Every day patients ask us which is better for me, a day 3 or a 5 to 6 day blastocyst embryo transfer with in vitro fertilization (IVF)? There is no uniform correct answer for every patient. It depends on many things given your individual situation.
In the early days of IVF it was felt that it was best to get embryos back into the uterus very early in development, and embryos were transferred 1-2 days after egg retrieval. This was because laboratory embryo culture conditions were fairly primitive in those early days, and may not have been great for “growing” embryos outside the body.
Over the years we found that as laboratory culture conditions improved we could grow embryos well in the laboratory for 3 days after egg retrieval, and day 3 embryo transfers were standard for many years. The next breakthrough in the laboratory came when it was discovered that embryos need different nutrients in their environment (culture) for them to grow well in the laboratory after 3 days of growth. With changes in the culture media we found we could support good growth of embryos for 5 or 6 days, to the blastocyst stage of development.
Some embryos that look good under the microscope on the third day of development (and may be chosen for embryo transfer on that day) don’t have the best potential to turn into a live born baby. If those embryos were grown longer in the laboratory to the blastocyst stage they would likely have stopped normal growth before becoming a blastocyst embryo. So embryos that are transferred at the blastocyst stage, overall, have a higher implantation rate (chance to “stick”).
However, it is important to have a good IVF laboratory with good culture conditions to support the growth of embryos to the blastocyst stage. Some labs do not have good experience or success with growing embryos to the blastocyst stage. Generally IVF programs that have confidence in their lab’s culture process feel that if an embryo does not develop to the blastocyst stage in the laboratory it likely would not have resulted in a baby if it had been transferred on day 3 of development.
Most IVF programs feel that blastocyst culture is a reasonable tool to use to select embryos with the best potential in patients who have many good quality embryos, patients having a higher number of good quality embryos on day 3 of development than are prudent to transfer. Generally, in a given patient, fewer embryos are transferred at the blastocyst stage than at the day 3 stage of development. In this way we may get the highest pregnancy rates, and by transferring fewer embryos, lower multiple pregnancy rates with blastocyst embryo transfers,
However in patients who have only one or two embryos that are developing at the normal rate, there may be no advantage of growing the embryos to the blastocyst stage. An embryo that is destined to become a baby likely has the same chance to stick whenever it is implanted. In these situations transferring the embryo back to the uterus after 3 or even as few as 2 days of development is likely just as good, since the laboratory is not likely as good an incubator for embryo growth as your body.
Additional issues under debate in our field include the claim that transferring embryos back into the uterus after 5 days of development is more conducive to embryo implantation, since embryos typically implant in natural conception cycles 5 to 6 after ovulation, and the uterine environment may be better at this time. This claim would support blastocyst embryo transfers. Some studies suggest however that there is a higher rate of identical twins (monozygotic) with blastocyst transfers, and these pregnancies are at higher risk for problems including premature delivery.
The scientific IVF world is working on further techniques to help select the best embryos to transfer, but at the present time they need refinement. For the present time you can see there is no absolute right answer to the question day 3 or blastocyst transfer. However blastocyst embryo transfer is a reasonable technique for selecting embryos with good implantation potential. Your IVF team will guide you based on your individual situation to what we believe is the best way to help you achieve a successful pregnancy.
Dr. Louis Weckstein is a leading Reproductive Endocrinology and Infertility specialist at the Reproductive Science Center of the San Francisco Bay Area, where he has served as the medical and IVF director since 1997. Dr. Weckstein has particular interest and experience in all aspects of IVF, including Egg Donation and fertility in older women. He loves his job and is very appreciative to be able to work in a field where so many couples have been helped to achieve their dream of having a family.
