Understanding IVF embryo grading

For in vitro fertilisation (IVF) to result in a better outcome, transferring the highest quality embryos can be crucial. We use a process called embryo grading to establish the quality of your embryos, assessing their appearance and development, to determine which ones have the best chance of success when transferred.

How is a good embryo determined?

Embryo grading assesses the quality of embryos from day two to day six of development. Embryos can vary in quality and embryologists consider several features to identify those that are more likely to implant in the uterus and lead to a successful pregnancy. These key factors include the number of cells present in the embryos, the rate at which the cells are dividing, the evenness of the cells and the presence of any fragmentation within the cells.

Grading day three embryos

Day two to three embryos, also known as the cleavage stage, refers to the early stages of development. During this phase, the cells within the embryo are dividing, but not growing in size. On day three, embryos are assessed to see if they are on target for development pattern. The quality of the embryo based on cell quality will also be indicated. An embryo which is on target and of good quality may have a greater potential to develop to blastocyst stage.

It is also important to understand that lower graded embryos can lead to a pregnancy, as they are constantly dividing. Other factors such as genetics and uterine conditions can also influence the likelihood of implantation.

Grading day five embryos

From day three to five, embryos develop into a blastocyst, which is typically graded on day five. The grading used on day two to three differs from that used at the blastocyst stage, known as blastocyst grading. Embryos are graded from A to F, with A being top quality and F being lower quality. Embryos graded A-C are considered suitable for freezing. The blastocysts are then transferred to the womb to continue developing.

Why do embryos fail with good grading?

In some cases, high quality embryos can still fail to implant due to various factors. One significant factor includes the timing of the transfer. The uterine lining, or endometrium, is only receptive to the embryo during a short period known as the implantation window. If the embryo is not transferred at the right time, the chances of implantation and a successful pregnancy may decrease.

Genetics can also have an impact on the implantation process. An embryo with any abnormalities is less likely to implant in the uterus, which can lead to a failed transfer or miscarriage.

Furthermore, certain fertility conditions such as endometriosis, fibroids and polyps can negatively affect embryo transfer and the ability to implant correctly. These conditions may cause inflammation, affect blood flow and alter the structure of the uterus, therefore disrupting the transfer process.

Reviewed by Tracey Davey, Clinical Co-ordinator at TFP Nurture Fertility.