Modern reproductive medicine is advancing rapidly, with new technologies and effective methods being developed to prevent infertility. This progress offers the possibility of experiencing the joy of parenthood after the age of 40, when natural fertility declines. Today, one of the techniques that enables conception, carrying, and giving birth to a healthy child is egg freezing.
What is oocyte cryopreservation
Oocyte cryopreservation, or egg freezing, is an effective and safe technology that involves the puncture of follicles, processing and assessment of oocytes, and their vitrification. This is achieved by rapidly lowering the temperature to extremely low levels using liquid nitrogen. This process halts all biological activities in the eggs, keeping them viable indefinitely. Once thawed, these oocytes can be used for artificial or in vitro fertilization (IVF). Thus, vitrification (rapid freezing) ensures maximum preservation of oocytes.
In 2000, the Human Fertilisation and Embryology Authority (HFEA) in the United Kingdom approved the use of frozen eggs as a safe method for treating infertility. In 2013, the American Society for Reproductive Medicine (ASRM) confirmed that oocyte cryopreservation is no longer considered an experimental technique.
The optimal age for cryopreservation is between 25 and 30 years. After age 35, the quality and quantity of female gametes change: quality declines and quantity decreases. Conceiving naturally or through IVF becomes significantly more challenging. According to 93.9% of women, concerns about age-related fertility decline influenced their decision to use egg freezing.
What you need to know about oocyte cryopreservation
When deciding on oocyte cryopreservation, consider the following points:
- Age at which you freeze your eggs: To assist women in deciding whether to undergo oocyte cryopreservation and the optimal timing, American researchers have developed a special forecasting model. This model shows that, for a 50%, 80%, and 95% probability of having a child using cryotechnology, a woman under 36 years old should freeze 6, 14, and 30 eggs, respectively. For women aged 36 and older, freezing 15 eggs gives a 50% probability, 33 eggs gives an 80% probability, and 70 eggs gives a 95% probability.
- Number of eggs to store: On average, the number of oocytes retrieved by puncture for women under 35 years old is 13, and for those aged 35-39 years, it is 10. According to the aforementioned model, women under 40 will need to undergo at least three hormonal cycles to achieve an 80% chance of having a child in the future.
- Number of cycles: According to a study on the effectiveness of using frozen eggs conducted in the USA, women under 35 years old needed to thaw 41 oocytes to conceive a child. For women aged 38-40 years, the number of thawed oocytes required was 99.
Indications for the procedure
The popularity of oocyte cryopreservation continues to rise. Women opt for egg freezing for a variety of reasons, both medical and social.
The most common indications for oocyte cryopreservation include:
- Genetic predisposition to early menopause.
- History of endometriosis.
- Planning conception after undergoing chemotherapy or radiation therapy for cancer, which negatively affects reproductive function.
- Cytostatic therapy for autoimmune diseases.
- Desire to postpone motherhood due to certain life circumstances (lack of a partner, both partners being unready for parenthood, career, education, concerns about giving birth during a risky time, etc.).
Today, more and more women choose oocyte cryopreservation due to social reasons. According to some epidemiological data, the majority of these patients are successful in their professional lives and financially independent. They aim to first achieve their ambitious goals and then use their frozen oocytes to conceive a child.
How oocyte cryopreservation works
The oocyte vitrification program takes approximately two weeks and involves several stages:
- Preparation of the woman’s body: Comprehensive medical examination by various specialists, including ultrasound and blood tests for monitoring (measuring hormone levels to determine the stage of folliculogenesis).
- Hormonal stimulation: A course of injections to stimulate folliculogenesis—maturation of multiple follicles with mature oocytes. The dosage is determined based on the patient’s age, weight, number of oocytes, and anti-Müllerian hormone (AMH) level.
- Aspiration: Retrieval of follicles containing mature oocytes through a transvaginal procedure under ultrasound guidance with short-term intravenous anesthesia. The procedure lasts 20–30 minutes.
- Cryopreservation of oocytes: Preparation of oocytes and transfer into liquid nitrogen. First, oocytes are evaluated for quality by embryologists and then undergo vitrification. The frozen material is placed in specially marked containers. Vitrified oocytes have an unlimited storage period, which does not affect the quality of the resulting embryos or the course of pregnancy.
- Recovery: After the procedure, the woman remains under medical supervision for about 2 hours. She may experience mild abdominal pain, spotting, or general weakness. After assessment by the reproductive specialist and anesthesiologist, the woman may go home.
The doctor will provide the patient with information on the number of frozen oocytes and further recommendations. Some women may need several cycles to accumulate a larger number of oocytes.
