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Is freezing embryos the future of IVF?

Is freezing embryos the future of IVF?
Is freezing embryos the future of IVF?

According to the latest HFEA Trends and Figures report published in May 2019, Frozen Embryo Transfer (FET) cycles have increased by 11% between 2016 and 2017 whilst the number of fresh embryo transfers has dropped by 2%.  For the first time, Frozen Embryo Transfer cycles are now more successful than fresh (23 vs 22%) based on the HFEA’s national figures.

We sat down with Andrew Thomson, the Laboratory Manager at LWC Wales and Bristol to discuss this new trend.

Why have Frozen Embryo Transfer cycles seen such an increase?

During an IVF cycle we stimulate the patient’s ovaries before an egg collection procedure takes place. The collected eggs are then fertilised in the laboratory using IVF or ICSI to create embryos. The embryos are then cultured in the laboratory for around 5 days and closely monitored by a team of highly-skilled embryologists.  Traditionally, we then replaced the best embryo (or sometimes two) back to the patient on day 5 and freeze any remaining good quality embryos.

Using the latest vitrification technology, embryos don’t deteriorate once frozen they are preserved at the age you are at the time of freeze. For example, if you were aged 35 when you froze the embryos, if you use them 5 years later, the embryos will still be 35! This means that today embryos can be thawed out and replaced in a Frozen Embryo Transfer (FET) cycle, when the patient is ready, with the same or better chance of success than in a fresh cycle.

Over the last few years, the scientific community have found that embryo transfer in a frozen cycle may produce better results.  Due to the stimulation medication a patient is given prior to egg collection and the trauma of the egg collection procedure itself, an embryo transfer during this same cycle may not be the best or safest time.  It could also reduce the chance of pregnancy.  More clinics are opting to freeze the embryos and replace them in an FET cycle a month later or when the patient is ready.

An FET cycle uses minimal or no medication so one embryo can be replaced into a much more natural environment resulting in potentially higher success rate and hopefully a safer pregnancy. There has been a lot of research on this topic but at present there is still no consensus as to the best policy with different clinics favouring fresh or frozen embryos. 

Has LWC Wales seen an increase in Frozen Embryo Transfer cycles?

Most definitely. The fasted growing trend in IVF is egg freezing but for us FET cycles have increased faster than any other treatment. In Cardiff, FET cycles increased by 32% (2017 vs 2018) and we’ve already done 20% more in 2019 compared to the same time in 2018!

How successful is a Frozen Embryo Transfer?

According to the latest HFEA national figures, FET is now more successful than a fresh embryo transfer.  The latest success rates from the LWC Cardiff laboratory show that we have achieved great success with our FET programme over the last 15 months. When you compare the latest HFEA verified data in our region, our Cardiff laboratory comes top!

This success has been due to the Precision Embryology we have incorporated into the laboratory. We now have two time-lapse incubators and over 98% of our patients’ embryos are cultured using this technology (fresh and frozen). Pictures are taken of the embryos every 5 minutes without disturbing their environment, so we can easily track their development. We can then freeze or transfer the embryo at exactly the right time.

Based on the precision embryology principals, the Cardiff laboratory have achieved very high standards.   On average 70% of the embryos we create make a blastocyst (a day 5 embryo required for freezing).  If a patient has 4 or more fertilised eggs, more than 50% of the time the patient will have an embryo to transfer AND embryos suitable for freezing. This means patients treated at LWC Wales will achieve a high cumulative pregnancy rate by using their fresh and frozen embryos from one egg collection.

Patients should be aware that there is a very small chance the embryos will not survive the freezing and thaw process.  In these instances, either another embryo will be thawed (if available) or the embryo transfer will be cancelled.  At LWC Wales the survival rate of our frozen embryos after thawing is over 97% which is excellent!

What is precision embryo transfer?

The latest time-lapse technology in the laboratory helps our team of highly-skilled embryologists to decide the best time for embryo transfer. Viewing embryo development allows the embryologist to confirm whether to transfer on day 5 or to freeze the embryo for transfer in a later frozen embryo transfer cycle.  This means that embryo transfer will be individually tailored to the patient to maximise success to you specifically.

This philosophy is different from standard embryology practice where embryos would be routinely replaced regardless of their development. Patients will also benefit from having a personal consultation with their designated embryologist to review the images of each of their embryos and to pinpoint exactly when the transfer will take place.

Are all embryos suitable for freezing?

At LWC Wales we only freeze blastocyst embryos that have fully expanded. For most embryos this will be on day 5 of development however sometimes this won’t happen until day 6 as some embryos are slower developmentally than others. Slow embryos are not suitable for freezing on day 5 and some clinics don’t even offer day 6 freezing meaning these embryos will be discarded.  We have found from our data that there is no difference in success between an embryo that is frozen on day 5 or day 6 which is very interesting.  

A recent study on slow blastocyst development suggests that day 6 embryos should be frozen and transferred in a later FET cycle rather than transferred fresh.  Their study showed improved success rates for these patients and our own data supports this.  The findings of our own study will be published later this year.

Is Frozen Embryo Transfer the future?

 Quite possibly. Research into fresh vs frozen embryos will continue and LWC will be at the cutting edge of it. We presented our research this year at the Fertility Conference in Birmingham and we are currently working in conjunction with Cardiff University and another research group.  We want to  ensure the quality of our programme and that patients receive the best possible outcomes.

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