to collect enough eggs for freezing, though, the ovaries are stimulated by hormonal medication so that they can grow not one but five, ten, or fifteen oocytes at once.
  • Egg retrieval – the oocytes have to be collected when they have matured, just before their follicles pop. This is done by a minimally invasive procedure – follicular aspiration.
  • Freezing of good quality eggs and finalizing long-term storage paperwork.

NB! Do your due diligence about every step of the process you are about to start.

The procedure will take up a little bit of your time. Nevertheless, you need to plan your tasks carefully and make room for the frequent check-ups you will have at the reproductive clinic over one or two weeks.

If you have already made your informed decision to freeze eggs for future use, continue by booking your appointment for a consultation with a fertility specialist.

First and foremost, your ovarian reserve must be evaluated to make forecasts for the procedure results. Ovarian reserve assessment includes an ultrasound scan by a qualified expert to determine the ovarian size and antral follicle count and blood tests of four key reproductive hormones, which are considered relevant ovarian reserve indicators. These are the follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (Е2) and Anti-mullerian hormone (AMH). These tests can be done in advance, but please keep in mind that you have to visit the lab on day two or three of your period for the results to be correct.

On the day of your appointment with your fertility consultant, bring all your tests and documents from any previous treatment you might have had. Do inquire about your family medical history in advance. Inform your doctor about any chronic or past disease, as well as conditions that run in the family. You have to inform them if you are taking any medication currently, including contraceptives and food supplements.

Prepare to share details about your menstrual cycle: what is its duration and at what periods, is your flow heavy, has it skipped a month, do you suffer from strong pain or irregular bleeding. Draft the key questions before you enter the doctor’s office. Ask about the side effects and possible risks of the procedure. Remember, there are no dumb or inappropriate questions. Feel free to ask about anything you want to know.

Since the procedure involves ovarian stimulation and an invasive manipulation under short sedation (oocyte retrieval), this is the stage when your doctor should investigate your complete medical history and make a conclusion confirming you have no contraindications to proceed. If necessary, you may be assigned additional consultations with an internal diseases specialist, an endocrinologist, a cardiologist, or other medical specialists, depending on whether you have any concomitant diseases and what they are.

The process starts with a check-up of your current gynaecological status in the present cycle. This includes an ultrasound examination and blood tests of serum levels of the reproductive hormones (LH, FSH, E2) on day two or three of your period. If necessary, additional hormones may be tested (TSH, FT4, prolactin).

You will receive documents detailing information about the upcoming procedure to acquaint yourself with it before ovarian stimulation starts.

To collect a sufficient number of eggs in one cycle, the ovaries have to be stimulated by low-dosed synthetic (purified) hormonal medication. These are prescribed by your doctor and are applied following a protocol – most often including subcutaneous injections in the course of 10 to 13 days.

Modern reproductive medicine has a large repertoire of medications available, from which the most suitable for you and your ovaries will be chosen. Some are in the form of pills, some are injections applied as single shots with prolonged action over several days. Your fertility consultant will decide which medication is the best for you and what treatment protocol to be used, taking into account your test results and your ovarian response to the ongoing stimulation.

The stimulation process is closely monitored by your fertility team through blood hormone levels and ultrasound scans (typically every other day). Strict monitoring aims to guarantee the procedure’s normal progress and ensure any side effects or adverse events are identified and assessed. Moreover, your doctor needs to follow up on the ovarian response to stimulation to precisely determine follicle growth and schedule the oocyte retrieval or the egg collection procedure.

The moment of truth! Now that the hormonal stimulation has played its part, there are many follicles of sufficient size that your doctor will aspirate to collect the eggs inside.

A special needle guided by an ultrasound probe is introduced through the wall of the vagina to access the ovary. The fluid filling the follicles and containing the eggs is aspirated and handed over to the embryologist, who inspects it immediately under the microscope to check for the eggs. The embryologist then washes the eggs and transfers them to a specially formulated medium to keep them safe from environmental stress. A key detail: it is only now that both your doctor and you will get to know how many of the follicles you have been watching grow in the course of stimulation do actually contain mature eggs inside. The number of eggs retrieved does not always match the number expected from the follicle count. You will be told the final egg count after the oocyte retrieval is complete, and it will be included in the medical report that you will receive after the procedure.