Once the decision is made to plan a pregnancy and use the cryopreserved oocytes, the patient should contact the clinic to plan the cryopreservation protocol. Before the program, an examination of the couple is conducted. If there is no partner, the woman may use donor sperm.
On the scheduled day, all or some of the oocytes will be thawed and fertilized with the partner’s sperm using ICSI (Intracytoplasmic Sperm Injection). The patient will be prescribed medications to prepare the endometrium. Regular ultrasound and hormonal monitoring will be performed. On the designated day, the embryo is transferred into the woman’s uterus. If there are multiple high-quality embryos, some can be frozen for future pregnancies.
Probability of success with cryopreservation programs
With the advancement of vitrification technology, the effectiveness of fertility preservation programs has matched the results of IVF with “fresh” eggs. According to the HFEA, in 2021, over 4,000 oocyte cryopreservation procedures were performed in the UK, compared to 400 in 2011.
The percentage of viable and intact cells after thawing is quite high. Current data indicate that egg freezing is a safe method for preserving reproductive potential, which helps reduce the risk of infertility due to age-related changes, although complete fertility cannot be guaranteed.
Several factors influence a patient’s chances of having a child using thawed oocytes:
- The woman’s age;
- The woman’s overall health;
- The quantity and quality of successfully frozen and thawed eggs;
- The success of the ICSI procedure;
- The subsequent development of the embryo.
A study examined the outcomes of thawed oocytes after cryopreservation. The average viability rate for women was 74%, with a pregnancy rate after embryo transfer of 48% and a live birth rate of 35%. Researchers also noted that thawing success was higher in younger women and those who had frozen more than 15 eggs.
In another study, 64% of women aged 37 and older who underwent egg freezing wished they had done so at a younger age, as this affected the number of eggs successfully frozen. About 48.2% of participants were completely satisfied with the overall number of frozen eggs. The majority of women (96.2%) did not regret the procedure.
In the UK today, women are offered fertility tests to assess ovarian reserve based on anti-Müllerian hormone levels, which reflect the number of follicles in the ovaries. By assessing their ovarian status, women can plan their pregnancies more effectively.
Possible risks and side effects of the procedure
Cryotechnology has marked a significant breakthrough in the field of reproductive medicine, allowing women to take control of their biological clocks. However, unfortunately, not all women manage to conceive or carry a pregnancy to term. The potential risks are particularly associated with the patient’s age. As a woman ages, the risks of developing gestational diabetes and fetal growth restriction increase.
One of the rare complications that can impede the retrieval and cryopreservation of oocytes is ovarian hyperstimulation syndrome. Under the influence of hormonal medications, the ovaries enlarge, and sometimes, when too many follicles are developing, this process can escalate into ovarian hyperstimulation syndrome. In such cases, the hormonal stimulation protocol must be carefully tailored.
Occasionally, women may experience premature ovulation, where the egg is released earlier than the scheduled retrieval. In these instances, the stimulation protocol should be adjusted. Furthermore, the side effects of hormonal stimulation may include increased emotional sensitivity, depression, concentration and memory issues, and drowsiness. Therefore, before beginning hormonal treatments, all patients should be fully informed about the potential side effects.
Risks may also be associated with the oocyte retrieval procedure itself. For instance, bleeding, usually minor, can occur during or after oocyte retrieval.
Complications can also arise from not following the doctor’s lifestyle recommendations. Excessive physical activity should be avoided before oocyte retrieval. Additionally, very active sexual activity after the procedure can negatively impact the woman’s health.
Cases of pelvic inflammatory processes due to the exacerbation of latent infections are extremely rare. It is crucial to initiate appropriate treatment promptly in such situations.
Despite the growing popularity of oocyte cryopreservation as an effective procedure for preventing infertility, there is still insufficient data on its long-term effects. Further research is needed to obtain more accurate pregnancy outcomes and long-term monitoring of children born through cryotechnology.
Moreover, it is essential to provide women with factual and realistic information about oocyte cryopreservation so that they can make informed decisions. Comprehensive counseling should be provided to patients, covering the benefits, risks, personal chances of success, and alternative reproductive options.
Conclusions
Today, reproductive specialists increasingly recommend that women freeze their oocytes to use them in the future when planning a pregnancy. Cryotechnology has made it possible to delay motherhood and have a child at the right time in life. Moreover, this method has opened up opportunities to address the issue of infertility, which affects both women and men worldwide. Oocyte cryopreservation is particularly relevant in the context of age-related changes. Since the youth of the body is not eternal, it is wise to take steps to preserve fertility in advance.