How we select embryos for transfer

Embryo selection timing: fresh transfers (FT) vs frozen embryo transfers (FET)

For fresh embryo transfers, all embryos are assessed on the morning of day 5, and we select the embryo that is progressing the best at that time. For frozen embryo transfers (FETs), embryos are reviewed and selected the day before the transfer. Information on how we track embryos can be found here.

How do we select embryos for transfer?

Selecting an embryo for transfer, when there is a cohort of embryos to select from, can be a complex process that involves assessing multiple factors, including utilisation of advanced technology. Here’s how we carefully evaluate embryos to choose the embryo for transfer from a cohort:

1. Genetic testing (if performed)

If your embryos have undergone genetic testing, known as Preimplantation Genetic Testing (PGT), the genetic results are weighted above all other embryo selection methods. Embryos with the correct number of chromosomes are considered suitable for transfer, which helps to reduce the risk of miscarriage or genetic conditions related to chromosome issues.  This testing allows us to focus on embryos with the best chance of resulting in a healthy pregnancy. More information on PGT-A results can be found here.

2. Embryo grading system

We assess the embryos based on their appearance using our blastocyst grading system. Embryos typically develop to the blastocyst stage around day 5 or 6 of culture. We assess their degree of expansion (i.e. the number of cells), along with the appearance of two key cell groups: the inner cell mass (ICM) and the trophectoderm (TE). Both the ICM and TE are graded from A to D based on their structure and appearance. As there are several factors that are taken into consideration for embryo grading, we also consider timing of the evaluation when we review the embryos for selection. The grades are only indicative of appearance at the time of assessment and this may change with time. Grade A and B embryos are considered good quality in appearance, and Grade C embryos remain viable and capable of resulting in healthy pregnancies. Grade D embryos are considered non-viable and are not suitable for transfer or freezing.

You can find more information on embryo grading here.

3. Monitoring embryo development using time-lapse imaging and artificial intelligence (AI)

We continuously observe and review embryo development over 5-6 days using a special time-lapse imaging system. Embedded Artificial Intelligence (AI) analyses factors such as the appearance of cells, the timing and pattern of cell divisions, and other key developmental events. AI helps prioritise those with the highest potential for implantation and pregnancy. While AI is a valuable support tool, it has limitations; for example, if an embryo has residual support cells attached or excluded cells, AI scoring may be less reliable. Therefore, embryologists use their expertise assessing the videos and the embryos’ morphological milestones alongside AI and the grading system to make the best possible selection.

Integrating all factors to select the best embryo

All these factors (i.e. genetic testing results, embryo grading, AI scores and embryologist expertise) are carefully combined and taken into consideration when selecting embryos. We compare embryos based on this comprehensive information to identify those with the highest potential for successful implantation and pregnancy. However, it is important to understand that every embryo transferred has the potential to form a pregnancy, even those with lower grading or scores, as embryo development and appearance is not always indicative of its developmental potential.

Preparing the embryo for transfer

Selected embryos are chosen either on the morning of day 5 for fresh transfers or the day before for FETs. On the day of transfer, the frozen embryos are carefully thawed and we expect over 97% of embryos to successfully thaw.  There are rare instances that an embryo may not survive the freeze/thaw process and in this instance, we will thaw another embryo if available and we will inform you.  If there are no other embryos frozen, we will call you to let you know. After warming, the embryos are placed in specialised incubators designed to maintain the ideal environment until the time of transfer.

Enhancing implantation with a quality transfer medium – EmbryoGlue

At Newlife IVF, all embryos are transferred using a medium called EmbryoGlue, which is rich in hyaluronan, a substance found naturally in the uterus. EmbryoGlue is designed to enhance the embryo’s ability to implant into the lining of the uterus. Several studies suggest that EmbryoGlue may improves clinical pregnancy and live birth rates (Heymann et al., 2020; Adeniyi et al., 2021; Tyler et al., 2022; Reed et al., 2022). While these findings are promising, we continuously monitor new research to provide care based on the latest scientific evidence. You can read more on how we give embryo transfer the best chance of success here.

Best scientific practice

At Newlife IVF, we combine all available technology and the expertise of our embryologists to carefully select embryos with the best potential of resulting in a healthy pregnancy. We only transfer embryos that we believe have a chance of success because we know how much every cycle means to you.  Please be reassured that even the final embryo remaining has the potential of achieving a pregnancy.  If you have any questions about the embryo selection process or your specific treatment, please feel free to discuss them with your Newlife IVF team.