The vital element of the in vitro programme is incubation and then the detailed assessment of embryos’ morphology (structure). On the basis of observations and conclusions of experienced embryologists, decisions are taken relating, among others, to which embryos should be administered to the woman during the transfer. In the course of in vitro programme the patients are informed how their embryos develop, and talk with the physicians about further steps. Therefore it is worth paying some attention to the basics of the assessment of blastocyst stage embryos.
After 4 days following the oocyte fertilisation the embryo reaches the stage of the so called morula. Most often it looks like a solid cell mass, therefore it is difficult to assess the precise number of the cells themselves. On the 5th day of the culture the embryo in the in vitro laboratory reaches the most advanced stage of development – blastocyst stage. The cells in the embryo are then properly organised forming the outer layer called the trophoblast (later placenta), and the inner cell mass also known as the embryoblast (embryo).
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embryoblast trophoblast blastocyst cavity |
The embryologists examine the cells of the embryo and assess them, and write down their observations using figures and letters. While classifying the blastocysts with the use of the blastocyst scoring system developed by Dr. David Gardner, embryologists use the following:
figure (1 – 6) – determining the embryo’s expansion grade:
1 – Blastocoel cavity less than half the volume of the embryo
2 – Blastocoel cavity more than half the volume of the embryo
3 – Full blastocyst, cavity completely filling the embryo
4 – Expanded blastocyst, cavity larger than the embryo, with thinning of the shell
5 – Hatching out of the shell
6 – Hatched out of the shell
first letter (A,B,C), determining the quality of the embryoblast (ICM, inner cell mass quality)
A – Many cells, tightly packed
B – Several cells, loosely grouped
C – Very few cells
second letter (A,B,C), determining the quality of the trophoblast (TE, trophectoderm quality)
A – Many cells, forming a cohesive layer
B – Few cells, forming a loose epithelium
C – Very few large cells
The morphological assessment of blastocysts is not always consistent with clinical results. In other words, it may happen that the transfer of morphologically best embryos will not result in pregnancy, while administering embryos with poorer morphology finally leads to the birth of the longed-for, healthy baby. Here it is worth trusting the opinion of experienced embryologists who will discuss the situation with You and advise what decision can be taken.
