When one starts an in vitro fertilisation (IVF) treatment, one of the most frequent concerns is the number of high quality embryos that can be obtained.
This number is variable and depends on several factors such as the ovarian reserve and gamete quality (egg and sperm). Once the eggs are fertilised, they are considered embryos, which begins after their early division. The embryo division is observed in the IVF laboratory on a daily basis and is key information to determine the embryo quality. The Spanish Association of Reproductive Biology (ASEBIR) establishes a classification according to various observed morphological parameters, which indicate the embryo quality according to their capacity to implant in the womb.
It is quite common to see that embryos from the same cohort (from the same ovarian stimulation) do not have the same development, have slower division or even arrest.
Some studies suggest that embryonic arrest is a consequence of the inability to activate important genes for development in addition to the stress caused by their environment (temperature, humidity, pH, gases, etc.) It also suggests that the arrest requires activation of the embryonic genome. This activation occurs on day 3 of embryo development, hence the importance of observing the embryonic division until the blastocyst stage (day 5 of development) as much as possible. The question of what causes the embryonic arrest remains without a clear answer. One hypothesis points to the oxidative stress that the embryos are exposed to and the quantity and distribution of their cellular components.
However, it should be pointed out that embryo arrest in vitro is a useful biological mechanism to rule out the embryos that do not meet certain quality criteria.
Current studies may shed more light on the causes of arrested embryo development. New technologies such as time lapse monitoring are very useful because they offer us a wealth of helpful information to predict which embryos are most suitable for implantation. Furthermore, various molecular techniques directly relate genetic factors (chromosomal alterations, fragmented sperm DNA …) with poor embryo development.
Therefore, it is very important to perform the necessary previous analyses that help us to get a proper diagnosis and individualized and successful treatment.
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