A frozen embryo transfer (FET) treatment cycle is where embryos which were frozen following IVF treatment are thawed (warmed) and transferred (implanted) into the womb at a later date.
There is an increasing trend to go for frozen embryo transfers more often than the traditional fresh cycle transfer process. It has been particularly advantageous in cases of subsequent IVF cycles when the initial cycle is unsuccessful, or be performed years later when the patient is ready to have another child or where fresh transfer has been deferred primarily in view of suboptimal endometrium and/or hormonal milieu. Spare embryos from your IVF treatment can be frozen for future use, depending on their quality. One of the ways we can ease the physical, financial, and emotional burden of undergoing multiple IVF cycles is through the use of cryopreserved, or frozen, embryos , as doing FET has proven to be much more cost effective. It can’t be emphasized enough that a robust cryopreservation programme and embryology personnel competent in Freeze thaw process is quintessential. We, at Anmol Fertility & IVF Centre, essentially use Vitrification, the most advanced technology in cryopreservation and have obtained consistently over 98% post thaw (warming) survivals and high success rates with FET.
In IVF-ICSI, we create embryos by fertilizing eggs with sperm. Once an embryo is formed, one of three things with it can be done :
- put it in the uterus right away in the same cycle – this is called a FRESH embryo transfer
- freeze it and sometime later (typically 1-2 months) do a FROZEN embryo transfer
- biopsy it to test for chromosome complement or genetic disease, then freeze it ( PGD/PGS). Once the test results are back, a FROZEN embryo transfer is performed subsequently.
Amongst these, all over the world, more and more ART specialists are getting inclined towards the option of Freezing the embryos and carrying out Frozen Embryo Transfe later. Why so?
There are some distinct advantages of carrying out a frozen embryo transfer, especially in the scenarios mentioned below.
- Safety : To avoid Ovarian Hyper stimulation syndrome( OHSS)If multiple follicles are formed during IVF treatment, cases of PCOS, the estrogen level during the IVF treatment (checked in your blood) is high, deferring the fresh cycle transfer is mandatory to prevent OHSS. FET in subsequent cycle is beneficial from the safety point of view. Additionally, there can be a negative effect on the endometrial lining so pregnancy rates can decline in these cases. In this situation fertility specialists often recommend freezing the embryos and putting them in at a later time when the hormones are optimally lower. No risk of OHSS: this is because the ovaries are not stimulated
- Sometimes the endometrial lining doesn’t look good on ultrasound during the IVF treatment and we will suggest you freeze the embryos, fix the endometrial lining and then do a frozen embryo transfer.
- There are a few other reasons we identify during the IVF cycle that might make us change plans from a fresh embryo transfer to a later frozen embryo transfer, like the elevation in serum Progesterone levels and prematurely advanced endometrium in the treatment cycle. In these cases, much better endometrial limning can be prepared and monitored in frozen embryo transfer cycle.
- Less stress: FET treatment is has a high chance of success because we only freeze top quality blastocysts and there is no ovarian stimulation, egg collection and therefore less visits to the clinic as well as less discomfort. This is particularly so in natural cycles .
- Less expensive: the cost of FET treatment is less than half or one third of a fresh treatment cycle of IVF or ICSI. During IVF cycles in which previously frozen embryos will be used, the ovulation induction and egg retrieval phases are not performed. For this reason, these cycles are significantly less expensive and involve fewer stages than the initial, traditional cycle.
- Less medication: no injections are required. The actual cycle itself is quite benign in preparation, using very little medication to prepare the lining of the uterus only.
- Frozen Embryo Transfer for maximizing IVF Efficiency: In vitro fertilization is a highly effective fertility treatment, but it is not uncommon for more than one cycle to be performed before pregnancy occurs. Frozen embryo transfer cycles are necessary for those wishing to use their previously stored embryos.
