What is a Frozen Embryo Transfer?

happy pregnant woman looking at ultrasound with clinician

For couples or individuals on their journey towards parenthood through in vitro fertilization (IVF), the term “Frozen Embryo Transfer” (FET) is likely to come up frequently. FET is a crucial step in the IVF process, and understanding its significance and procedure can help patients make informed decisions about their fertility treatment. We spoke with Dr. Nina Vyas, REI at California Fertility Partners, who helped us explore what a Frozen Embryo Transfer is, the FET process and procedure, benefits, and more. 

Understanding Frozen Embryos

Before delving into Frozen Embryo Transfer, it’s important to grasp the concept of embryo use and storage after an IVF cycle. During an IVF cycle, multiple embryos are often created from eggs and sperm. After this, there is an option for a “fresh” or “frozen” embryo transfer. A fresh embryo transfer is performed at the time the embryos are seen in the lab following the IVF cycle. Although, a fresh embryo transfer may be recommended in select cases, a majority of embryo transfers in the United States are performed after they are cryopreserved or frozen through a process called vitrification. In a subsequent transfer cycle, an embryo will be thawed in the embryology lab and transferred back into the uterus. In either a fresh or frozen embryo transfer cycle, if there are surplus embryos, these will remain cryopreserved for future use, offering patients the opportunity to attempt pregnancy without undergoing another full IVF cycle. The benefits of a frozen embryo transfer versus a fresh embryo transfer are highlighted below.  

Frozen Embryo Transfer is a pivotal component of assisted reproductive technology (ART) for several reasons: 

  • Fertility Preservation: FET is an option for those facing medical treatments, such as chemotherapy, radiation, or surgery, that may affect their fertility. Before undergoing these treatments, individuals can freeze embryos for use in the future, preserving their potential to have biological children. When ready to conceive, patients can undergo an FET with their frozen embryos in the hopes of getting pregnant. 
  • Optimal Timing: Not all embryos are transferred immediately after fertilization. By freezing embryos and waiting for the ideal uterine environment, implantation can occur at the most favorable time, increasing the chances of a successful pregnancy. 
  • Multiple Attempts: FET offers patients the opportunity for multiple single embryo transfer attempts without undergoing a full IVF cycle each time. This can be cost-effective and less physically demanding. 
  • Reduced Risk: In some cases, women may be at risk of ovarian hyperstimulation syndrome (OHSS) during an IVF cycle. Freezing embryos and transferring them in a separate cycle can mitigate this risk. 
  • Preimplantation Genetic Testing: For individuals or couples embarking on the journey of Preimplantation Genetic Testing (PGT) to assess the genetic health of their embryos, it’s important to note that a Frozen Embryo Transfer (FET) becomes not just an option but a necessity. The combination of FET and PGT is a meticulously planned strategy that allows for the selection of genetically normal embryos, ensuring a higher likelihood of a successful pregnancy while minimizing the risk of passing on genetic disorders.  
  • Single Embryo Transfer: FET after PGT testing will almost always be performed as a single embryo. This reduces the risk of multiple gestation (twins, triplets, etc.), allowing for a safer and healthier pregnancy and delivery.  

Frozen Embryo Transfers Compared to Fresh Embryo Transfers

While both Fresh and Frozen Embryo Transfers (FETs) are common components of assisted reproductive technology, they differ significantly in their approach and considerations: 

  • Timing: In a fresh embryo transfer, embryos are transferred to the uterus shortly after they are created, typically during the same IVF cycle. This means that there is no delay between fertilization and implantation. In comparison, a frozen embryo transfer (FET) allows for a more flexible approach. Embryos are cryopreserved and transferred in a subsequent cycle, allowing for the optimal uterine environment to be established, increasing the chances of implantation.
  • Ovarian Stimulation: Patients undergoing a fresh transfer will have just undergone ovarian stimulation with medications to encourage the development of multiple eggs. This can lead to a higher risk of ovarian hyperstimulation syndrome (OHSS) and requires close monitoring in the event of successful implantation and pregnancy.

