Thanks to embryo freezing, high-quality embryos can be preserved and used in the future without the need for another egg retrieval procedure. In some patients, instead of a fresh embryo transfer, all embryos are frozen. This procedure is also referred to as freeze-all. In other patients, the embryos remaining after treatment are preserved for a future pregnancy. Which approach is appropriate is not determined by a single rule but is planned according to the couple’s clinical condition.
For couples planning IVF treatment in İzmir, the decision to freeze embryos should not be regarded as a routine step of treatment. A personalized treatment plan is created by evaluating the woman’s age, ovarian response, embryo quality, endometrial preparation, and previous treatment history together.
Therefore, when obtaining information about the embryo freezing process in İzmir, both the experience of the embryology laboratory and the clinical follow-up approach should be considered together. Choosing an IVF specialist in İzmir also becomes important at this point. This is because the timing of freezing, thawing, and embryo transfer is part of a comprehensive treatment plan that may affect the couple’s chances of pregnancy.
Embryo freezing is referred to in medical terminology as cryopreservation. The aim is to suspend the biological processes within the embryo by keeping it in liquid nitrogen at minus 196 degrees Celsius and to thaw and use it when needed.
The multicenter study by He and colleagues published in 2026 also defines embryo freezing as the storage of embryos at ultra-low temperatures and their return to normal physiological temperature when required.
The critical issue here is the formation of ice crystals. If ice crystals form inside the cells, the cell membranes may suffer irreversible damage. To prevent this, the embryo is prepared with protective solutions called cryoprotectants and frozen after being transformed into a glass-like state. This method is called vitrification.
The 2024 review by Sciorio and colleagues states that vitrification is the current standard approach that has replaced the older slow-freezing method.
Embryo freezing is performed by preparing selected high-quality embryos with special protective solutions in the laboratory, rapidly freezing them using the vitrification method, and storing them in liquid nitrogen.
The process begins with the evaluation of embryos whose development has been monitored in the laboratory after egg retrieval and fertilization. Embryologists examine the embryos according to their rate of development, cellular structure, and quality characteristics. The embryos considered suitable for freezing are prepared with special protective solutions.
Today, most centers use the rapid freezing method known as vitrification. In this method, the embryo is converted into a glass-like state within a very short time and stored in liquid nitrogen at minus 196 degrees Celsius. Thus, the biological activity of the embryo is temporarily suspended.
Embryo freezing may become an option at different stages of the treatment process. The most common situation is when high-quality embryos remain after a fresh embryo transfer. These embryos can be preserved for a future treatment attempt or for a sibling pregnancy.
In some patients, however, no fresh transfer is performed during that treatment cycle, and all embryos are frozen. The same multicenter study lists the conditions leading to this approach. These include the risk of ovarian hyperstimulation syndrome (OHSS), an endometrial environment unsuitable for fresh transfer, and the need for preimplantation genetic testing (PGT).
Embryo freezing also plays a role in fertility preservation. Before cancer treatment or in women with diminished ovarian reserve, embryos can be preserved for future use.
Embryos are most commonly frozen on the fifth or sixth day, at the blastocyst stage. A blastocyst is the advanced developmental stage in which a fluid-filled cavity has formed inside the embryo and the cells have begun to differentiate into their specific functions. The review by Sciorio and colleagues also states that current vitrification practices are predominantly performed at the blastocyst stage.
The main purpose of embryo freezing is to preserve embryos with the potential for viability. When more than one high-quality embryo is obtained from a single egg retrieval procedure, the embryos that are not transferred can be preserved for future treatment attempts. This allows the couple to maintain their chance of pregnancy without undergoing another ovarian stimulation and egg retrieval process.
Situations in which a fresh embryo transfer is considered risky also make embryo freezing a preferred option. If the risk of OHSS is high, if the endometrial lining is not adequately prepared, or if genetic test results are pending, freezing the embryos and transferring them during a more suitable cycle may be preferred. This approach aims to transfer the embryo at a more favorable time.
As the transfer day approaches, the embryo is thawed in the laboratory under controlled conditions. During the thawing process, the embryo is removed from liquid nitrogen and gradually prepared for normal physiological conditions using special solutions. At this stage, the embryo’s cellular integrity and viability are evaluated.
Most thawed embryos are able to maintain their viability. Nevertheless, it cannot be guaranteed that every embryo will survive the thawing process in the same way. The quality of the embryo before freezing, its developmental stage, and laboratory conditions may all influence the outcome. The embryo considered suitable is transferred into the uterus of the prospective mother on the day when the endometrial lining is ready.
Implantation is not an event that can be fixed to a single day on the calendar. The embryo implants into the uterus during a short and specific period known as the implantation window. Therefore, the day on which implantation occurs after frozen embryo transfer may vary from one patient to another and cannot be expressed with a single number.
The main factor affecting the timing is the developmental stage of the transferred embryo. A blastocyst-stage embryo is transferred at a stage that is already close to implantation. An embryo transferred at an earlier cleavage stage is expected to continue its development first. The second determining factor is the synchronization between the developmental day of the embryo and the preparation day of the endometrial lining.
There should be no rush to perform a pregnancy test after frozen embryo transfer. The timing of the test may vary depending on the developmental stage of the transferred embryo and the follow-up protocol of the treatment center. In general, a blood beta-hCG test is requested approximately 9 to 12 days after embryo transfer. Early home urine pregnancy tests may produce misleading results. Therefore, the most accurate assessment is made with the blood test performed on the day determined by the treating physician.
