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. It happens inside the embryology laboratory and requires for the scientific personnel to handle living cells.

It has been said that the embryology laboratory is a surrogate environment (in vitro) resembling the environment provided to the cells by the uterus inside the body (in vivo).

After the egg retrieval and subsequent fertilization with the sperm, the cell will start dividing. It is a process that takes a few hours and guide the embryologist on how things are happening according to the morphology of the cell, the on-time division, normality of the cells dividing, and the degree of fragmentation observed. With this information each cell with receive a grade and the selection criteria will be based on how well the cell did from the very beginning until a few hours before the embryo transfer.

It is a process that has been shown to increase the chances to select the embryo with the highest likelihood to implant and produce a healthy pregnancy.

The day of the egg retrieval the embryologist usually explains to the patient how many eggs were collected and how they look. They day of fertilization (24 hours after the egg retrieval) the embryologist usually contacts the patient to let them know about the fertilization. The information is usually focused on how many of the collected eggs fertilized. Then two days later the embryologist can discuss about the division of the embryos and the quality the have.

From the very beginning these cells have been graded and checked to improve the chances of choosing the right ones. It can be a tough job when all of them do very well, or when they are all showing poor quality.

Normal fertilization:


And this is an example of an abnormal fertilization:


Evolution of the eggs after retrieval:


How to grade them?

Based on their division and behaviour from day 0 (day of egg retrieval) until day 3-5. Also considering the sperm quality and parameters of the response of the patient to the hormones, medical history, endometrial lining, and maternal age.


As a fertility patient it is advisable you establish a trust relationship with your scientific team. They will be in charge of your little cells and to provide you with information on what’s happening. In some cases the communication is through your physician, and some other times you will be able to speak directly to the scientific team.


These tiny, microscopic beings, capable of behaving and giving us hope have been changing patterns of how medicine has been working. They are a clear sample on how life can manifest and open the doors to new horizons. These small cells divide until a full-grown human forms.

Medicine understand a lot about the evolution and development of the fetus inside the womb, but still a long way in regards to the understanding of life from the very beginning.

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