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Implantation failures and good quality embryos

Embrión calidad AA

When a couple or woman is undergoing in vitro fertilization or egg donation treatment, one of the most important moments is to achieve the implantation of the embryo in the endometrium. The endometrium is a layer that lines the interior of the uterine cavity and where the embryo attaches to initiate gestation.

The embryos are cultured in the laboratory until they reach the blastocyst stage (5 days). During this process, embryologists analyze them in order to classify them according to their quality. For this, certain parameters are taken into account such as: the number of cells and their symmetry, the type and percentage of cell fragmentation, the rate of division of the embryo, among others. Embryos are classified as A, B, C and D.

  • Embryo A: optimal quality and maximum implantation capacity
  • Embryo B: good quality and implantation capacity
  • Embryo C: medium quality and implantation capacity
  • Embryo D: low quality and implantation capacity

Embryologists preferably choose A or B quality embryos, since they are the most likely to implant and thus achieve the expected pregnancy. On some occasions, good-quality embryos are not obtained and medium-quality embryos may be transferred. The surplus embryos can be vitrified for later attempts or, if the patients decide not to undergo any more treatments, they can be donated to help other couples who need them (embryo donation), provided that certain conditions are met.


Implantation failure is when after three or more cycles in which good-quality embryos have been transferred, pregnancy has not been achieved. In this situation, it is important to determine the cause of the problem in order to solve it and try again, in order to achieve pregnancy as soon as possible.


The most common causes of implantation failure and failure to achieve pregnancy are linked to embryonic and/or uterine causes, although there may be other factors involved. There are cases where other causes come into play such as infertility of unknown origin, causes that are very complicated to diagnose.

An embryonic cause can result in implantation failure with embryos that are apparently of good quality but do not have a correct chromosomal load (they are genetically altered). Also, in this case, it can lead to miscarriage. To avoid this, it is very important to study the karyotype of the couple or the woman and to biopsy the embryo by means of Preimplantation Genetic Diagnosis (PGD).

On the other hand, if the cause is uterine, it may be due to endometrial receptivity not being optimal at the time the embryo transfer was performed. For this, we can analyze whether the endometrium is receptive by means of an endometrial receptivity test (ERA test). In this way, we can freeze the embryos and transfer them at the optimal moment to facilitate implantation.


At Ovoclinic, our success rates are above average due to our continuous innovation and improvement of protocols in the laboratory, in order to achieve our patients’ dreams. Other alternatives to improve embryo selection are long culture until blastocyst (day 5-6 of development) and the use of incubators with time-lapse technology, which allow us to visualize the entire embryonic development without removing the embryos from the incubator. Both methods provide us with more information about embryo development and help us to better choose the embryo to transfer.

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