Egg retrieval typically lasts for about 5–10 mins. It is performed under short sedation, and you will stay under monitoring in the clinic for about two to four hours. You will not be able to go to work on that day, and we recommend that you abstain from driving too. It is best to have a friend or relative take you home after the procedure. Typically egg retrieval goes smooth and without complications, so you can go back to work right on the next day. If your job involves physical strain, though, we recommend that you take several days off work, for which you can receive a sick leave document from the hospital.

For many ladies, egg retrieval is the scariest part of the whole egg freezing process. Although minimally invasive, it is not entirely devoid of risks, about which you have to inform yourself and discuss with your doctor.

Up to this moment, you would have followed the typical stages of a standard IVF procedure. From this point onwards, you will be taking a different path.

In couples undergoing an IVF cycle, the procedure typically goes on with the in vitro fertilization of the collected eggs, then culturing of the resulting embryos in the lab, and preparation for placing them back into the woman’s uterus (the so-called embryo transfer).

Fo you, however, the procedure stops at this stage – for now at least. The eggs will be evaluated by a qualified embryologist and then frozen.

After the eggs have been frozen, they go into the care of the experienced biologists in our cryobank, who continually monitor the storage conditions to guarantee the quality cryopreservation of your gametes.

You will sign a contract for egg cryopreservation and storage, which specifies all the conditions of freezing and the period of storage of part or all of the viable genetic material, the rights and obligations of the parties, the methods of payment and termination of the contract. After the expiry of the contract, if you so wish, it may be extended by signing an annex. If you require any assistance or further information, please contact tel. 0887 701 927.



In accordance with Regulation No. H-2 of 12 July 2023 on assisted reproduction activities of the Ministry of Health

Art. 71. Good reasons for the withdrawal and destruction of ova, spermatozoa and zygotes are:


1. the written certified wish of the patients;


2. the expiry of the maximum storage period requested by the patients when signing the declaration of informed consent prior to cryopreservation;


3. the risk of cross-contamination or transmission of bacterial or mycotic infection;


4. the risk of cross-contamination or transmission of a transmissible disease (HIV, hepatitis B and C, syphilis, etc.);


5. the expiry of more than 6 months after the requested storage period for unclaimed sperm, ova or zygotes;


6. the death of the spouse/partner, irrespective of the existence of a declared wish during his/her lifetime, in respect of spermatozoa or zygotes, except in the cases referred to in paragraph 5.9 of Section IV of Annex 1 to Art. 1, т. 1;


7. the death of the spouse/partner, notwithstanding the existence of a declared wish during lifetime, in respect of oocytes or zygotes;


8. the establishment of a disease in an anonymous donor which can be transmitted to the offspring or the recipient;


9. the impossibility of securely identifying donors or tracing the path of genetic material due to incorrect or missing labelling or confusion during processing.

Egg freezing for social reasons

Below are some social reasons to consider egg freezing as an option for female fertility preservation:

  • If your relationship has not evolved yet or your partner does not feel ready for you to become parents;
  • If you have not met the partner yet who you would like to be the father of your children;
  • If you are facing crucial steps in your academic or career development;
  • If you are a mother already and you would like to hаve more children, but for various reasons, you’d prefer to do this at a later moment in the future;
  • If you still have not completed your list of summits to conquer before making a nest.
  • If you are undergoing IVF treatments but embryo freezing is unacceptable for you on religious or ethical grounds.

Cancer and fertility preservation

When faced with this terrifying diagnosis, the first concern of our doctors and family is that we start proper treatment as soon as possible


In this challenging moment we do not always have enough information and clarity about all aspects of the forthcoming cancer treatment and its side effects. We all know that we could lose our hair for some time, but not all of us know that together with our hair, we could lose our chances to have babies. The powerful drugs used to fight cancer cells could deal a fatal blow to the gentle structures of the ovaries or testes. Ionizing radiation used in radiotherapy can have the same deleterious effects on our reproductive organs.


You might say, who would be thinking about getting pregnant and having babies when they are facing cancer! But when we sit and check all the things we have to sacrifice to fight cancer, though, the thought that we could possibly never have our own child could rob us of the last drops of courage.

Above all you need to know that not every cancer therapy causes inadvertent harm to fertility. When there is a known risk, though, medicine can help you save your chances for parenthood after cancer.


