Day 3

Embryo quality

Embryo quality is determined by seven different parameters. The main parameters are:

  • the number of cells in the embryo (stage)
  • the respective size of the cells
  • fragmentation
  • the presence of one nucleus in each cell

We assign a global score based on every individual parameter. We distinguish four grade levels:

1 = excellent
2 = good
3 = moderate
4 = poor

Early embryo development

On day 1 the fertilised egg (zygote) goes through its first division. This results in two cells (blastomeres), which are generally equal in size. On day 2 each blastomere divides again into two equal cells, taking the embryo to the 4-cell stage.
If each of the four blastomeres again divides on day three, the 8-cell stage is reached, preferably with cells of equal size. The embryo reaches this stage 68 to 72 hours after the injection or insemination.

Cell divisions are not always perfectly synchronised, so we also observe intermediate stages with three cells, five cells or seven cells. We then see blastomeres of different sizes, as cells that have already divided coexist with cells that are yet to divide.

  • In principle, every blastomere has one nucleus.
  • The presence of two nuclei may indicate nuclear division before the cells have started dividing.
  • If there are several nuclei in over half the blastomeres, the embryo is not transferred unless no other embryos are available.

Sometimes we also see fragmented nuclei. This means that the nuclei have fallen apart.
In some embryos, small sections of the blastomeres without a nucleus have become isolated. This phenomenon is known as fragmentation. At a later cell stage, the fragments can be included again by the blastomeres or remain isolated.
Embryos containing too many fragments (over 50% of their volume) are considered grade 4 and are not eligible for transfer.

Necessary quality for embryo biopsy

During an embryo biopsy one or two cells are taken on day 3 for genetic diagnosis. To be eligible for biopsy, an embryo has to be of grade 1, 2 or 3.

It is important that sufficient blastomeres are present in the embryo (at least 6) for the embryo to have enough opportunity to develop further. Preferably one blastomere is removed for the genetic test, but sometimes we need to remove two.

Five common questions about embryology

Why has my embryo transfer been postponed from day 3 to day 5?

If the embryo transfer is postponed from day 3 to day 5, this means that at least four good quality embryos are present. In order to make a better selection, we wait until day 5 to make a final choice of the embryo or embryos showing the best development pattern.

Why am I not getting an embryo transfer?

Only embryos up to grade 3 are eligible for transfer to the uterus. If we do not have any embryos of this quality, we have to cancel your embryo transfer. The embryos may not have divided sufficiently, may have stopped developing or showed too much fragmentation. One medical reason may be that you are experiencing hyperstimulation. Going ahead with an embryo transfer in the current cycle would only make this problem worse, as the embryo will also start to produce hormones during its further development in your body. Your physician will adjust your stimulation plan to avoid hyperstimulation during a possible subsequent attempt. If sufficient good-quality embryos are available, we will freeze them for possible transfer later. In a cycle with thawed embryos, the embryo transfer is not preceded by a (major) stimulation stage, so no hyperstimulation can occur. If we were able to freeze any embryos, we will inform you of the number in a letter.

No fertilisation was observed, so why am I still getting an embryo transfer?

If we only saw one pronucleus in the egg, we may still consider the egg fertilised, because the appearance or disappearance of the pronuclei may have been asynchronous. We may have missed the second pronucleus in our evaluation, which is only a snapshot of a particular moment in time. If the quality of the resulting embryo is sufficient and if no other embryos are available, it can be transferred.Why were more embryos transferred than the number of observed fertilised eggs? Again these are 1PN embryos that are considered as 2PN due to the possible asynchronous appearance or disappearance of the pronuclei.

There were no grade 1, 2 or 3 embryos, so why am I still getting an embryo transfer?

If more than half the embryonic cells are multinucleated, the embryos may be transferred if no other embryos are available.

Why were more embryos used for the embryo biopsy than the number of observed fertilised eggs?

Very exceptionally, a 1PN embryo of sufficient quality can be included in the embryo biopsy. We consider the egg fertilised because we may have missed the second pronucleus in the evaluation (non-synchronised appearance or disappearance of the pronuclei). The genetic diagnosis will prove whether the egg was indeed normally fertilised.

UPDATE 05/01/2024: Renovation works Brussels IVF

To increase the comfort and privacy of its patients, Brussels IVF is renovating its nursing unit (VP03) and the reception desk area at our Andrology Lab.

As part of these renovation works, from 8 January 2024, the reception desk of our Andrology Laboratory and its associated rooms to collect a sperm sample, will be temporarily located on the second floor of Brussels IVF (via route 980).

During your treatment, we guarantee the same quality of care but you might experience a reduced level of comfort due to the temporary location with limited space.
We will make every effort to minimise any inconvenience.

Consult the practical guidelines and the FAQ on the renovation works.