What stage and grade of embryos can be frozen?
Embryos can be frozen at various stages and grades, depending on the specific protocols and preferences of the fertility clinic or reproductive specialist involved
Embryos can be frozen at various stages and grades, depending on the specific protocols and preferences of the fertility clinic or reproductive specialist involved. Generally, the two most common stages of embryo development for freezing are the cleavage stage and the blastocyst stage.
1. Cleavage stage embryos: Cleavage stage embryos typically consist of 2 to 8 cells. They are usually frozen on day 2 or day 3 after fertilization, before they develop into blastocysts. The quality and grade of the cleavage stage embryos play a crucial role in determining their suitability for freezing. The grading system used may vary between clinics, but it typically takes into account factors such as cell number, cell symmetry, and fragmentation.
2. Blastocyst stage embryos: Blastocyst stage embryos are more developed, typically around five to seven days after fertilization. At this stage, the embryo has divided into two distinct cell types: the inner cell mass (which becomes the fetus) and the trophectoderm (which becomes the placenta). Blastocyst freezing allows for better selection and higher chances of successful implantation during later transfer cycles. The quality of blastocysts can be assessed based on criteria such as expansion (the degree of cavity formation), hatching (the emergence of the trophectoderm), and inner cell mass morphology.
It is important to note that not all embryos are suitable for freezing, regardless of their stage. Embryos with severe chromosomal abnormalities or poor quality may not survive the freezing and thawing process successfully. Each fertility clinic has specific guidelines and criteria for determining which embryos can be frozen, and these decisions are made on a case-by-case basis in consultation with the patients.
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