The Association for the Study of Reproductive Biology (Asociación para el Estudio de la Biología de la Reproducción - ASEBIR) has been charged with establishing morphological criteria for classifying embryos. In this way, all Spanish assisted reproduction centres take into account the same characteristics to establish the category of embryos developed in each treatment.
If, after observing the embryo under a microscope, a high degree of fragmentation, numerous vacuoles and/or cells with several nuclei is detected, the embryo will be considered non-viable for transfer. In addition, the thickness of the zona pellucida is important, since the greater the thickness, the more difficult it will be for the embryo to come out and implant itself in the uterus.