The timing of frozen embryo transfer is planned according to the period when the endometrial lining is most suitable for pregnancy. Two main approaches are used for this preparation. The first is the natural cycle approach, in which the woman's own natural menstrual cycle is monitored. The second is the hormone replacement approach, in which the endometrial lining is prepared with estrogen and progesterone support.
The COMPETE randomized trial conducted by Liu and colleagues in 2025 compared these two approaches in women with regular ovulation. In the first embryo transfer, the live birth rate was 54% in the natural cycle group and 43% in the hormone replacement group (RR 1.26, 95% confidence interval 1.10–1.44). The rates of miscarriage and antepartum bleeding were also lower in the natural cycle group. However, because this single-center study allowed crossover between the groups, the certainty of the direct comparison between the two approaches is limited.
There is an important limitation here. The natural cycle can only be considered an option in women who ovulate regularly. In women with irregular or absent ovulation, for example those with significant polycystic ovary syndrome, the natural cycle cannot be applied, and preparing the endometrial lining with hormonal support may be an appropriate choice. In other words, the hormone replacement protocol is not an inferior protocol; it addresses the needs of a different group of patients.
Frozen embryo transfer (FET) is not performed according to the same template for every patient. The medication protocol used to prepare the endometrial lining, the day on which the embryo will be thawed and transferred, and the number of embryos to be transferred are determined according to the couple’s clinical condition. Decisions such as the fertilization method are made before freezing, during the stage when the embryos are obtained.
The IVF and frozen embryo transfer process progresses in a controlled manner in most patients. Nevertheless, some symptoms require prompt evaluation. If any of the following situations occur, it is recommended that you contact the clinic managing your treatment rather than waiting.
• Heavy, bright red, and persistent vaginal bleeding after embryo transfer
• Severe pelvic pain or lower abdominal pain on one side
• Shortness of breath, chest tightness, or marked weakness
• Rapid weight gain after egg retrieval
• Significant abdominal swelling, tightness, or progressively increasing discomfort
• High fever
• Fainting sensation, dizziness, or a marked deterioration in your general condition
• Pain that does not decrease despite pain medication or gradually becomes more severe
These symptoms do not always indicate a serious problem. However, conditions such as ovarian hyperstimulation syndrome, infection, ectopic pregnancy, or bleeding require timely evaluation. Therefore, if you notice any unusual symptom, the safest course of action is to contact your physician or your IVF center.
The first step in the embryo freezing process in İzmir is not to proceed directly with the procedure but to clarify why embryo freezing is needed and at what stage it should be performed. Whether high-quality embryos remaining after a fresh transfer will be preserved or whether all embryos will be frozen is determined according to the patient's clinical condition.
Frozen embryos are stored in liquid nitrogen at minus 196 degrees Celsius. The Clinical Embryology Good Practice Framework (ARCS 2024) states that cryostorage facilities should be monitored with alarm systems that alert staff whenever storage conditions fall outside safe limits. The same framework also recommends that every step, including the storage and removal of embryos, be documented by an authorized person or a validated witnessing system. This traceability is an essential part of ensuring the safety of the process.
In Türkiye, embryo freezing is regulated by the current Assisted Reproductive Treatment (ART) Regulation issued by the Ministry of Health. According to this regulation, first published in 2014 and updated in subsequent years, embryo freezing and thawing procedures are performed with the written consent of both spouses and are legally applicable only to married couples. The maximum storage period is five years. If storage exceeds one year, the couple must submit a signed petition each year confirming their wish to continue storage. Storage beyond five years is subject to the approval of the Ministry.
To plan your embryo freezing and frozen embryo transfer process in İzmir based on your individual clinical data, you can contact Associate Professor Dr. Funda Göde. At our center in İzmir, we can evaluate your IVF treatment process together in light of the latest scientific literature and advanced laboratory techniques.
In Türkiye, embryos are stored for a maximum of five years according to the current IVF regulations. Extending this period requires the couple to submit a signed application each year, and for storage exceeding five years, it requires permission from the Ministry.
Current protocols indicate that the vast majority of thawed blastocysts maintain viability. However, this rate can vary between centers and laboratories. The quality of the embryo before freezing and laboratory conditions affect the outcome and do not constitute a guarantee.
The current vitrification method aims to preserve embryo integrity by preventing ice crystal formation and is a widely used method.
Embryo freezing is a procedure performed on embryos in a laboratory. It is not a painful procedure directly applied to the expectant mother. Pain or tenderness may be more related to the egg retrieval process.
Frozen embryos can retain their pregnancy potential when stored under appropriate conditions. Whether fresh or frozen transfer is more suitable is determined not solely by the embryo, but also by intrauterine preparation, hormone levels, OHSS risk, and treatment plan. Therefore, it is not correct to automatically consider frozen embryos as weaker.
It would be inaccurate to give a single success rate. The outcome varies depending on factors such as the mother's age, the embryo's genetic and morphological status, the intrauterine environment, and the transfer process.
Embryo freezing allows for the preservation of high-quality embryos obtained from an egg retrieval cycle without discarding them. This gives couples multiple chances for transfer from the same treatment, maintaining a cumulative pregnancy probability. However, this does not mean that freezing alone guarantees pregnancy. The decision is made based on the number and quality of embryos, as well as the couple's clinical condition.
Note: This content is for general informational purposes only and does not replace diagnosis or treatment. A physician evaluation is required for personal diagnosis and treatment planning.
