Having had a fresh embryo transfer in my first pregnancy and a frozen embryo transfer in my second I am interested in whether one is preferential to the other. Traditionally, women undergoing IVF have a fresh embryo transfer for their first attempt and then, if there are a surplus of embryos left, then those can be frozen. This allows the woman a chance to use the frozen embryos for a second pregnancy, like in my case, and also a second attempt at the first pregnancy if unsuccessful with the fresh ET. Additionally, women who are at high risk for ovarian hyperstimulation syndrome (OHSS) during the fresh IVF cycle can freeze all their embryos and do a frozen embryo transfer at a later date.
Previously, many centres had FET success rates that were about 10% less successful than their fresh ET. That has changed due to:
- The frozen embryo transfer pregnancy success rates being influenced by the method of freezing embryos which is far quicker than it used to be.
- Fast freezing that leads to approximately 90% of embryos surviving the thaw process. The survival is because there are minimal ice crystals forming with vitrification and minimal cellular degeneration to the embryo.
- The frozen embryo transfer success rate being influenced by the quality of the embryos frozen. Some IVF centers freeze all the remaining embryos while others will only freeze those of good quality. The better the quality of the embryos at the time of freezing, the better the freeze-thaw success.
- Some IVF centers are doing embryo banking cycles with Preimplantation Genetic Screening (PGS). They biopsy the embryos and test them for genetic abnormalities, and freeze them. Once they have enough genetically normal embryos then they transfer these. This is good for woman with recurrent pregnancy loss or advanced maternal age.
So the evidence suggests that like peas fresh is as good as frozen!