Blastocyst is the stage of embryonic development. After fertilization, embryo in this stage is raised inside laboratory for 5-6 days.

Cell division will be 80-120 cells. Blastocyst consists of embryoblast or inner cell mass and trophoblast which are going to develop to be fetus and placenta later on. Therefore, we can refer this stage is suitable for the embryo implantation.

Embryo in blastocyst stage is well developed to some extent. We evaluate the quality of embryo to be A B C grade. As it is not every embryo in this stage will pass the standard criteria. Screening once again before the embryo transfer is necessary to do.

Generally, we can say the embryo culture is like pre-screening. Because embryologist will do only until 5 th – 6 th day then transfer to the uterine cavity. No more processes in laboratory as the embryo in this stage will need a lot of nutrients. Otherwise, it is showing that the embryo is suffering from the growth retardation. Therefore, this embryo may not give the high rate of success in pregnancy.

Nowadays, our embryo culture is satisfying because of the knowledge, skill, equipment and medical supplies that we can acquire. If we have a lot of embryos, we will raise them until they reach 5 th – 6 th day. It is the embryo screening before use. Easily compared with marathon running, few people can get the finish line under the requirement. For example: 20 people from 100 may reach the finish line within the arranged time. Therefore, embryos that well develop in this stage prove us that they are healthy and strong enough. So, we will have some potential embryos to select. If we can obtain 5 blastocyst embryos, we will grade them by cell amount, size, sequence and any deficiencies detected from microscope. Which can be done by embryologists.

The Advantage of Embryo in Blastocyst Stage:
1. Finding the embryo with good quality for transferring to the uterine cavity.
Once the embryos have been raised until reaching blastocyst stage, we can say it is the pre-screening. Among several embryos obtained, we also classify them by characteristic using microscope. Then selecting the best one to be transferred back to the uterine cavity. If we choose the most perfect embryo, it will lower the lead time of pregnancy confirmation. As well as reducing the abortion rate. Therefore, women will have more possible achievement in pregnancy.

2. Detecting the chromosomes abnormalities or genetic disorders.
We will take out trophoblast cells from the embryo in blastocyst stage in order to do the genetic testing for 23 pairs of chromosomes. With 99% accuracy rate, screening down’s syndrome in the elderly mom, age is over 35 years, experienced in recurrent miscarriage. Furthermore, we can detect the genetic disorder by using medical technologies for example: severe thalassemia. Therefore, this is helping us to ensure we obtain the perfect embryo without any abnormalities. Especially, screening the embryo’s chromosomes during this period doesn’t affect the pregnancy. As blastocyst will not be damaged from taking out trophoblast cells. While doing the same practice to the embryo that reach only day 3 will bring the negative affect because the cell division of this embryo can be done only 6-8 cells.

The disadvantage of embryo in blastocyst stage may occur in case of few embryos obtained as woman has low egg count. Raising until day 5-6, we will not have any embryos left for transfer to the uterine cavity due to they will be killed or deteriorated.

Therefore, if anyone needs to do the embryo culture for a long period, it is important to consider about the necessity, the adequacy of eggs and embryos, the risk of genetic disorders. For examples: Is mother older or younger than 35 years? or Any additional chromosomes testing? This personal medical information should be advised by the specialist as everyone has different physical conditions individually.

Dr. Poonkiat Punyamitr
Obstetrician and Gynecologist, Infertility Treatment Specialist at Prime Fertility Clinic

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Reference: Prime Fertility Center Co., Ltd.
https://www.primefertilitycenter.com/en/qa-with-dr-poonkiat-the-advantage-of-embryo-in-blastocyst-stage/