- Good success rates with Frozen embryos: The success rates of FET treatment are similar to fresh IVF or ICSI treatment. In some cases the success rates are in fact higher because the lining of the womb is not over-stimulated by high estrogen levels. The success rate also depends on the age of the woman when the embryos were frozen and not when transferred. Once thawing is complete and the healthy embryos are selected, the chance of successful implantation and pregnancy after frozen embryo transfer is about equal to that of a fresh transfer procedure.
- Other options for these frozen embryos can be sought after: (with expressed written consent of the couple) would be donation to another infertile couple, use in research or the embryos could be thawed and disposed of in an ethical fashion.
What are the different types of FET?
There are following main options for frozen embryo transfer treatment:
- Programmed Medicated Cycle FET( Medicated with estrogen and progesterone (MEDICATED FET)( more commonly used ) In a programmed FET you take medication, usually Estradiol tablets or patches to grow the lining of the womb until such a stage they are ready to receive embryos for implantation. Usually for 2 weeks and this is followed by progesterone pessaries to support implantation and development of the baby until 12 weeks of pregnancy.
We have to time the transfer of the embryo(s) so the uterus has been exposed to the right duration and dose of estrogen and progesterone beforehand. This can be done through medications (medicated frozen embryo transfer or FET) They allow us to time the transfer precisely, they involve fewer blood tests and ultrasounds for patients, and historically most studies showed a higher pregnancy rate than with natural cycle FETs. We can replicate them with good consistency and that also allows us to analyze uterine receptivity with ERA
- No estrogen, trigger ovulation and use progesterone (MODIFIED FET). Modified natural cycle FETs involve monitoring for ovulation and triggering the woman to ovulate with a shot of HCG. Progesterone is started in many of the cases and the transfer is scheduled according to the frozen embryos. But here are a few problems with the modified protocol like some women do not grow a follicle to trigger or don’t ovulate or some women will ovulate before the trigger shot can be given.
- In a natural cycle (natural cycle FET) if the woman cannot take estrogen or progesterone, the woman requests (perhaps she had a pregnancy from a previous natural cycle FET or simple preference), or medicated FETs don’t work. This is used in women who have regular cycles and ovulation, no drugs are used. Embryos are transferred after a positive ovulation test.
It is important to note that fair number of modified or natural cycle FET cycles are cancelled – more often than medicated. Cancelled FETs cycles are extremely upsetting for patients.
Process of FET and endometrial preparation:
With a stimulated frozen cycle, patients take medication to go through the process of down-regulation. This temporarily shuts down your ovaries and prevents any eggs from being released. You will have a scan on day two or three of your period and start taking medication to prepare your womb for the embryo transfer. A second ultrasound scan at day eight or nine will be performed to check the thickness of your endometrium. It is still necessary to closely monitor, or even control, the progression of the menstrual cycle. Because the frozen embryo transfer procedure must take place at precisely the time when conception would naturally occur, frequent ultrasounds and blood tests when required will be performed during the first 10 to 15 days of the cycle. Once it is of the appropriate thickness, and when the cycle has reached the correct stage, two to three frozen embryos will be selected and thawed. We can time the embryo thawing process and plan your transfer. The frozen embryo transfer procedure takes place in exactly the same way as a fresh embryo transfer. A thin catheter is inserted into the uterus through the cervix. The embryos are then introduced into the uterine cavity through this tube. The procedure takes very little time and there is very minimal discomfort. The actual transfer of the thawed embryos is usually performed without anesthesia and is essentially non-invasive.
At Anmol Fertility & IVF Centre, we use the most advanced technique known as “vitrification” however, not every embryo created is suitable for freezing, our Embryologists work out which embryos meet the criteria and inform you of the possibility to freeze embryos. The embryos are usually frozen and stored on the 3rd day or at blastocyst stage 5-6 days after egg collection. It is important for patients to focus on the fact that a successful embryo cryopreservation program offers patients realistic pregnancy potential from their frozen embryos.