This is possible through the modern methods of assisted reproduction. They make possible the collection and long term storage of your genetic material until the day your oncologists confirm that you are healthy and can go on planning pregnancy and birth.

While in men and boys the collection and cryopreservation of their genetic material is a simple, easy and relatively cheap procedure, the collection of mature eggs from the ovaries is a bit more complex, and the procedure can only be started after a precise assessment of your reproductive status and a consultation with your cancer therapist. When the patient is in a relationship, the couple can decide to freeze not eggs but embryos (after undergoing in vitro fertilization).


The sperm, eggs or embryos collected are frozen using special methods and are stored in the cryobank under ultra-low temperatures that guarantee their viability will be preserved for years.


Depending on how soon you need to start your cancer treatment and whether your specific type of cancer is sensitive to the activity of the sex hormones in your body, there are different options for ovarian stimulation to produce a larger number of eggs.


Each patient is assessed on a case-by-case basis, and all relevant medical detail is evaluated by an interdisciplinary committee on which consultants in reproductive medicine and oncology sit. Nadezhda hospital has a standing committee on fertility preservation in cancer patients.


Whether a fertility preservation procedure would be feasible depends entirely on the individual medical details of each case and the best interest of the patient – cancer treatment is life-saving, and while there are cases when it can be safely postponed to accommodate fertility preservation, sometimes it cannot be delayed even for a week!


The primary goal of cancer treatment is saving your life and recovering your health and wellbeing, and it is your oncologist’s decision to find the best option for you. If our fertility specialists have a safe window and zone of action to preserve your chances to have your offspring, we will do anything. But we will never allow you to postpone or reject the cancer treatment for the sake of fertility preservation – there are various ways in which you can become a parent, and we will support you in finding yours!

ембриолог на "Надежда" се подготвя да извърши класическо инвитро оплождане

What is egg freezing?

When living cells are cooled down below a certain temperature threshold, their metabolic processes are put on hold, and the clock stops ticking. They could theoretically spend months, years, and decades in such a state of deep hibernation. The temperature threshold that must be crossed to make this possible is –130°C, colder than the coldest spot on earth. The only way to achieve it is by using liquid gas – in our case, liquid nitrogen. The sample is prepared for freezing by adding one or more cryoprotectants, chemicals used to prevent cryogenic damage to cellular structures during freezing.

Does egg freezing require a special technology

The oocyte is indeed very special. It is the largest cell in the human body and has an extremely high content of free water molecules. Here lies the big trouble – as we know, water is the only substance that increases its volume instead of shrinking when cooled down between 4 and 0 degrees Centigrade. When water freezes, it forms gorgeous but deadly crystals – they literally cut living cells into pieces. That is why ice crystal formation is something we try to avoid at all costs when freezing living cells.

You may have read that egg freezing is a brand new, experimental technique with no proven efficacy. Fact-checking proves different. The first attempts at egg freezing date many years back, pioneered by Dr Christopher Chan in Australia, who reported the first birth after such a procedure in 1986. It took scientists three more decades to develop an effective method for human oocyte cryopreservation.

The long-awaited success in egg freezing came with the invention of a new method, the so-called vitrification. It uses high concentrations of cryoprotectants and ultra-rapid cooling rates. In this way, detrimental ice formation is avoided, and the free water inside the cells transitions directly into a glass-like state. The technique was named vitrification after the Latin word for glass, “vitro”.

The first reports of procedures using vitrified eggs surpass all expectations: over 95 % of oocytes were viable after thawing, 90% of those were successfully fertilized and developed into viable embryos; the resulting clinical pregnancies were more than 65%. Albeit slowly at first, vitrification was introduced in clinical practice worldwide and is today a routine technique in most centres.

In 2012, following an in-depth literature review of hundreds of research publications, the American Society of Reproductive Medicine (ASRM), one of the most influential expert organizations in assisted reproduction, issued an official opinion statement in which oocyte freezing by vitrification was announced a medical technique of completely proven efficacy and safety.

Even today, freezing the female gamete remains a challenge. Vitrification has to be performed by specially trained embryologist technicians to be successful. And then, for eggs to preserve their quality intact while frozen, their storage conditions have to be under continuous monitoring, which requires extra effort and resources by the clinic.

See also

Fertility preservation
Sperm freezing
"Keep Hope Alive"
The cryobank of Nadezhda hospital