@Peachy- As much as I wish it were true, 3dt does not have anywhere near the same success rate as 5dt. Especially on a per-embryo success scale. Yes, lots and lots of women get pregnant from 3dt- I mean, that was the only available form of IVF for a very long time, and it does definitely work, but the chance of implantation of a blastocyst is more than double that of a 3dt embryo.
With the way an embryo grows- the first few days are based on if fertilization happened correctly and then on the health of the egg alone. So if you have a lot of embryos make it to day three, you have healthy eggs and sperm that are capable of fertilization. At day three, the genetics of the embryo kicks in. This happens around the 6-8 cell mark. From there, the embryo genetics can either thrive or fail. The longer the embryo is kept in the lab, the more that is known about its health. So when the embryos are transferred back at d3, there is no way to know how healthy the embryo actually is.
A day 5 transfer is the ideal transfer date because this is a day that the embryo would actually be in the uterus after natural conception. Placing an embryo into the uterus on day 3 in not the ideal condition for the embryo. The fallopian tubes have a much different blend of nutrients than the uterus and the embryo should still be there at day 3. This is why they move the embryos to a different culture medium on day 4 when growing them to blastocysts. By placing the embryo into the uterus on day 5, the embryo is placed in the correct environment, just prior to implantation, after giving the embryologist the most information possible.
Some of the top IVF doctors in the world are beginning to push to get rid of 3dt saying that if an embryo cannot make it to blastocyst in the lab, there is no way it can make it within the uterus, and that transferring possibly faulty embryos on day 3 is actually unethical and unfair to couples pay OOP for insanely expensive treatments. They say that the lab conditions that we are now able to attain are ideal for embryonic development, and moving an embryo back to the uterus at d3 does not give it a better chance, it only give the clinic an opportunity to charge the client for transfer. Obviously, the clinic makes more money with a 3d embryo transfer than on a failed cycle. However, if an embryo would not have made it to d5 in the lab, there is no way it would make it to d5 in the uterus either.
In ideal conditions only about a half to a third of embryos that make it to day three will be strong enough to make it to blastocyst stage, whether in the lab or the uterus. That means that if you have two embryos sitting in the lab at d3, there is a still a good chance that neither of them is actually strong enough to make it. But by going ahead and transferring the embryos then, the clinic is still able to charge you for the transfer. This is why after a 3dt the clinic still does not freeze the remaining embryos until d5 or d6.
I am not trying to sink anyone ship or make anyone feel bad, but I really do think it is important that we all understand the process we're going through.
Note: There are some clinics who only transfer 3d embryos that have passed the Early Embryo Viability Assessment test, which does a much better job at selecting embryos capable of becoming blastocysts, but this technique is not widely used. Most clinics still use the standard grading system. It's worth asking your clinic if they are able to employ a higher tech method to evaluate the first 3 days of embryo development. The extra cost associated with the test is generally worth the increase in success rate.
Alot has happened, I ended up doing 11 days of stims and on Monday I triggered. While on the phone with the nurse that was telling me what to do, after that was done she proceeds to tell me that we will have to freeze all eggs!! I was absolutely devastated to say the least. She said that my progesterone had risen and was out of sync with my uterus lining. I only had 7 follicles!! So we went for ER on yesterday morning and got 5 eggs. The embryologist called this morning and 3 fertilized! SO now we are hoping and praying that all three make it to day 3 for the freeze. We will be doing a FET next cycle. 
