What is an embryo transfer?
An embryo transfer is the final step in the fertility treatment plan. When most IVF patients complete their cycle, they anxiously await the possibility of getting pregnant—it has been hard work up until this point!
An embryo transfer consists of taking the embryo created in the lab after the IVF cycle and transferring it back into the uterus. Embryo transfers can happen as part of the IVF cycle itself or can be completely separate treatment cycles that take place later. There are two types of embryo transfers: a fresh transfer and a frozen transfer.
Types of embryo transfers.
1. What is a fresh embryo transfer?
A fresh embryo transfer (“fresh transfer”) is a transfer that happens at the end of an IVF cycle, a few days after the egg retrieval.
For a fresh transfer, a patient goes through the IVF stimulation process for approximately 10 to 12 days and then completes the egg retrieval. Once the eggs are retrieved, they are fertilized in the lab and allowed to grow. The patient will start on estrogen and progesterone supplements following the egg retrieval to prepare the Endometrial lining for the embryo to be transferred back into the uterus. Typically, the embryo is transferred back into the uterus after 5-6 days of developing in the lab.
Fresh transfers are recommended for a few types of patients, including:
patients who are seeking the shortest wait time to try to conceive;
patients who do not want to pay to store frozen embryos; and
patients who have historically had embryos that do not develop well in the lab.
If you are a patient that is deemed to be high risk for Ovarian Hyperstimulation Syndrome (OHSS), which can cause severe symptoms following the egg retrieval, your doctor will likely steer you towards a frozen embryo transfer. This recommendation would allow your body to recover from the IVF cycle and be ready for the embryo transfer cycle once your body and hormones are back to baseline.
2. What is a frozen embryo transfer (FET)?
For a Frozen Embryo Transfer (FET), a patient goes through the IVF stimulation process for approximately 10 to 12 days and then has the egg retrieval. After retrieval, the eggs are fertilized in the lab and allowed to grow. Once the embryos reach a certain stage of maturity known as a Blastocyst, they are frozen for later use. FET is now the predominant method used throughout the reproductive endocrinology field.
There are two types of frozen embryo transfers: natural and medicated
a. Natural FETs are timed along with the patient’s natural menstrual cycle and ovulation. In a natural FET, the body grows its own Dominant Follicle as it naturally does monthly. In response to the growing follicle and estrogen level, the uterine lining grows thick enough for an embryo to implant. When the lining is ready, the patient will begin taking progesterone to prepare the lining to transfer the embryo. Only patients with regular menstrual cycles and confirmed ovulation can do natural transfers.
b. In a medicated FET cycle, the lining is grown using estrogen pills or injections, and the ovaries never grow a follicle. The estrogen causes the growth of a uterine lining thick enough for transfer and then the patient is informed to begin progesterone supplementation to prepare the lining for the embryo transfer. Most patients qualify for medicated FET.
Your fertility specialist can talk with you about your menstrual cycle and ovulation and can show you whether a natural or a medicated FET cycle would work best for you.
Frozen embryo transfers are preferred for a few reasons:
Flexible Timing: In a medicated FET cycle, the estrogen and progesterone medications allow for the manipulation of the transfer date within a certain window. This flexibility lets the patient work around their personal schedule and their doctor’s schedule when planning the transfer.
Genetic Testing: FETs also provide the opportunity to do Preimplantation Genetic Testing biopsies of the embryos. PGT results take around 10-14 days to get back, which means that the embryos must be frozen while awaiting the results. Once the results are received, the FET cycle can be planned using an embryo whose chromosomes have been confirmed to be normal. This process increases the odds of a successful transfer and pregnancy.
Family Planning: Lastly, freezing the embryos allows patients to plan for more children in the future if there are multiple embryos available for freezing.
Depending on your clinical situation and medical history, your reproductive specialist will be able to help you decide which type of transfer is best for you. Every patient and every cycle is different. In some cases one patient may try both a fresh and a frozen transfer at different times throughout their fertility journey.