    Since a frozen embryo transfer occurs in a separate cycle, patients are not required to undergo rigorous ovarian stimulation during a fresh cycle. This reduces the risk of OHSS, and other complications associated with high levels of ovarian hormones. 
  • Limited Flexibility: Fresh transfers offer little flexibility in terms of timing. If unforeseen circumstances, such as poor ovarian response or embryo quality, arise during the IVF cycle, the transfer may need to be canceled or delayed. In the case of cancellation or delay, the embryo would be cryopreserved and transferred in a subsequent cycle as a frozen embryo transfer. 
  • Pregnancy Rates: Studies have shown that FET can have slightly higher success rates compared to fresh transfers in certain cases. This may be because the uterine lining is better prepared and more receptive to implantation. 

Natural Cycle versus Programmed FET

There are two ways in which we can prepare the uterus for a frozen embryo transfer: a programmed cycle or a natural cycle. Here we will delve into details about both. 

  • Uterine Preparation in a Natural Cycle FET (NC-FET): In NC-FET, the patient’s natural menstrual cycle is used to prepare the endometrium. No hormonal medications are necessary, and the embryo transfer is timed to coincide with the patient’s natural ovulation. This ovulation can be triggered with a medication or can be monitored for with bloodwork and ultrasound.  
  • Uterine Preparation in a Programmed FET Cycle: Hormonal medications are used to suppress the patient’s menstrual cycle and concurrently prepare the endometrium for the embryo transfer. Estrogen and progesterone are used to mimic the natural rise and fall of these hormones in a menstrual cycle and embryo transfer is done at a precise time based on the administration of the medication.  

Natural versus Programmed FET – which is best for me? 

Ultimately, the best type of frozen embryo transfer for a particular patient will depend on their individual circumstances and preferences. Patients with regular menstrual cycles may be candidates for NC-FET cycles, as they are more natural and less invasive. Patients with irregular menstrual cycles or other fertility issues may require programmed FET cycles, as they allow for more precise control of the timing of the transfer. Your reproductive endocrinologist will review the pros and cons of each type to see which is best for you, based on your individual medical history and fertility goals. 

The Frozen Embryo Transfer Procedure 

Let’s talk about what to expect on the day of the frozen embryo transfer: 

  • Embryo Thawing: On the day of the transfer, the frozen embryo is thawed under controlled conditions. The embryologist carefully monitors this process to ensure the embryo’s viability. 
  • Transfer Procedure: The embryo transfer is a relatively simple, outpatient procedure that doesn’t require anesthesia. The embryologist loads the thawed embryo into a thin, flexible catheter. The physician will then gently place this catheter and the embryo into the patient’s uterus.  This step is guided by ultrasound to ensure precise placement. 
  • Post-Transfer Care: Following the transfer, patients are often advised to rest briefly before resuming their normal activities. Additional hormonal support may be provided to help sustain the pregnancy if implantation occurs. 
  • Timing and Success Rates: The timing of a Frozen Embryo Transfer is crucial for its success. The window of implantation, when the uterine lining is most receptive to the embryo, must be carefully calculated. This timing depends on the patient’s individual cycle and the embryo’s stage of development. Success rates for FET can vary but are generally quite high. Factors influencing success include the quality of the embryo, the patient’s age, and any underlying fertility issues. Your physician can provide a more accurate prediction of success based on individual circumstances. 

Emotional Aspects

The journey of infertility and assisted reproduction can be emotionally challenging. Patients should be aware that emotional support is available throughout the FET process. Many individuals and couples find solace in counseling, support groups, or connecting with others who have experienced similar challenges. It’s essential to acknowledge the emotional aspects of fertility treatment and seek the help needed to navigate them successfully.

Building Your Family Through Frozen Embryo Transfer (FET)

In conclusion, a Frozen Embryo Transfer is a vital step in the journey toward achieving a successful pregnancy through assisted reproduction. It offers hope to those facing fertility challenges, provides options for future family planning, and increases the chances of a successful pregnancy without the need for repeated IVF cycles. Understanding the procedure, its timing, and the emotional aspects surrounding it can empower patients to make informed decisions on their path to parenthood. If you are considering FET as part of your fertility journey, consult with your Progyny Patient Care Advocate, who can help you find a Reproductive Endocrinologist and Infertility Specialist who can provide personalized guidance and care tailored to your unique situation.