FET success rates

[twoboysandcounting]

Hi Dr. Potter- I wondered if you could offer any insight into what factors affect a clinics FET success rates. We have 2 embryos frozen at an out of state clinic. They have excellent fresh success rates (60% live birth, 1/2 of which are multiples) however their FET rates are very poor (30%). They use vitrification. We are wondering if it would be better to do our FET at a local clinic that has better fet rates. It seems that the biggest factor affecting success would be the quality of the embryo, however with fresh and frozen rates so far apart, there must be other factors unique to the fet that is bringing their frozen rate down. In your experience, what would these factors likely be, and would cycling at a local clinic with better FET rates increase the odds if success with our 2 frozen embryos? Thanks for your help!

[Dr. Potter]

Hi Dr. Potter- I wondered if you could offer any insight into what factors affect a clinics FET success rates. We have 2 embryos frozen at an out of state clinic. They have excellent fresh success rates (60% live birth, 1/2 of which are multiples) however their FET rates are very poor (30%). They use vitrification. We are wondering if it would be better to do our FET at a local clinic that has better fet rates. It seems that the biggest factor affecting success would be the quality of the embryo, however with fresh and frozen rates so far apart, there must be other factors unique to the fet that is bringing their frozen rate down. In your experience, what would these factors likely be, and would cycling at a local clinic with better FET rates increase the odds if success with our 2 frozen embryos? Thanks for your help!

This is such a great question! There are many factors that go into FET success rates. One of the biggest is patient selection. A clinic that is good at 'freezing' and 'thawing' should be able to successfully bring embryos back to their former state. If you have a crumby embryos and 'freeze' them, you are not going to have a better embryos after 'thawing'. The reason for the " ' " marks is that the best clinics are not 'freezing' anymore but are using vitrification like your local clinic is. This process involves rapidly taking the temperature from slightly below freezing to minus 196 degrees celsius (-320 degrees Fahrenheit) rapidly, essentially increasing the viscosity of the liquid so that it becomes solid without the crystal formation of freezing. The problem is that this process has a steep learning curve and is highly dependent on timing and rhythm of the technician. If the embryos are not incubated in the different concentrations of cryoprotectant for the optimal amount of time, the embryos could be damaged. If damage was done to the embryos, it is done during the vitrification rather than the warming. I would rather leave the embryos where they were frozen under these circumstances. At larger centers, the process is more standardized and more likely to be transferable between clinics. I hope this all makes sense.