you can call me Cheri (or Cherbear).....I know my name is real close to it but whenever I hear cher i always think of Sonny & Cher up on that stage, her flipping her hair and licking her lips...
They typically do either 3 day transfers or 5 day transfers. **Some RE's do 2 or 4 day as well, for certain circumstances, but the general reason for the gap in days is because they don't like to open up the incubator (where the dish is, I honestly don't know what they call it) and disturb the environment, if they can help it. At least that's what I was told.
If the embryos survive until day 5, that's best. It kind of weeds out the great from the good, and from the bad. If you start off with a large amount of embryos, and by day 3 they are going strong, they will typically wait until day 5 because they expect many of them to last.
For example in my situation for IVF #1, we had only 3 embryos. Unless all of them were like WAAY strong (ahead of 'average' growth), they decided on a 3 day transfer. Since we were transferring 2, there was really no reason to wait and "weed out" any embryos. In fact, they said it was best to get them into my uterus because it's the natural environment.
If you take someone with like 10 embryos to start, well at day 3 they might still have all 10, or maybe 8. By day 5, some of those may stop growing. If the embryologist can watch all of them til day 5, then it gives you a better chance of having the strongest ones transferred. I hope that all makes sense.
And just to be clear, a 3 day transfer CAN work. And even the weakest of embryos have lived and become strong healthy babies. So I don't want you to think that if you end up with a 3 day transfer, that it's doomed or anything. For me a 3 day didn't work last time, so I'm just really hoping this next IVF pans out better.