If you’re considering in vitro fertilization (IVF), you may have come across talk of frozen embryo transfer, or FET. To continue helping you sort through the alphabet of IVF, we’ll explain FET in this blog and how it might be able to help you achieve the family you want.
What are frozen embryos? As part of your IVF treatment, you will take medications to stimulate production of your eggs. Your doctor will then retrieve the eggs and enable your partner’s sperm to fertilize them in a laboratory dish. Then, your doctor will transfer the fertilized egg, now called an embryo, back into your uterus to start a pregnancy.
Sometimes more embryos are generated than you want to transfer. Medical experts often advise transferring one embryo per attempt to minimize potential pregnancy complications of carrying multiples. Fortunately, technicians can freeze and store (cryopreserve) these remaining IVF embryos for future attempts at pregnancy. These stored embryos can be thawed later and transferred in a procedure called a frozen embryo transfer.
How are embryos frozen? Embryos are prepared for freezing in the IVF lab using a process that removes the liquid inside the cells, replacing it with a protective solution that prevents damage at below freezing temperatures. The embryos are then frozen at very low temperatures that temporarily stop cell functions until the embryos are thawed.
When are embryos thawed? If your fresh IVF cycle was unsuccessful, embryos can be thawed and transferred as soon as a month after the failed cycle. If the cycle was successful and resulted in a live birth, you can wait until you’re ready to have a second child before thawing the remaining embryos. The good news is that embryos can be safely stored for many years without damage at very low temperatures.
What happens in preparation for an FET? In a normal menstrual cycle, the body produces hormones that encourage eggs to grow and ovulate. These hormones also cause the uterine lining to become lush and thick in preparation to receive an embryo if the egg is fertilized. Your doctor will prescribe hormonal medications to prepare your uterine lining for the transfer. Your doctor will monitor your uterine lining by ultrasound to see that it is getting thicker and ready for the embryo transfer.
When your doctor decides you are ready, he will schedule an embryo transfer. Your doctor will discuss with you the number and quality of your embryos and recommend a plan for how many should be thawed and transferred. Depending on the developmental stage at which the embryo was frozen, your embryos may be thawed a day or more in advance to allow them to grow a little more. If your embryo was frozen at a later developmental stage (blastocyst stage), there may be only a few hours between the thaw of the embryo and the transfer.