There has been a lot of speculation about certain merits of fertility rates. There is even some discussion about its impact on the economy.
Sometimes, performing delayed embryo transfers allows us to improve endometrial receptivity and increase the pregnancy rate. Sometimes, when we perform an IVF-ICSI cycle, either for medical reasons or due to a personal choice, we decide that delayed transfer is the best option.
But what does this process consist of? What are its benefits? In which cases is it advisable? You will have to ask your fertility clinic for more information, but the following guidelines can serve as a starting point.
What are deferred transfer fertility treatments?
There are a lot more people interested in fertility and surrogate treatments these days. One of the most overlooked is deferred transfer.
A deferred transfer is the transfer of vitrified embryos after they have been obtained in an in vitro fertilization (IVF) cycle, in order to transfer them to the mother’s uterus in the future, either for medical or personal reasons.
Until recently, it was believed that this type of transfer was not as effective and that, therefore, the pregnancy rate was lower. This belief could be explained by the old methods of slow freezing. This technique induced the formation of crystals inside the cells, with a more negative impact on those containing a higher percentage of water in their composition – oocytes and embryos – reducing survival rates after devitrification.
At present, with the improvements in culture media, the use of cryoprotective substances and the new methods of embryo vitrification, in which the procedure is performed ultra-fast, we manage to avoid the formation of ice crystals inside the embryo; thus, the possible damage to the embryo is much lower and, consequently, its survival after thawing is higher, exceeding 90-95%.
The new vitrification method is usually performed on days 5 or 6, when our embryos are at the blastocyst stage, the best time according to biologists and doctors to perform the embryo transfer. This moment is the most appropriate because, since the embryos are of better quality, they have a higher survival rate. Also, embryo vitrification is not associated with an increase in malformations compared to the general population.
Indications for delayed transfer
Delayed transfer is indicated on those occasions in which performing embryo transfer in the current cycle would be detrimental to the patient or could decrease the pregnancy rate. Among these cases we find:
- Patients who present ovarian hyperstimulation after responding excessively to medication, and for whom embryo transfer at that time, and a subsequent pregnancy, would worsen the situation.
- Women with elevated progesterone levels on the day of Ovitrelle administration. It has been demonstrated that progesterone levels > 1ng/ml negatively influence implantation rates as it indicates that the endometrium and the embryo to be transferred are not synchronized. It usually occurs in women older than 38 years in which sometimes there is a premature LH peak.
- Cycles of embryo accumulation for PGT. The result of the biopsy is not obtained immediately, so we must vitrify the embryos until we have the definitive report.
- Cases of repeated miscarriages or implantation failure. Cycles in which we perform endometrial receptivity studies prior to the transfer. In this way we will perform the embryo transfer at the moment when the implantation window is in the receptive period.
- In addition to these indications, delayed embryo transfers can also be performed if the patient wishes.
Process for transferring frozen embryos
Sometimes, it is convenient not to transfer the embryos in that same cycle and to freeze them for transfer in a later cycle. This will allow us to improve endometrial receptivity and increase the pregnancy rate.
In this sense, there are two ways to achieve this endometrial preparation: natural cycle transfer and transfer in stimulated cycle.
Natural Cycle Transfer
It is performed at the most appropriate biological moment after ovulation. Natural cycle embryo transfer is indicated in patients whose menstrual cycles are regular.
This treatment allows us to dispense with hormonal medication, which considerably reduces costs and gives access to treatment to patients who are contraindicated for estrogen treatment.
However, this technique requires greater flexibility on the part of the patient to carry out cycle controls and presents a greater risk of cancellation due to early ovulation.
Transfer in stimulated cycle
The preparation of the cycle is carried out with the help of drugs (estrogens) to simulate the uterine behavior performed by nature. The administration of these estrogens can be oral or transdermal.
The greatest advantage of the stimulated cycle is the flexibility it offers the patient, both for ultrasound controls and for scheduling the transfer without affecting implantation.
However, the stimulated cycle transfer requires a greater administration of medication and, consequently, increases the economic cost.
Success of delayed transfer
The probability of achieving pregnancy in a cycle with frozen embryos depends, to a large extent, on the quality of the embryos after devitrification and the qualities of the uterus.
Advances in vitrification techniques allow us to perform transfers without decreasing pregnancy rates; either in a first cycle, or of those surplus embryos of good quality that were not transferred in a fresh IVF cycle, thus increasing the cumulative pregnancy rate.
Some studies have been published in which higher pregnancy rates are obtained in cycles of vitrified embryos compared to fresh embryos. This is attributed to the fact that the endometrium is in a more physiological state, without the deleterious effect that the drugs used in ovarian stimulation can have on it.
