Blastocysts

Blastocoele

The blastocoele is a fluid-filled intercellular cavity which increases its volume during blastocyst expansion. This process eventually leads to hatching, allowing thus the blastocyst to enter into contact with the uterine endometrium and to implant.

Three stages can be described:

1. the blastocoele volume is less than 50% of the volume,
2. the blastocoele is greater than 50% but the blastocyst has not yet expanded, 
3. the blastocoele is greater than the initial volume and the zona pellucida has started thinning.

 

 

Inner cell mass

The inner cell mass (ICM) is a mass of cells inside the blastocoele which will eventually give rise to the definitive structures of the fetus. The number of cells in the ICM and the degree of compaction of these cells changes during blastocyst development. The ICM can contain few or barely not visible cells, few distinguishable but uncompacted cells, may compacted cells.

 

 

Trophectoderm

Also known as trophoblast, the trophectoderm is a single layer of cells tightly associated cell at the periphery of the blastocyst. The trophectoderm may contain very few cells, few still identifiable cells, many cells forming a tight epithelium.

 

 

Parameters of the EQC test

The EQC test will present you several possible answers for the various characteristics of a blastocyst. You can make only one choice. Although you may not be used to grade the blastocysts in your day-to-day activity, grading is a convenient way of communicating blastocyst characteristics both to colleagues and medical staff. In our view, it this is an important parameter to monitor in an External Quality Control scheme.

 

Blastocoele

The blastocoele is a fluid-filled intercellular cavity which increases its volume during blastocyst expansion. This process eventually leads to hatching, allowing thus the blastocyst to enter into contact with the uterine endometrium and to implant.

Parameters	Morphological aspects
Small	the volume of the blastocoele is less than 50% of the total volume
Medium	the volume of the blastocoele is greater than 50% of the total volume
Large	the blastocoele occupies the whole volume inside the zona pellucida and has started expansion, leading to a thinning of the ZP

 

Inner cell mass

The inner cell mass is a mass of cells inside the blastocoele which will eventually give rise to the definitive structures of the fetus. The number of cells in the ICM and the degree of compaction of these cells changes during blastocyst development.

Parameters	Morphological aspects
Many compacted cells	the ICM contains many small compacted cells.
Few poorly compacted	the cells in the ICM are still separated and poorly compacted
Few cells	the ICM contains either few cells or is barely/not visible

 

Trophectoderm

Also known as trophoblast, the trophectoderm is a single layer of cells tightly associated cell at the periphery of the blastocyst.

Parameters	Morphological aspects
Many cells forming a tight epithelium	the trophectoderm appears clearly made of many small cells tightly attached and forming a single layer epithelium
Few poorly attached cells	the trophectoderm is made of identifiable cells
Very few cells	the trophectoderm contains few cells

 

 

Effects of blastocyst morphology on implantation