Most of the IVF clinics abroad that my patients go to for treatment are doing 5 day transfers for the majority of IVF or donor IVF cycles. There is the occasional clinic that will suggest a 3 day transfer routinely, but most prefer to grow embryos to day 5 blastocyst stage to help them determine which embryos are strongest and most likely to result in a successful pregnancy and overall higher IVF success rates.
Some patients that come to me tell me that their prior IVF clinic liked doing 3 day transfers and told them that they believed in doing 3 day transfers because they felt that embryos would do better in the natural environment of the uterus – in essence that some embryos that might not make it to day 5 in the lab, may be successful in the uterus if transferred on day 3. Other doctors disagree with that philosophy.
I recently came across a very good Q&A article from a US doctor that explains why they are primarily only doing 5 day transfers vs. 3 day transfers, and how and why he felt the theory of 3 day embryos doing better in the uterus is flawed. His explainations are quite thorough and are consistent with what I have heard from other reproductive specialists and embryologists on this subject, so I am happy to share it here:
http://www.sharedjourney.com/articles/3vs5.html