Elective frozen embryo transfers are becoming more common in IVF but do they really result in better outcomes? More clinics are considering the benefits of this approach even as fertility experts around the world continue to debate the advantages of fresh vs. frozen embryo transfer in IVF.
So why are some doctors favoring the use of frozen embryos, even though it adds to the patient’s expense? Are there any legitimate studies that validate the freezing of embryos for all IVF patients? We dig:
What is frozen embryo transfer?
In a standard IVF procedure, the embryos formed after the fertilization of male and female gametes are allowed to grow for 3-5 days and then transferred back to the uterus of the female, where they are expected to get attached and start to grow.
This is known as fresh IVF cycle or IVF with fresh embryo transfer.
In a typical IVF cycle, especially for a young couple, multiple embryos are formed. Some may even have 8-10 embryos and if they are considered to be good quality, the doctor may decide to freeze them at that stage.
Most doctors will transfer only one or two embryos in a fresh cycle and if none of them bring a positive result, you can rely on the frozen embryos for another chance, without having to repeat the whole IVF process.
One or two of your frozen embryos will be thawed (de-frozen) and transferred back to your uterine cavity. This process is called frozen embryo transfer (FET).
Now, some clinics and doctors are choosing to forego the fresh embryo transfer and instead asking patients to return in 1-2 months for FET.
Benefits of frozen embryo transfer
Doctors advocating for elective frozen embryo transfer believe that stimulation injections given during an IVF cycle are sometimes harsh on the body and cause the normal chemical balance to be thrown off.
By opting for frozen embryo transfer, they allow the body to return to its natural state, which is possibly more conducive for pregnancy.
Frozen embryo transfer is expected to bring about:
- Better embryo implantation
- Increased rate of live birth after IVF
- Reduced rate of miscarriage
- Lower stress – Since the eggs have already been collected and embryos formed, most people are relaxed as major part of the treatment has been done a month or two ago.
- Healthier babies – As the mother’s body is allowed some time to recover after administration of strong medications.
During an FET, you will not be subject to intensive hormone sessions, as egg collection is done previously. Now you only need estrogen and progesterone to thicken the uterine lining to prepare it for receiving the embryo but these do not affect the body as adversely as stimulation injections can.
- Can schedule the pregnancy – Another advantage of FETs is that you are not bound by treatment schedule. You can get the embryo transfer as soon as you feel ready for pregnancy.
Increasing the time span between administration of stimulation and the commencement of pregnancy also lowers the risk of ovarian hyperstimulation syndrome (OHSS), which can be a potentially fatal side effect of hormonal injections.
Disadvantages of frozen embryo transfer
- Added expense to the patient – the process of freezing and thawing an embryo is an extra step that incurs additional expense, which has to be borne by the patient.
- Requires more time and possibly an additional trip – While a typical IVF cycle requires 15-18 days at one stretch, the use of frozen embryos means you will have to return to the clinic again in two months.
If you, like many of our clients, are seeking treatment at an IVF clinic overseas, the transfer of frozen embryos will require you to take a second trip.
- Possibility of harming the embryos – Embryos are delicate and they need a lot of care in the freezing and thawing process. If not performed by an experienced IVF specialist, there is a risk of harming the embryos, especially during their thawing.
Some of our IVF doctors in Malaysia, have adopted the most advanced Cryotec Vitrification and Warming Method that allows them to achieve a 100% freeze-thaw survival rate.
Window of receptivity
During the ovarian stimulation in your IVF, estrogen and progesterone levels may rise upto 10 times their normal levels, which is an indication for the uterus to prepare for pregnancy.
However, the embryo is not yet ready to be transferred. Typically, we wait for 5 days to let it grow to the blastocyst stage before it can be transferred to the uterus. In these 5 days the window of receptivity may have passed, and the uterus is not as conducive to receiving the embryo.
However, this shift is not the same for all patients. Women who, at the time of the trigger shot, have high progesterone levels (over 1.5 ng / mL) are more likely to miss the window of receptivity in fresh transfer.
In women in endometriosis, ovarian stimulation causes a spike in estrogen levels, which is again not ideal for ET.
By opting for frozen embryo transfer, the doctors can remove this uncertainty and coincide transfer of embryo with the optimum uterine receptivity, thus increasing the odds of success.
Does research favor FET?
A study published in the New England Journal of Medicine found that the rate of live births did not differ significantly between fresh or frozen embryo transfer in ovulatory women, but the researchers did find that FET lowered the risk of the ovarian hyperstimulation syndrome.
In a different research, around 83,000 IVF patients were studied and it was found that FETs are not the standard solution for all cases. The method of embryo transfer should depend upon the number of eggs retrieved from the patient.
Depending upon how the patient responds to the stimulation medication, the number of eggs collected is variable, and patients are classified as:
- Low responders – produce one to five eggs
- Intermediate responders – produce six to 14 eggs
- High responders – produce 15 or more
The study, published in the journal Fertility and Sterility, found that freezing the embryos was beneficial on in high responders i.e. patients who produced more than 15 eggs. In this group, the clinical pregnancy rate (CPR) was 61.5% with FET but 57.4% with transfer of fresh embryos.
In intermediate responders the CPR was 44.2% with FET, while it was 49.6% with fresh transfer. Similarly, in low responders the CPR was found to be 15.9% in frozen transfer vs. 33.2% in fresh transfer.
This indicates that the number of eggs collected is more important for IVF success than the method of embryo transfer, and that a freeze-all strategy is not called for.
So should you freeze the embryos?
More concrete research is required in this direction before we can confidently adopt the freeze-all policy for embryos in IVF cycles, even though many doctors across the world are following this practice.
Consider the pros and cons of freezing the embryos and then discuss with your doctor regarding which approach could bring better results for you.