Skip to main content

Southlake Style

Choosing the Best Embryos

Mar 11, 2013 10:10AM ● By tina

Day 5 development of embryos are the preferred day for embryo transfer as it gives a better selection and higher pregnancy rates for patients

Sponsored by Fertility Specialists of Texas

Written by Dr. Carlos Guerrero, Ph.D., HCLD, ELD

How does an embryologist select the best embryos for transfer?    

This is a question that I am routinely asked by patients undergoing IVF treatment. If an embryologist has 10 embryos from a patient how do we know which one will be the strong one with a high potential to implant and ultimately become a baby? To the untrained eye, embryos will look very similar to each other. However, each embryo displays specific morphological criteria that will allow us to distinguish the ones that are developing the best. This is why a very experienced embryologist is paramount for a successful IVF treatment cycle.

In many ways, IVF is like packing many months of trying to conceive into one cycle, because of the many embryos that often result, but it increases the probability of success by selecting the best embryo(s) from the group to be replaced. 

There are two possible embryonic stages for embryo transfer, one at the cleavage stage and one at the blastocyst stage. At the cleavage stage, the embryos are on either day 2 or day 3 of development in the laboratory after the egg retrieval procedure. These embryos will have approximately 4-cells on day 2 or 8-cells on day 3. Embryos at these stages are more difficult to select between each other, as they look very similar. We use criteria such as the number of cells, the size of the cells and the amount of fragments inside the embryo to select the potentially best one. However, embryos at this stage exhibiting high quality traits don’t necessarily continue developing. There is a process called embryonic activation that occurs around day 3 of development where the embryo actually starts producing its own proteins for further development so if there is any problem with the egg or sperm that produced that embryo it will manifest after day 3 and the embryo will stop developing. Usually, about 60-70% of day 3 embryos will continue developing to the blastocyst stage in world class IVF laboratories. Laboratories with high quality embryo culture conditions will only transfer day 2 or day 3 embryos when all the embryos produced by a patient will be transferred. In this case, if the patient only has 2 embryos they will be transferred regardless of quality so the day of transfer won’t matter as we are not selecting any embryos.

Improved laboratory conditions have allowed us to grow embryos to day 5 of development called the blastocyst stage. This is the preferred day for embryo transfer at Fertility Specialists of Texas’ laboratory, as it will give us a much better selection of the embryos and provide our patients with higher pregnancy rates. Embryos at this stage will have a different more complex morphology than embryos at the cleavage stage. Blastocysts have a fluid filled cavity where we will find a compact mass of cells called the inner cell mass. This mass of cells is what will become the baby. Also, we will find a layer of cells forming around the fluid filled cavity called the trophectoderm which will ultimately form the placenta. Evaluating these components of a blastocyst will tell us which of the embryos is truly the best one from a group of embryos.

Our IVF laboratory at Fertility Specialists of Texas has one of the best embryo culture conditions allowing us to produce high quality day 5 blastocysts. This is one of the reasons we provide our patients with one of the highest pregnancy rates in the nation.

About Dr. Guerrero:

Dr. Guerrero is originally from Colombia, South America. He is a graduate of Louisiana State University, where he received his Ph.D. degree in Reproductive Physiology with emphasis in Embryology. Prior to joining Fertility Specialists of Texas, Dr. Guerrero was a Senior Embryologist and Head of Research and Development at the THR Presbyterian-Harris Methodist ARTS Program in Dallas-Fort Worth,TX .He is board certified in Human Clinical Andrology and Embryology and is a High Complexity Clinical Laboratory Director and In Vitro Fertilization Laboratory Director by the American Board of Bioanalysis.