Day 3 versus Day 5
The ability of growing an embryo to the blastocyst stage (Day 5 or 6 of development) in the laboratory has been an important breakthrough for in vitro fertilization (IVF) that maximizes pregnancy rates while minimizing the risk of multiple pregnancy. By growing embryos beyond the traditional three days, the embryology team can determine, with greater certainty, which embryos are really the “best” in terms of their potential for implantation. As a result, blastocyst culture makes it possible for the embryologist to select the best one or two blastocysts for embryo transfer instead of the usual two to three which are chosen on Day 3 of development. This opportunity reduces the chances of having a multiple pregnancy. It is our goal to continually improve IVF success rates while minimizing the risks. This can only be accomplished through steady improvements of both clinical and laboratory techniques such as blastocyst culture.
Blastocyst Culture and Transfer
In the past, embryos have been traditionally transferred to the uterus on the second or third day of development after retrieval, fertilization, and initial embryo cell division. The rationale for this protocol is to strike a balance between maximizing the degree of embryo selection available through culture and growth in the IVF Lab versus minimizing the exposure of the embryos to culture media which, prior to scientific advancements, could only sustain growth for 2-3 days. However, current formulations of culture media better mimic the natural environment and take into account the changing needs of the developing embryo in vitro.
The benefit of growing an embryo to blastocyst stems from the advanced development of the cells within the embryo. We know that after five days of growth, the cells of a normal healthy embryo will have divided several times and certain types of cells will take on certain functions. Embryos that survive and grow to this stage of development, called the blastocyst, are more likely to be strong and healthy, and thus have a better chance of implantation. Several factors may affect whether an embryo survives and grows to this stage:
- The inherent health of an embryo will determine its ability to continuously grow and divide. While many of the mature eggs may initially fertilize, only a few will continually divide and progress to the four-cell stage on Day 2 of culture, and only a percentage of these will make it to the eight-cell stage on Day 3 of culture. In general, only the heartiest of the embryos will eventually develop into blastocysts.
- A second important variable affecting growth of embryos in the laboratory is the culture media and system. This is one of the factors that distinguishes one fertility center from another. Researchers have now developed new culture solutions designed to nourish the demanding blastocysts. These solutions provide the essential nutrients that give the embryos every chance to reach there full inherent potential. While many of these are commercially available, every lab adjusts their own system including relative pH, amount of humidity, amount of proteins and amino acids which bathe the developing embryos. This fine tuned approach maximizes the blastocysts quality and chance of implantation.
- Lastly, the experience and expertise of the laboratory embryologists is critical to the success of a fertility program in growing high quality blastocysts and achieving a high pregnancy rate. Without this element, even the best patient candidate may end up with a compromised cycle and suboptimal chances of success. Advanced Fertility Care’s success in this area is evidenced by our consistently high success rates within the top 1% in the country, with over 80% of our patients undergoing a blastocyst transfer. It is this dedication and commitment to excellence that provides our patients with the best opportunity to build their families.
What About Day 4 Embryo Transfers?
At Advanced Fertility Care, in Phoenix AZ, Mesa AZ, and Scottsdale AZ, we have had patients ask us about Day 4 embryo transfers. There is a large fertility clinic in town that advertises Day 4 embryo transfers as the next fertility breakthrough. Unfortunately, there is no scientific evidence supported by the American Society for Reproductive Medicine or any world scientific board that supports this practice or claim. In fact, scientific research has shown that attempting to select “good-looking” morula embryos on day four does not correlate with pregnancy success.
The best way for a patient to determine if this claim makes sense would be to examine pregnancy success rates. If Day 4 embryo transfers were the new breakthrough, the clinics success rates for IVF doing Day 4 embryo transfers should be at least at or better than the national average. We have examined and judged the success rates from Day 4 embryo transfers rates to be far below our standards and far below the national average rates. We encourage all patients to educate themselves on success rates before selecting a clinic. For more information on success rates and links to the Centers for Disease Control, please visit our Other Links page.