At Dominion Fertility, we are often asked by IVF patients about the choice between a day 3 and day 5 embryo transfer. Back in 1996 we were doing mainly day 2 embryo transfers. For those not clear on the concept of day 2, 3 or 5 let me step back for a second and explain. In IVF speak, day 0 is the day of the egg collection. This procedure is done under light sedation and has a low rate of complications. In Natural Cycle IVF we almost always retrieve just a single egg since the vast majority of natural cycles result in just one mature follicle with the other follicles failing to grow past 10-11 mm in size. In stimulated IVF cycles we use fertility shots to rescue the extra follicles and usually end up with 10-18 eggs (some women make very few follicles [decreased ovarian reserve] and others make a lot of follicles [PCOS patients]). On the afternoon of day 0 the egg and sperm get to meet each other (usually by injecting a single sperm in each egg - ICSI). On day 1 we expect to see evidence of normal fertilization with a 2 pn egg. The fertilized egg then starts dividing so by day 2 it is 4 cells and by day 3 it is 6-10 cells and by day 5 it is hundreds of cells organized into a hollow ball or blastocyst. Not all beautiful day 3 embryos will continue to grow to blastocyst and not all borderline looking day 3 embryos will stop growing.
So what about day 3 vs day 5? For our stimulated IVF patients it is easy...we always push to day 5. We stopped doing any fresh day 5 transfers and now freeze all embryos at day 5 or 6 for future use in a frozen embryo transfer (FET) cycle. There is very good support for this approach as long as a clinic has a good freezing program (which we do). Also most of our patients elect to pursue genetic testing of their embryos with preimplantation genetic screening (PGS) and this necessitates waiting to day 5 as opposed to performing embryo biopsy on day 3. Day 5 embryo biopsy is very accurate (99%) and does not seem to damage the embryo.
Natural Cycle IVF is a bit more hazy. We started the NC IVF program 10 years ago in 2007. Initially we chose to go to blast on all patients. However, after a few years we spoke with some of our European colleagues who suggested that we consider doing a day 3 transfer initially and then making the move to day 5 if a patient failed to conceive with a day 3 embryo. We have gotten VERY good at culturing the embryos and I really believe that if an embryo fails to grow to day 5 then it was not going to produce a baby if it had been transferred on day 3. Our incubators have gotten a lot better over the years and we now know a lot more about how to feed and grow these embryos than we did back in the early days of IVF when each clinic actually produced its own culture media! Wow, what a difference a few decades make! If an embryo is not as developed as we would expect on day 3 then we also will push to day 5. Some of these will kick it into gear and turn into nice blastocysts and beautiful babies and some will stop growing altogether. Natural Cycle IVF allows us to track that single egg all the way to a baby and this has allowed us as a clinic to offer some unique insight into fertilization and development that few other clinics possess. For example, most clinics discard eggs that do not show definitive signs of fertilization on day 1. In our NC IVF program we have seen these eggs grow to blastocyst and result in healthy babies demonstrating the limits of our understanding of the precise timing of early embryo growth and development.
So we want to do whatever it takes to give our patients the success that they want from our IVF program. We remain innovative and flexible to provide a wide range of options. Rest assured, leaving your embryos in the incubator is not a problem.