Embryo grading

Embryo grading is the system embryologists use to describe an embryo's appearance under the microscope at a particular stage of development, most commonly at the blastocyst stage using systems such as the Gardner grading system. Blastocyst grading typically records the degree of expansion, the appearance of the inner cell mass (ICM), which will contribute to the future baby, and the appearance of the trophectoderm (TE), which will contribute to the future placenta. Embryo quality, as described by a grade, reflects what was seen in the laboratory on a specific day and is one piece of information used alongside others, such as genetic testing where performed and clinical history, to help decide which embryo to transfer or freeze first. A higher grade is associated, on average, with a somewhat better chance of implantation across large groups of embryos, but grading does not reliably predict the outcome for any single embryo: embryos described with a lower grade have resulted in healthy pregnancies, and a top-graded embryo does not guarantee one. Grading is a description of appearance, not a judgement on an embryo's potential.

Also known as: Gardner grading, blastocyst grading, inner cell mass, ICM, trophectoderm, TE, embryo quality

Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.