As we have discussed in our overview of IVF and blastocyst transfer, we hope to fertilize more eggs than we use, so that we can transfer the strongest embryos in the hope of implantation and pregnancy. If, prior to embryo transfer, there are several viable embryos, you have the option of electing to freeze — cryogenically preserve — these embryos for future IVF procedures or to donate to other parents looking to conceive.
Why are there extra embryos?
IVF and egg donation cycles can often produce more embryos than you may wish to have transferred. In recent years, we have been able to transfer fewer embryos than in the past while maintaining the pregnancy rate and lowering the multiple gestation rate. It is possible to cryopreserve these extra embryos by storing them in liquid nitrogen. The cryopreserved embryos can be thawed and transferred into the uterus at a later date. The first reported pregnancy in humans from frozen embryos was in 1983, with the first birth occurring the following year.
We will let you know around the time of your fresh embryo transfer whether your remaining embryos are of a sufficiently high quality for cryopreservation, which is done on site in our Edison office. If you conceived during the initial IVF or egg donation treatment and then you achieve a frozen embryo transfer pregnancy, you may have a set of twins or triplets born months or years apart!
The implantation rate of the surviving thawed embryos is similar to the fresh embryos. The complexity and the cost of frozen embryo transfer are greatly reduced compared with repeating the full IVF or egg donation treatments. The main emphasis of the process of frozen embryo transfer is on the preparation of endometrial lining and its synchronization to receive and support the frozen-thawed embryos.
The transfer of cryopreserved/thawed embryos consists of:
- Preparation of endometrial lining
- Thawing and culture of cryopreserved embryos
- Transfer of the surviving embryos into the uterus
- Establishment of pregnancy
How will my embryos be frozen?
Many IVF clinics (including ours) are currently doing most of their embryo freezing at the blastocyst stage. There has been a recent trend in the IVF world away from the traditional slow freezing method that has been used since the 1980’s. Vitrification for IVF embryo freezing is becoming a more widely used technology. Vitrification is ultra-rapid IVF embryo freezing instead of the traditional slow freezing process. We started vitrification of blastocysts in our IVF lab in 2008 and have seen excellent post-thaw embryo survival and high pregnancy rates after frozen transfer procedures. There is no increase in birth defects among frozen-thawed embryo pregnancies compared with spontaneous conception pregnancies.