Why can an embryo stop developing?

Any IVF protocol always has three main characters: a woman, a man and their embryo. And the chance to see the coveted two stripes on the test equally depends on the health and well-being of all three. Let's discuss the embryo in more detail to understand why it can stop developing.

Two cells are involved in fertilization, i.e., an oocyte (egg) and spermatozoa. Each carries a half set of chromosomes, so combining them creates a new organism with 46 chromosomes. Further embryo development is affected by both cells' genetic composition, development potential and ability.

While cells grow and develop in the laboratory, embryologists evaluate their division, structure and appearance. But unfortunately, experts cannot predict which embryo will lead to pregnancy and which will not. They can only describe each specific embryo based on its appearance and development history, nothing more.

It happens so that outwardly an embryo is neither very beautiful (from the point of view of embryologists) nor evenly divided. Experts monitor this indicator in the embryo cells at the division stage – blastomeres. Or embryo fragmentation was revealed, i.e., cytoplasm fragments, presumably not carrying genetic information, which can be separated from cells during division and incorporated back. The number of such fragments can vary greatly. Usually, embryologists estimate the degree of embryo fragmentation as a percentage. And such an “ugly duckling” has every chance of becoming a beautiful blastocyst (embryo on the fifth day of development).

On the contrary, sometimes a morula (an embryo stage on the fourth day of development), which divides well and correctly on the first four days, does not reach the blastocyst stage on the fifth day or has signs of degeneration.

It is pretty difficult to predict such moments in advance, but it is known that the problem of embryo development failure always resides in genetics.