What is a Blastocyst and how is it graded?
An embryo that is approximately five to six days old which consists of 60 to 100 cells. Two cell lineages form; firstly the inner cell mass which develops into the foetus and secondly the trophectoderm which develops into the placenta. Blastocyst Grading System When grading blastocysts, we use the Cornell grading system which includes 3 separate factors:- Firstly there can be a varying degree of expansion from 1 (least expanded) to grade 6 (hatched). The grading of expansion is as such: Grade 1: Early blastocyst; the blastocoel filling more than half the volume of the conceptus, but no expansion in overall size and notable thinning of the zona pellucida (ZP). Grade 2: Blastocyst; the blastocoel fills more than half of the volume of the conceptus with slight expansion in overall size and notable thinning of the ZP Grade 3: Full blastocyst; a blastocoel of more than 50% of the conceptus volume and overall size fully enlarged with a very thin ZP. Grade 4: Hatching blastocyst, the trophect
