reproductive medicine

Sperm freezing

If you are not ready to become a father today for various reasons or do not have immediate plans for parenthood, but you are concerned about your sperm parameters declining,  a fertility preservation option is to freeze your sperm. When the time comes for you to embark on your path to parenthood,  you will have better quality reproductive material securely stored beyond the adverse impacts of ageing, so your chances will be better.


Why freeze sperm?

Most men typically are able to have children even with advancing age,  as opposed to women whose fertility declines as they close menopause. What is not largely known is that nowadays, men too suffer a decline in sperm quality with age. Unfortunately, this process has been accelerating due to lifestyle, environment, alcohol and substance abuse, smoking, excess exposure to heat or chemicals, pesticides in food, etc. A possible solution in such cases is to freeze sperm before damage to sperm parameters has become inadvertent.


Male fertility decline starts around the age of 35, with a decrease in testosterone and worsening of sperm quality, and progresses with age. Taking into account the trend for delaying parenthood to a later age, and the increasing number of divorces and second marriages, it is recommended that a prophylactic semen analysis is done once a year. Fertility preservation options can be discussed if any abnormalities or signs of deteriorating sperm quality and quantity are found.


There is a current trend in the USA for men to freeze sperm at a younger age to have better chances for parenthood later. Behind this decision lies the desire to overcome the negative impact of ageing and other factors that could affect the quality and quantity of sperm.


Currently, men in Bulgaria choose to freeze sperm too, but primarily for medical reasons – for example, before undergoing cancer treatment with a high risk for their fertility or if they have been diagnosed with a disease whose progression inadvertently affects fertility, like some autoimmune and rheumatoid diseases. Upcoming surgery of the prostate or the testes is another reason to freeze sperm.


Through the ‘Keep Hope Alive’ Project, Nadezhda Hospital actively engages with male and female fertility preservation for cancer patients and patients with autoimmune or rheumatoid disease.

Risk factors

For many men, the very choice of their profession could predetermine a high fertility risk. Such high-risk occupations include:

  • Culinary occupations, where exposure to excessive heat can cause sperm defects. It is with a purpose that the testes are located outside the body – sperm feel best at lower temperatures, typically between 25°C and 35°C. Prolonged exposure of the testes to higher temperatures can severely impact spermatogenesis.
  • Occupations related to exposure to toxic substances like paints, to radiation and other environmental risks.
  • Sedentary occupations involving a forced posture for prolonged periods, such as international truck drivers. Keeping the thighs together raises the temperature of the testes, which puts spermatogenesis at risk.

Smokers’ semen analysis results are 13-17% worse than non-smokers. In men who quit, sperm counts are increased by 50-80% after smoking cessation.

Pesticides pose a significant risk for male fertility as they mimic the presence of estrogen in the body and negatively impact sex hormonal balance. Herbicides and pesticides can cause an elevation in female sex hormones in the male body, which results in poor sperm parameters

High body concentrations of lead impair fertility and can cause erectile dysfunction.

Some artificial substances added during the production of  meat and dairy are hormones that act similar to estrogen when they get in the body, and they increase men’s risk of infertility.

Research has shown that in men with poor semen quality, excess alcohol use is a cause of lower sperm counts.

When heated, plastic products release xenohormones (chemical hormones), which mimic estrogen in the body. Elevated levels of estrogens correlate to an increased risk of infertility.

Sperm are stored in the testes at temperatures lower than the rest of the body. Therefore, heat is one of the risk factors with the most pronounced negative effect on sperm. It is recommended to avoid saunas and hot tubs because they raise the temperature of the testes too much.

A diet poor or deficient in vitamin C, selenium and zinc results in deteriorating sperm parameters.

Contemporary life’s daily stress is a significant contributor to the excess production of free radicals.

Obesity negatively affects semen parameters. It is no secret that fat tissue releases hormones and, in this way, negatively affects spermatozoa.

Anabolic steroids impair sperm production and cause shrinking of testicular tissue.

Substance abuse– cocaine and marijuana (weed, cannabis) decrease sperm counts and  sperm quality.

The fertilization potential of sperm gradually declines after 35. A deterioration of semen parameters is observed in most men, though some retain perfect fertility well into their 70s.

Sperm freezing step by step

Sperm freezing is a well-established method for male fertility preservation. It is a routine procedure for any man of reproductive age, irrespective of whether he has immediate plans for parenthood. It is quick and requires no hormonal pre-treatment. In cases of poor semen parameters, several rounds 2-3 days apart are recommended. When spontaneous ejaculation is impossible, invasive surgical procedures can be applied, such as testicular sperm extraction (TESE).

If you want to start a sperm freezing procedure, you first need to book an appointment for an andrologist consultation, where you will discuss if any additional tests are required. After this, a standard semen analysis is done  – this is a routine test to determine the main physical and chemical characteristics of semen, sperm count, sperm motility and outer appearance (morphology). At the discretion of your doctor and the andrologist, additional tests can be assigned (advanced semen analysis, microbiology, virology test etc.). The number of rounds needed to complete the sperm freezing cycle is decided on a case by case basis, depending on semen analysis results and the individual needs.

Semen is collected in sterile containers by masturbation in dedicated collection rooms and is then handed over to a biologist from the Andrology lab. At Nadezhda hospital, collection rooms are located immediately next to the Andrology lab and are connected with it. After processing and purification, sperm are divided into several aliquots in separate cryovials. This helps avoid multiple freeze-thaw repetitions in the future and lowers the risk of impaired sperm viability.


NB! In patients with viral and/or bacterial infections, antimicrobial treatment has to be assigned and completed before commencing the sperm freezing procedure, and additional advanced techniques for sperm purification might need to be applied. Every step of the process is discussed with the patient, taking into account their specific condition.

The modern method of sperm freezing applied at Nadezhda hospital is called vitrification, or ultrafast freezing. After the sperm have been washed and purified, they are placed in a special medium containing cryoprotectants. Freezing is done in cryovials which are immersed in liquid nitrogen. The cooling rate in this technique is many times faster than traditional methods, which helps reduce the cryogenic damage to cells from ice crystal formation, which is kept to a minimum. Cryovials are placed into special cryogenic tanks loaded with liquid nitrogen and are stored at ‑196°C.

To be successful, vitrification has to be performed by specially trained andrologists. For sperm quality to be preserved, critical storage conditions must be continuously monitored. Our cryo tanks are fitted with a fully automated system for liquid nitrogen supply as well as with sensors for temperature monitoring and control. In this way, the required temperature conditions can be sustained for indefinitely long periods.

If you are having your sperm frozen, you will sign a contract for 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.

The process of thawing sperm takes about 60 minutes. Next comes a purification step, followed by sperm viability and motility tests. If a sufficient number of rapid, progressively motile sperm is observed, no additional processing and selection are necessary, and they can be directly used for fertilization of eggs in the IVF cycle planned.

See also

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