Choosing the best embryo A day 3 embryo with 8 evenly sized cells, few fragments, graded A.
EMBRYO selection does not increase the overall
chance of a baby from all the embryos available, but it may reduce the time to pregnancy by transferring better embryos first. Day of transfer, embryo grading, timelapse imaging (TiMI) and pre-implantation genetic screening (PGT-A) are all ways of selecting embryos.
Day of transfer
An expanding blastocyst (stage 4), with a clear clump of fetal cells (top left) (A), and a dense outer layer of placental cells (A), graded 4AA.
It is only after day 3 that the embryo uses its own genes to drive growth. Only half the embryos picked as the best choice on day 3 turn out to be the best choice on day 5. If you have several fertilised eggs, it makes sense to wait until day 5, when embryos reach the blastocyst stage, to pick the best embryo to transfer. There is no extra cost for blastocyst culture.
A 4AA blastocyst soon after thawing, before transfer. The blastocyst has contracted but will re-expand within a few hours.
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PATHWAY TO A CHILD
What are the benefits of blastocyst culture? • Blastocyst culture tells you more about the potential of your embryos • It offers better selection than appearance on day 3 • Because of these advantages, we now only freeze embryos which reach the blastocyst stage What are the risks? • Though uncommon, it’s possible for good embryos to stop growing in the lab unexpectedly, so there is no embryo to transfer. This is why we transfer embryos on day 2-3 when you have few embryos.
Day 3 grade
Typical appearance
A
7 or 8 cells, even-sized cells, little cellular fragmentation
B
6 or more than 8 cells, some cells uneven or cellular fragmentation
C
Fewer than 6, uneven cells, fragmentation
Blastocyst grade
Typical appearance
A
Many fetal and placental cells
B
Moderate number of fetal and placental cells
C
Few fetal or placental cells
Blastocyst stage
Typical appearance
1-2
Early blastocyst, with small fluid space
3
The fluid space fills the centre of the blastocyst
4
The blastocyst has started to expand its diameter
5-6
Some or all of the blastocyst has hatched out of its embryo shell
