Day 5 & 6 - Assessment of blastocysts

Day 5 & 6 - Assessment of blastocysts

By day five some of your embryos should have developed into blastocysts.  They look very different to embryos; the cells are now starting to specialise into those which will form the baby (the inner cell mass) and those that will form the placenta (the trophectoderm, the outer layer).

The blastocyst will ultimately hatch from the protective ‘shell’ which has surrounded the embryo through its early development. This is called the Zona Pellucida. It is this mass of hatched cells which, once free from its shell, will implant into the lining of your womb and form the pregnancy. 

How do you choose the best embryo for transfer?

The blastocyst is a more advanced development stage, so we know that embryos which form good quality blastocysts have good potential to implant.  Your blastocysts will be graded using a microscope on the morning of day five using a nationally approved blastocyst grading scheme.. We will select the one or two strongest looking ones for transfer.

If your treatment involves the use of Embryoscope time lapse technology, then we do things a little different. Visit our section on Embryoscope to see how it works and what we do with it.

What should I expect?

We will call you before 10:30 on day five to arrange your embryo transfer the same day. Again, you should make sure you are close to the phone at this time.

If there are any remaining good quality blastocysts after the transfer, we will freeze them so that you can use them in a frozen blastocyst transfer if you need to. 

The window of time where blastocyst formation can normally occur is day 5 and day 6 so we will review any embryos which were not suitable for transfer or freezing on day 5 again on day 6 and it may be that we freeze blastocysts on day 6 as well as day 5.