By Andrea Rodrigo BSc, MSc (embryologist).
Last Update: 07/12/2016

In every in vitro fertilization procedure, an excess number of embryos is created in order for the patients to see the likelihood of having high-quality embryos increased, and therefore reaching a higher pregnancy success rate.

This is the reason why many couples end up having a high number of embryos stored in a bank. While some couples prefer to keep them for later use, others may never use it in the end. So, what could be the fate of these spare embryos?

Fate of unused embryos

Those embryos that remain unused after an IVF embryo transfer to the maternal uterus are usually stored via embryo vitrification. In the Czech Republic, the fate of supernumerary embryos could be:

  • Use in prospective fertility treatments carried out by the genetic parents
  • Donation to another couple for reproductive purposes
  • Donation for human stem cell research projects

When a couple makes the decision of donating their embryos, either for the reproductive purposes of another couple or for stem cell research, they must sign a specific consent allowing the fate they have chosen for their embryos. By doing this, they wave their rights and duties over these embryos.

If they decide to donate them for reproductive purposes, the embryos will become property of the receiving couple, whose members are the ones carrying out what is known as embryo adoption.

Reasons for adopting embryos

Couples who find themselves unable to undergo a fertility treatment using their own gametes can can find a solution by moving on to embryo adoption or gamete donation.

Embryo adoption is generally indicated in cases where none of the members of the couple can use their own gametes, and also for single women and same-sex couples presenting poor-quality embryos, repeated implantation failure, recurrent pregnancy loss, and in case there exists a genetic alteration in one of the gametes.

An advantage of embryo adoption is that it helps reduce the duration of the treatment, since it just involves three steps: preparation of the endometrium, embryo thawing, and finally embryo transfer. This way, we can skip the following phases: fertilization, embryo culture, and embryo selection for the transfer.

A second advantage of embryo adoption is the cost of the treatment, as generally it is considerably lower than that of IVF using donated embryos.

Endometrial preparation

The only thing the recipient of donated embryos has to do is preparing her endometrium so that the embryos are able to implant. To that end, she has to take medications that help stimulate endometrial development. Progesterone is the most common fertility drug administered in these cases, either through oral, vaginal, or patch route.

In order for the embryos to be able to attach, the endometrium has to reach a thickness of around 7-10 mm, as well as a triple line pattern, which will be checked through ultrasonography.

Thus, the gynecologist will monitor the cycle through regular ultrasound scans in order to see how the endometrium is growing, and taking that into account, deciding on the most appropriate date for the transfer.

The success rate of embryo adoption will depend mainly on the quality of the oocytes and sperm the embryos were created with, as the embryo donors had to resort to fertility care as well.

If one of the gametes from which the adopted embryos were created came from a donor, embryo quality would be better, and therefore the chances of success higher.

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Authors and contributors

 Andrea Rodrigo
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information