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Decisions to make about your embryos

Before embryo transfer, there are various decisions that need to be made about your embryos. This page explains the decisions you and your clinic will need to make.

What decisions will my clinic and I need to make about my embryos?

During treatment your clinic will talk to you about various decisions that need to be made regarding your embryos. These include:

  • selecting only the best quality embryo(s) for treatment
  • whether to put one, two or (very rarely) three embryos back in the womb
  • at what stage of development to transfer your embryo(s) back to the womb
  • what to do with any remaining embryos that you don’t use in treatment.

How do clinics decide which embryos are the best quality?

Embryos vary in quality – those that are of the best quality are more likely to implant in the womb and lead to a pregnancy. If you have more than one embryo, your embryologist will use their training and expertise to select the best quality embryos using criteria such as:

  • the number of cells present
  • how fast the cells are dividing
  • whether the cell division is even
  • whether there are any fragments of cells present – this means that some cells have degenerated.

Rarely there may be no good quality embryos and then the doctor and embryologist will need to make a judgement about whether they think any of your embryos can realistically continue to a healthy pregnancy.

If this happens, you could think about donating the embryos for training purposes to allow healthcare professionals to learn about, and practice, the techniques involved in fertility treatment. Speak to your clinic for more information about this.

How do clinics decide how many embryos to put back in the womb?

If you have more than one good quality embryo available, it’s now best practice for most women to have only one embryo put back in the womb and freeze the others (called an elective single embryo transfer or eSET). This is to reduce the chance of you having twins, triplets or more (a multiple birth), which can pose serious risks to the health of both mum and babies, including babies that are more likely to be premature or of low birth weight.

Find out more about the risks of fertility treatment.

In some cases a clinic may decide it’s appropriate for women to have more than one embryo put back. This is typically for older women who are less likely to be successful overall and are therefore less likely to have two embryos successfully implant in the womb.

Are success rates lower for women who have elective single embryo transfers?

For the latest statistics on multiple births, visit our Research and data page.

Bear in mind that sometimes the highest quality embryo is selected for eSET, which can have a slight impact on birth rates.

For most women eSETs are far safer and just as effective as multiple embryo transfers, which is why we recommend them.

When are embryos transferred back to the womb?

Embryos can be transferred to the womb at two different stages of their development.

  • Cleavage stage embryos are selected on day two or three of their development
  • Blastocyst stage embryos are selected on day five of their development. 

In the UK, roughly three quarters of women have a blastocyst transfer and a quarter have a cleavage stage transfer.

What’s the difference between blastocyst and cleavage transfers?

The difference is that because blastocyst embryos have been able to develop for longer in the lab it’s easier for the embryologist to select the embryos that are most likely to implant in the womb. This means that blastocyst transfers tend to have higher birth rates.

However, not all embryos that are left to the blastocyst stage will survive and in some cases a couple could have no embryos available to transfer to the womb. There’s no way of knowing if the embryo had been transferred at the earlier cleavage stage, whether it could have continued to a successful pregnancy.

Why are some women less likely to have blastocyst transfers than others?

Some women or couples may be less likely to have a blastocyst transfer because the embryologist is concerned they’ll end up with very few or no embryos if a lot of the embryos don’t survive to the blastocyst stage.

This includes women who are producing fewer normal healthy eggs and older women and couples with only one or two embryos. Generally you’re more likely to be recommended a blastocyst transfer if you’re a younger women with a good number of embryos

What are some of the new techniques being used to select and transfer embryos?

Your clinic may offer you various add-ons, which they claim can help them to select the best quality embryos or ensure an embryo successfully transfers and implants in the womb. However, The fact is, there is no conclusive evidence that any of the commonly offered add-ons increase the chance of a pregnancy.

The add-ons on offer include:

  • time-lapse imaging
  • embryo glue
  • freeze-all cycles
  • pre-implantation genetic testing for aneuploidy (PGT-A)
  • assisted hatching.

To help you ask the right questions and make the right choices for you, visit our treatment add-ons page to get the latest information about the evidence for each add-on. Our traffic light rating system helps you to easily identify which add-ons have been shown to be effective.

What if I have leftover embryos?

If you have embryos leftover after IVF, they can be frozen for use in future treatment (in case treatment doesn’t work, for example, or to try for a sibling) or donated to research, training or someone else.

Find out more about freezing your embryos.

Review date: 4 September 2025