Success rates in the transfer of fresh and frozen embryos during in vitro fertilization (IVF) can vary depending on several factors, and both approaches have their advantages and disadvantages. Although historically it was believed that fresh embryo transfers offered better results, advances in embryo freezing techniques, particularly vitrification, have in recent years matched or, in some cases, surpassed the success rates of fresh embryo transfers.
Regarding the advantages of fresh embryo transfers, it was once believed that fresh embryos had a higher chance of success because they were transferred within the same cycle in which the eggs were retrieved. This process avoided any potential effects that freezing and thawing could have on the embryo. The immediate transfer of fresh embryos eliminated the need for cryopreservation techniques, making it seem like the optimal approach at the time.
However, when considering the disadvantages of fresh embryo transfers, one notable issue is that the hormonal environment of the woman following ovarian stimulation may not be optimal for implantation. Hormonal fluctuations caused by IVF stimulation could negatively impact the likelihood of implantation success. Additionally, some women may develop ovarian hyperstimulation syndrome (OHSS), which can further reduce the chances of a successful fresh embryo transfer.
When it comes to frozen embryo transfers, several advantages stand out. One of the most significant benefits is that cryopreservation allows for the transfer to be performed in a different cycle from the ovarian stimulation. This gives the woman’s body time to return to a more natural hormonal state, which can optimize the endometrial environment for implantation. Moreover, vitrification, a rapid freezing technique, has proven to be highly effective, with very high embryo survival rates after thawing.
On the downside, despite significant advancements in cryopreservation technology, there is always a small risk that some embryos may not survive the freezing and thawing process. However, with modern vitrification methods, this risk is extremely low.
But what does the scientific evidence say? Recent studies have shown that the success rates (clinical pregnancies and live births) of frozen embryo transfers have matched, and in some cases even surpassed, those of fresh embryo transfers. This is particularly true in certain patient groups, such as women with polycystic ovary syndrome (PCOS) or those at risk of OHSS. Additionally, some research suggests that frozen embryos may have higher implantation rates due to a more favourable endometrial environment at the time of transfer.
In conclusion, success rates can be similar between fresh and frozen embryo transfers, but the choice of approach depends on the individual clinical situation. In many cases, frozen embryo transfer has become the preferred option due to its flexibility and the potential for improved endometrial conditions, which may enhance pregnancy rates.
Actually the jury is still out on that because there’s several trials that are being done around whether we should be freezing for all or whether we should be doing fresh transfers. In my opinion, if the patient is not hyper-stimulated at all in the fresh cycle, then certainly she can attempt a fresh embryo transfer. I’m very mindful at the fact that when we give hormones to produce or to induce eggs being formed in the ovary which is part of a fresh cycle, then that raises the estrogen levels in the woman’s body which can, if elevated to a very high degree, lead to hyper-stimulation and even potentially a lower implantation potential and that’s why the debate that in patients with a very high level of estrogen, we should not be doing a fresh embryo transfer. We should be performing a frozen embryo transfer. However, the trend nowadays is more moving towards performing frozen embryo transfers in more than 80% of the patients, so likewise we have seen the same statistic on more patients going towards frozen embryo transfers than fresh embryos but we haven’t closed the door on fresh embryo transfers. Our preference is always to do frozen embryo transfers, so that the patient totally recovers after all those hormones that they’ve taken to stimulate the ovaries and can stop the process after the egg collection. Let all those hormones wash out and then come back after another cycle, just a clear menstrual cycle come back and have your embryo transfer rather than just feeling rough as a result of all those hormones and if a pregnancy establishes that feeling will last even longer of not feeling well.
No, they are not. Nowadays, a fresh embryo transfer has a higher success rate, and always, if possible, we try to perform fresh embryo transfers with own eggs and IVF stimulation, or with donor eggs. Of course, frozen embryos or FET (frozen embryo transfer) is a method also with a high success rate and always, if there are embryos left on the day of the fresh embryo transfer, we freeze them. Because we believe in frozen embryo transfer and most of the time patients get pregnant. Of course, there are situations where we are not able to perform a fresh transfer for example; during hyper-stimulation, bad quality endometrium, high progesterone at the beginning of the cycle, and so we have to freeze all the embryos. But we believe that the frozen embryo transfer in one of the subsequent cycles and it also has a high success rate.
Fresh and frozen embryo transfers should offer the same pregnancy rates as long as you work with blastocysts – the embryos on day 5. The new freezing technique – vitrification – has completely changed the scenario. With this technique, blastocysts have a survival rate higher than 98%. When we have problems during an egg donation cycle, for example, a breakthrough bleeding or when we feel that there is a really high risk of having hyperstimulation syndrome during IVF, we don’t mind freezing all the embryos.
We know that the first cryotransfer is going to offer the patients the same success rates as the fresh embryo transfer. As we have never observed better pregnancy rates in frozen embryo transfers, we don’t share the policies of freezing all the embryos in all cycles (offered by some clinics). In our opinion, the impact of high levels of estrogens, which we sometimes get during IVF, is not enough to impair the implantation rates. We do not want to manipulate the embryos if it is not strictly necessary. As long as there is no high risk of hyperstimulation syndrome, we still carry out fresh embryo transfers in IVF with very good results.
Nowadays, success rates with fresh embryos or frozen embryos are pretty much the same when we speak about blastocysts. There is emerging data saying that those are consistent results.
Therefore, what we tend to do many times is to use frozen embryos instead of fresh embryos. On the other hand, especially when we’re doing IVF with our own eggs, one of the hypotheses why success rates for frozen embryo transfers are a little better is that all the levels of estradiol are more natural and similar to a natural cycle – even if we are doing a medicated one. That might also impact the expression of some genes that are related to receptivity. Therefore, we should not be afraid of using frozen embryos instead of fresh embryos because nowadays, success rates in terms of pregnancies are pretty much the same.
Thanks to vitrification, the technique that we nowadays use to freeze the embryos, the survival rate of the embryos (when you are working in a good lab and a good clinic) is usually more than 95-98%. It means that most of the embryos make it to the thawing process. Obviously, the criteria that are used to decide, which embryos are worth being frozen, are very strict. It maximizes the chances that those embryos can survive the thawing process and give a pregnancy.
Some years ago, vitrification did not exist, and the way of freezing embryos was very slow and harmful to the embryos. When we thawed them, their quality was lost or decreased. That’s why a few years ago, it was better to do a fresh embryo transfer rather than a frozen one.
Nowadays, with the vitrification process, things have changed. Vitrification is a fast method of freezing the embryos that maintain their quality. So when we refreeze the embryos, they are the same as if they were fresh. Thanks to vitrification, we can now transfer either fresh or frozen embryos – with the same success rates.
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