Let me explain.
When you have your eggs retrieved, they are immediately fertilized (unless you’re banking them for a later date because maybe you’re undergoing chemo, or say you’re 35 and there’s no prince in sight).
Day 0 is retrieval, day 1 you hear how many fertilized, and then they are off to grow in a Petri dish for five days. At this point you have a choice to make – though you would have likely made it beforehand – but the choice is to either
1. Transfer (think: implant) a “fresh embryo,” so 6 days after retrieval you pull one from the Petri dish and stick it in, and freeze any extras, or
2. Biopsy and freeze all day 5 embryos. Then you wait 2 weeks for results of the chromosome screening, and then wait two cycles, then go back, and they pull one embryo out of the deep freeze, thaw it, and transfer (think: implant) it back inside.
Why do one, or the other?
Fresh transfers are more common for younger women who on the whole have better egg quality and more eggs with correct chromosome counts. Their reason for not getting pregnant is less likely to be bad chromosome counts. It is more likely something else. So the screening is less necessary. Also, 2% of embryos die in the freeze-thaw process. So, say on day 5 you only have one viable embryo, and you’re 35, you may as well just stick it in and hope for the best. Me, at 41, had one viable embryo on day 5 but chose not to just stick it in, because there’s a 70% chance it would be chromosally abnormal – which is what it ended up being. So, why go through all that for a 70% chance of miscarriage – no thanks.
All that said, I just spoke with a friend who did 2 rounds of fresh transfers at 37. They did their retrieval in Spokane, stayed there for five more days post-retrieval, only to hear on day 5 that there were no viable embryos to transfer. She said she and her husband drove back to Missoula both of them crying the whole way. (On her third round they were successful: they went on to have a healthy baby, followed by a second one from that same batch, a few years later. So their kids are the same age, but 4 years apart.)
I am starting at 41 though, and 70% of my eggs are already toast. My main reason for not getting pregnant is just chromosome count. So what we need is Comprehensive Chromosome Screening – CCS. Because CCS testing takes 2 weeks, the window to stick a good one back in has closed, which is why you need to freeze them, and come back for transfer at a later date. So, if you want chromosome screening, you have to freeze.
Note that CCS is chromosome screening. It is not genetic screening. Chromosome screening only screens for the right and wrong number of chromosomes – 23 pairs.
If you want genetic screening, for common inherited diseases, like Cystic Fibrosis, then you get PGS – Pre-Implantation Genetic Screening. That test screens the genes on the chromosomes for things you might not want. Yeah, different test. Different problem. Different blog post.
So: Fresh, if you think your chromosome counts are likely to be good, Frozen if you think they’re not, and Frozen if you are doing Fresh and have leftovers you want to save for a later date.