You may have heard about frozen embryo transfers and may be confused or concerned, but there is no need to be. This process simply means that instead of the female patient going through ovarian stimulation at the start of each cycle of In Vitro Fertilisation (IVF), embryos from a previous cycle are thawed ready for implant instead. This cuts down on the amount of time that is needed for each cycle, and more importantly it offers the patient the chance to use the freshest possible eggs. The quality of eggs deteriorates with age, leading to the possibility of having a more difficult time conceiving. The fresher the eggs, the better the chance that they will be of high enough quality to result in pregnancy. A patient will have enough eggs collected during her first cycle to produce multiple embryos, the eggs that are fertilised and ready to be transferred back into the uterus. IVI offers single embryo transfer during IVF, meaning that the remaining embryos can be vitrified, ready to be used in future cycles.

Who can opt for frozen embryo transfers?

IVI works with women between the ages of 18 and 50, offering the fertility treatment that is most appropriate for each patient’s individual circumstances. In general, younger women have higher quality eggs, though of course this is not true in every case. Those who have suffered through multiple miscarriages, endometriosis, or early miscarriage may have different success rates to those who have other infertility issues, and this may be down to the quality of the eggs. However, the earlier a patient visits IVI and begins the fertility treatment, the higher the likelihood that her eggs will result in embryos and ultimately result in pregnancy. Any of IVI’s female patients who go through ovarian stimulation are welcome to opt to freeze resulting embryos for future use.

Frozen embryo transfer terminology

Fertility specialists use various terms at each stage of the process. An egg is also known as an oocyte, and the egg can be collected from the female patient or from an egg donor. Once the egg has been fertilised, it is known as a zygote. When the fertilised egg has developed and reached the second stage of development, usually beginning at day 5 after fertilisation, it becomes a blastocyst. Technically, this is the correct term to use until the tenth day after fertilisation, when the blastocyst enters the third stage of development and is then referred to as an embryo. The embryo does not enter the foetal stage until week ten of the pregnancy.

While many medical professional bodies refer to embryo transfer, this is a catch-all term that generally refers to the transfer of blastocysts. Blastocysts are given between three and five days to develop before being transferred into the uterus, with later-stage blastocysts having a higher chance of resulting in pregnancy in general.

How are eggs collected, fertilised and frozen?

Female patients go through hormone treatment at the start of their first cycle of IVF. This stimulates egg production, allowing the clinic to collect multiple eggs, rather than just the single one that would be released during a natural, unstimulated cycle. Collecting multiple eggs means that the clinic is able to produce as many embryos as possible. If the patient has opted for Preimplantation Genetic Screening or Preimplantation Genetic Diagnosis, one of the blastocysts may be subject to a biopsy to investigate genetic structure and possible genetic anomalies such as Down’s Syndrome. A blastocyst will then be transferred back into the patient’s uterus. The remaining embryos can, and should, be frozen. Fertilised eggs can be frozen at any stage of the process, including from day one, but it is much more common to allow the blastocyst to develop beforehand. Research shows that there is a better chance of a successful pregnancy from a blastocyst that has been allowed to develop for five days than from a fertilised egg that is transferred earlier.

How does the frozen embryo transfer process differ from IVF with fresh eggs?

The only differences between using fresh and frozen eggs in a cycle of IVF is that the female patient will not have to go through ovarian stimulation at the beginning of the frozen embryo transfer process, and that the male patient will not need to deliver his sperm. The male patient (or indeed, sperm donor) has already played his part and his genetic material is not needed again. This is also true of the female patient (or egg donor), but she will still need to go through hormone treatment to encourage thickening of the endometrial lining. This is the part of the cycle that prepares the womb for embryo implantation. The frozen blastocyst is thawed carefully and, when ready, transferred. The rest of the cycle is exactly the same as when fresh eggs are used, and rates of success remain stable, regardless of whether a fresh or frozen embryo is transferred.

What happens after Frozen Embryo Transfer?

The remaining steps of the cycle of IVF are exactly the same. As this cannot be the patient’s first attempt at conceiving via IVF, she will be familiar with what happens over the next few days. It can be tempting to take a pregnancy test at ten days after frozen embryo transfer, but the recommended advice from IVI is to continue to wait and to take a test from fourteen days post transfer. Testing too early may result in a false negative, which can cause upset. It should be borne in mind that the waiting time between transfer and taking a pregnancy test can seem long and frustrating. The patient may have questions about what to do after a frozen embryo transfer, but the answer is really that the best thing to do is to go on with life as normal.

Chances of success with Frozen Embryo Transfer

Frozen embryo transfer success rates do not differ in any significant way from those of fresh embryo transfers. Because of the advances in modern fertility treatment, 95% of thawed blastocysts are suitable for transfer. Of course, IVI carefully thaws each frozen embryo transfer blastocyst before continuing with the next stage of the IVF cycle, meaning that only viable, high quality blastocysts are transferred. The biggest benefit to using frozen embryo blastocysts is that fresher eggs are used, improving the success rate of a second attempt overall. In Spain, where IVI has 31 clinics, waiting times are very short, but this is not the case in every country. Being able to begin another cycle of IVF immediately after a failed one, or, on the other hand, being able to give yourself time to recover and possibly grieve between IVF cycles is an important aspect that should not be overlooked. It is unfortunate when couples or single women feel forced to attempt another cycle of IVF when they may not be emotionally ready, because time is ticking by. Opting for frozen embryo transfer may be the best way to buy a little breathing space without sacrificing chances of success.

Frozen eggs and frozen embryo transfer

Frozen embryo transfer is different from using frozen eggs. Using frozen eggs in IVF means that only one or two eggs are thawed ready for fertilisation, only being prepared directly before they are needed. This means that a previously frozen egg, once fertilised, is unlikely to be re-frozen. IVI maintains that single embryo transfer is best practice, and the likelihood of blastocysts from previously frozen eggs being wasted is incredibly low. Frozen eggs have many of the same benefits of frozen embryo transfer, such as shorter waiting times for ovary stimulation, but apart from this the two procedures are very different. Women are likely to freeze their eggs so that they have the option of attempting IVF at a date in the future, even if they are not ready to start a family at that point in their lives; frozen embryo transfer comes about where patients have more than one viable blastocyst available during a cycle of IVF, where it would be prudent to freeze one to use at a later date. Using frozen eggs and frozen embryo transfer are not interchangeable, but rather mutually exclusive choices to be made when opting for IVF.

In some cases frozen embryo transfer of blastocysts may be the best possible option, especially for a couple or single woman who has been through one or two cycles of IVF previously. Success rates remain at the same level as with fresh embryo transfer, and slightly higher for some women. This is because the egg used was from an earlier time in her life, before any decline in the quality of her eggs. It is certainly an option to consider when discussing your own circumstances with the professionals at your IVI clinic.

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