Embryo transfer is the last step of in vitro fertilization (IVF). The embryo or embryos that have been developed in the laboratory are transferred to the mother's uterus so that implantation can take place.
Sometimes it is necessary to freeze the embryos and postpone the transfer to a later cycle. On the other hand, embryos left over from an IVF cycle are also cryopreserved for use in future attempts.
In these cases, a frozen embryo transfer will be made, which can be done in a natural cycle or a replacement cycle.
Provided below is an index with the 6 points we are going to expand on in this article.
Frozen embryo transfer
One of the most important parameters when performing an embryo transfer that guarantees the success of IVF is the condition of the endometrium.
For embryo implantation to take place, i.e. the union of the embryo with the mother's womb, the endometrium has to be receptive.
The optimal endometrial thickness indicating uterine receptivity is 7-10 mm, in addition to observing a trilateral aspect by ultrasound.
Normally, to achieve a receptive endometrium and do the embryo transfer, assisted reproduction specialists use hormonal drugs in what is known as replacement cycle.
This hormonal mediation is based on estrogens and progesterone, with which it is possible to control the menstrual cycle in an exogenous way and thus increase the probability of pregnancy.
If you are interested in obtaining more detailed information on this subject, you can continue reading here: Preparing the endometrium for embryo transfer.
What is a natural cycle?
The embryo transfer in a natural cycle, unlike the previous case, consists of taking advantage of the normal growth of the endometrium thanks to the effect of endogenous hormones produced by the ovaries.
These endogenous hormones are estrogen, produced in the proliferative phase of the menstrual cycle, and progesterone produced by the corpus luteum in the secretory phase.
In order to make a frozen embryo transfer in a natural cycle, it is necessary to have regular menstrual cycles and normal ovulation.
From day 10 of the menstrual cycle, it is advisable to perform 2 ultrasound checks to evaluate the state of the endometrium and ovulation and then schedule the transfer day.
Normally, the transfer takes place as many days after ovulation as the number of development days the embryo has. For example, if the frozen embryo is a 5-day blastocyst, it will be transferred to the uterus 5 days after ovulation in a natural cycle.
All of the advantages gained by carrying out a natural cycle during an IVF are due to the fact that no hormonal medication is required. We will discuss them below:
- The side effects are minor, even non-existent.
- The treatment is not so emotionally draining, as there is no need to be attentive to the administration of the medication.
- The economic expenditure is much lower as you do not have to buy the hormonal drugs.
- Gynecological check-ups are minor.
- There is no more hormonal medication necessary after embryo transfer.
Despite this, some specialists do tell women to take progesterone after the embryo transfer, even if it took place in a natural cycle.
The natural cycle is not an option for all fertility patients, as some of its disadvantages decrease the probability of success of the treatment. Among them, we find the following:
- Ovarian function and regular menstrual cycles are necessary.
- There is less flexibility in terms of the days to go to the controls and schedule the transfer.
- There is an increased risk of cancellation of the transfer due to early ovulation.
As for the professional experience, Dr. Gorka Barrenetxea tells us that:
the use of natural cycles requires stricter monitoring because that woman's endogenous hormone production must be controlled. When we use exogenously administered estrogens or progesterone we already know the amount we are administering and therefore monitoring is less strict.
We prefer to perform the frozen embryo transfer during a replacement cycle.
FAQs from users
Is the success rate higher for frozen embryo transfers in a natural cycle?
In fact, the transfer of embryos with a natural cycle has the same gestation rate as the preparation by means of a replacement cycle.
The advantage of the natural cycle is that there is almost no need to take medication (the second phase of the cycle should always be reinforced with utrogestin).
On the other hand, its disadvantage is the discomfort, because to do a natural cycle correctly the patient must do an ultrasound at least every two days.
When is a natural cycle cryotransfer indicated?
The main indication for transferring embryos in a natural cycle is implantation failure. When fertility patients have suffered from repeated implantation failures in previous transfers, the natural cycle is one of the most commonly used options.
Read more here: Repeated Implantation Failure - Reasons Why Embryos Don't Implant.
Can egg donation be done in a natural cycle?
Yes, when it comes to making an embryo transfer, it does not matter if the embryos come from your own or donated eggs. As long as the recipient woman has regular menstrual and ovulatory cycles, it is possible to make an embryo transfer in a natural cycle.
However, it is not convenient to make a natural cycle if the transfer is going to be fresh, since it is very complicated to synchronize the donor with the recipient and, therefore, the probability of success would be lower.
As for the treatment of embryo adoption, this can also be done in a natural cycle and, furthermore, these embryos will always be cryopreserved.
What is the success rate of a natural cycle embryo transfer?
The pregnancy rate by transferring frozen embryos in a natural cycle is similar to that obtained in a replacement cycle. The most important thing is to analyze all the factors of each treatment and each patient and, in this way, apply the protocol that can benefit the most in each case.
Suggested for you
The transfer of frozen embryos is an increasingly common practice in fertility clinics. If you want to know in detail how it is done, you can read on here: Frozen Embryo Transfer- How Does It Work?
One of the most important parameters when performing an embryo transfer that guarantees the success of IVF is the condition of the endometrium. The following post may be of interest to you if you are looking for a pregnancy: Tips to Increase Endometrial Thickness.
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FAQs from users: 'Is the success rate higher for frozen embryo transfers in a natural cycle?', 'When is a natural cycle cryotransfer indicated?', 'Can egg donation be done in a natural cycle?' and 'What is the success rate of a natural cycle embryo transfer?'.