How do embryologists select the best embryos?

The procedure of in vitro fertilization is complex and involves several important and necessary steps in order to increase the chances of success. The scientific personnel needs to be prepared for any last minute event that might arise as consequence of dealing with cells. These gametes can show different behaviors at any moment during each hour they spend in the laboratory.

 

It has been said that the embryology laboratory is a surrogate environment resembling the same environment provided to the cells by the uterus inside the body.

 

Once we obtain the eggs and make possible the fertilization with the sperm, in a few hours we will start having consecutive divisions that are crucial to the process of selecting the best embryos. First we need to take into account the fact that 16 to 18 hours after fertilization we need to pay attention to the formation of the pronuclei. Normal fertilization of the egg will show the presence of two pronuclei, not one, three, four, five, and so on. If we observe anything different than two together, symmetrical and centered then we need to suspect something is not right. This is what we should have:

 

 

And this is an example of an abnormal fertilization:

 

 

 

After this time we will observe subsequent divisions each day, starting from the early cleavage stage during the first 24 hours post-fertilisation, and day 2 and 3 embryos (morula) with 2, 4, 6, 8 and 16 cells).

 

 

Now the selection of the embryos is a key factor even for a well-trained embryologist. Involves the selection of the embryo/s that are considered stronger, with high quality and bigger chances of implantation, and the discarding or freezing of the ones that look less likely to succeed.

 

How to select the embryos if we have seen in our practice success with poor/low quality embryos developing into a healthy baby? And we have also seen not successful procedures using very good/high quality embryos? Not an easy task for us.

 

Some might guide for their pure scientific knowledge than a good quality embryo it is likely to succeed rather than a slow, poor quality one. Some might use their embryologic instinct of using the embryo they considered to be stronger based on some of their qualities like good timing during fertilization and divisions, low fragmentation (rupture of the cells), cell symmetry, good zona pellucida, etc. There may be several factors to consider scientifically speaking. Also clinically it is important to judge the quality of the endometrium and the response of the embryo receptor to the treatment given to prepare for the embryo transfer...Continue reading

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