When we perform an In Vitro Fertilization (IVF) or ICSI cycle, it is possible to obtain more good quality embryos than necessary for immediate transfer to the uterus. In these cases, the surplus embryos are cryopreserved, allowing their use in future cycles without the need to perform a new ovarian stimulation.
Cryopreserved embryo cycle
What is cryopreservation?
Cryopreservation is a technique that allows embryos to be preserved at extremely low temperatures, ensuring that they remain viable for long periods. This process is carried out by freezing the embryos in liquid nitrogen at a temperature of -196°C, where all cellular functions are stopped without damaging the embryo. Thanks to this technique, the embryos can be kept frozen for years and used in future embryo transfers.
Cycle process with cryopreserved embryos
1.Cryopreservation of supernumerary embryos
Once the embryos are generated in an IVF or ICSI cycle, they are evaluated to select the best quality embryos for immediate transfer to the uterus. Those embryos that are not transferred but are of good quality are frozen for later use. This process is highly controlled, and the embryos undergo an ultra-rapid freezing called vitrification, which prevents the formation of ice crystals that could damage them.
2. Storage and preservation
Vitrified embryos are stored in liquid nitrogen tanks, where they can remain for many years without losing their viability. According to Spanish legislation, embryos can be cryopreserved during the woman’s entire reproductive period, which means that they can be thawed and used in future cycles when the woman wishes or it is medically indicated.
3. Thawing and cycle preparation
When the patient decides to use her frozen embryos, the next step is thawing. This process is delicate, but current vitrification techniques allow very high survival rates, with embryos maintaining almost the same quality as before they were frozen. Once thawed, the embryos are prepared for transfer to the uterus.
4. Thawed embryo transfer
The transfer cycle with cryopreserved embryos is simpler than a complete IVF cycle, since it does not require ovarian stimulation or egg retrieval. The woman’s uterus is prepared by a hormonal treatment that ensures that the endometrium is in the best conditions for implantation. This treatment usually includes estrogen and progesterone, which help the uterine lining to be thick and receptive enough to receive the embryos. Once the endometrium is prepared, the thawed embryos are transferred in a manner similar to a fresh IVF cycle, using a very fine cannula in a painless, outpatient procedure.
Advantages of using cryopreserved embryos
1. No new ovarian stimulation is required:
By using frozen embryos, it is not necessary to undergo the process of ovarian stimulation and oocyte retrieval again, which reduces the medical intervention and avoids the risks associated with this procedure. In addition, the cost of the treatment is considerably lower compared to a complete IVF cycle.
2. Greater flexibility in family planning:
Embryo cryopreservation allows women and couples to plan their fertility more flexibly, as they can choose to transfer embryos at a time that is best for them. This is especially useful for women who wish to space the births of their children or who need to delay childbearing for personal or medical reasons.
3. High success rates with cryopreserved embryos:
Although success rates for cycles with thawed embryos may be slightly lower than those with fresh embryos, vitrification techniques have significantly improved results in recent years. Currently, gestation rates with thawed embryos are very comparable to those of fresh embryo transfer cycles.
Legal and ethical considerations
In Spain, embryo cryopreservation is regulated by the Assisted Reproduction Law, which establishes that embryos can be kept frozen during the woman’s entire reproductive period. Couples or women have several options regarding the destination of the embryos they do not use:
– Preserve them for future use.
– Donate them to other couples in need.
– Donate them for scientific research.
– Request its destruction.
The decision on the fate of frozen embryos should be made in an informed manner and with appropriate medical and ethical advice.
Emotional aspects
The use of cryopreserved embryos can be emotionally charged, as it involves making decisions about the future of unused embryos. Some couples or women find peace of mind in knowing that they have frozen embryos for future pregnancy opportunities, while others may feel uncertain about what to do with them if they no longer wish to have children. At IREMA, we offer psychological support and counseling to help our patients make the best decisions for their personal and family situation.
