A frozen embryo transfer can be an effective way to use stored embryos from previous IVF treatment. Today's technology has resulted in high freeze-thaw survival rates of embryos, and there are plenty of ways to make sure the embryos used have a high chance of survival. Here's what to expect during every step of the embryo transfer process.
What Is Frozen Embryo Transfer?
Frozen embryo transfer is the second stage of in vitro fertilization, or IVF cycle. During IVF, a woman's eggs are extracted, either during her natural production or often after using hormonal hyperstimulation medicine that triggers egg production and ovulation.
Once the healthy eggs are removed during a short procedure, lab specialists fertilize them with the sperm selection in a lab. The fertilized eggs develop into embryos, and they are often frozen to preserve them for later use.
The embryos can then be implanted into the woman's uterus anytime in the future — it can be done during her next ovulation phase after the embryo is made, or it can be further down the road, especially if she wants to have another child on her own timeline without going through IVF stimulation again.
Frozen Embryo Transfer (FET) Timeline & Process
The frozen embryo transfer timeline depends on whether a woman needs to do IVF in order to get the embryo, or if she's using previous frozen embryos. With IVF, expect the process to take about six to eight weeks. This accounts for the pre-IVF hormonal preparation, egg stimulation, ovulation and egg retrieval, sperm selection, and the embryo transfer itself.
With FET alone, the process can take three to four weeks. It starts multiple hormone treatments to prepare your body. Then the FET is then scheduled for three to six days after that, and pregnancy testing can be done around nine to 14 days after the transfer.
Consultation & Pre-Screening
The FET process starts with a consultation and pre-screening. Your fertility doctor will review your records, current and past medications, as well as your fertility history. Pre-screening includes ultrasounds and blood work to determine uterine suitability for transfer as well as monitoring the ovaries leading up to the frozen embryo transfer.
Embryologists will also review your frozen embryos and choose the one with the highest grade to use for the transfer. This is one way to maximize your chances of a successful pregnancy. This a record review and does not involve thawing the embryos.
Prior to FET, your fertility doctor will likely prescribe three to four weeks of birth control to regulate your hormone cycle. This makes it easier to control and track your cycle and prepare for the frozen embryo transfer.
As your body starts to prepare with birth control pills, you may also begin stimulation medicine. This typically involves estrogen medicine to thicken the uterine lining as happens during the first half of a natural cycle. Then progesterone injections or vaginal suppositories are then added, again mimicking what happens after ovulation, to optimize the chances of the embryo successfully implanting into the uterine lining. The frozen embryo transfer is then planned for one day during the next week after adequate progesterone exposure..
In some cases, it may be possible to do natural FET. Instead of stimulating ovulation with hormonal supplements, the process relies on a woman's organic ovulation cycle. Your fertility doctor will likely still use bloodwork and ultrasounds to monitor the thickness of your endometrium, which is an indicator of follicle growth. However, ovulation is still often triggered to ensure the timing of the frozen embryo transfer. Natural FET is best for patients who regularly ovulate during their cycles each month.
Once the endometrium is exposed to progesterone, the embryo transfer is scheduled for approximately five days afterwards. The chosen embryo will be thawed in an IVF lab by specialized embryologists. Then your fertility doctor will transfer the embryo into the uterus, using an ultrasound for guidance. It is a fast procedure that feels like a Pap smear. Afterwards, you'll continue your progesterone treatment to support a potential pregnancy. While you may look for positive signs after an embryo transfer, it's best to wait the full nine to 14 days before taking a pregnancy test.
Pregnancy Success Rates
Freezing embryos does not usually impact success rates; in fact, the chances for success can be higher with a frozen embryo than during a fresh IVF cycle. One study revealed that women older than 44 years experienced just a 1.7% success rate with fresh cycles and a whopping 9.2% for thaw cycles. The same study indicated that from 2010 to 2019, the frozen embryo live birth rate increased by 50%, whereas fresh birth rates in the same time period only rose 1%.
There are, of course, many factors affecting the success of an FET, including:
The quality and genetic content of the embryo
Benefits of Frozen Embryo Transfer
Opting for a frozen embryo transfer comes with a range of benefits.
Increased likelihood of success: Over the years, FET has become increasingly successful with live birth rates.
Use of preimplantation genetic screening: Embryologists can check for genetic disorders as well as the quality of the embryo.
More natural hormonal prep: The uterine environment is more naturally conducive to pregnancy development with FET as the estrogen levels are generally lower than with IVF stimulation.
Less demanding process: The entire process of FET is less demanding than doing a fresh IVF cycle each time. Your body doesn't have to go through as much in a short period of time, and there's a lot less appointments to schedule so you can continue with other life and work responsibilities.
Increased flexibility: The ability to do FET has uncoupled the embryo creation process from any attempts at pregnancy. This way embryos can be created and stored for use at a time that is most conducive to the patient.