What is embryo transfer?
Embryo transfer takes place after eggs have been collected and fertilised in the laboratory.
Depending on your situation between one and three of the best quality embryos are selected and then transferred to the woman’s womb.
An embryo must successfully attach itself to the wall of the womb for pregnancy to begin.
How does embryo transfer work?
The exact procedure for embryo transfer depends on the clinic you choose. A typical procedure may involve the following:
Step 1. Two to three days after the eggs are fertilised, the best quality embryos are selected to be transferred to your womb.
If you are under the age of 40, one or two embryos can be replaced.
If you are 40 or over, a maximum of three embryos can be used (unless you are using donated eggs, when the maximum is two because these eggs will be from donors who are not older than 35).
If you have good quality embryos, those that are not transferred can be frozen. Some clinics may also offer blastocyst transfer, where embryos are transferred five to six days after fertilisation.
Step 2. The doctor or nurse doing the embryo transfer inserts a speculum into your vagina. This is the same procedure as a cervical smear test where the speculum is used to keep your vagina’s wall apart.
A fine tube (catheter) is passed through the cervix, normally using ultrasound guidance. The embryos are passed down the tube into the womb.
This is normally a pain-free procedure and usually no sedation is necessary, but you may experience a little discomfort because you need a full bladder if ultrasound is used.
Step 3. It is generally recommended that you lead a gentle lifestyle during the few days after embryo transfer.
Step 4. About two weeks after the embryo transfer, you will be given a pregnancy blood test. If it is positive, you will have a scan about two weeks later.
New technique - Metabolomics
Researchers are currently developing a new method of embryo selection – Metabolomics. The method could potentially be used to identify embryos with the best chance of implantation.
Metabolomics involves taking a sample of the fluid (culture media) from the dish an embryo is developing in and testing it for levels of certain molecules (metabolites).
Researchers are establishing which molecules, and levels of these molecules, corresponds to the most viable embryos.
What are the risks of embryo transfer?
There are no significant risks relating to the embryo transfer process itself.
If you have never had a baby or if the canal of the cervix has not been assessed before the in vitro fertilisation (IVF) cycle was started, there can occasionally be difficulties in passing the embryo transfer catheter through the cervix.
While it is possible to stretch the cervical canal at the time of transfer, your specialist might prefer to avoid such interventions at this time.
In extreme cases, your specialist may decide that it is in your best interests to delay the embryo transfer and freeze all suitable embryos until after the cervix has been stretched.
There are significant risks if more than one embryo is transferred: you may want to consider single embryo transfer.
For more information on the problems involved in multiple births, speak to your clinician and see the following information:
What are my chances of getting pregnant after embryo transfer?
Female fertility diminishes with age, so if you are using your own eggs, on average, the younger you are, the higher your chances of success.
In the year 2011 (the year for which the most recent data is available) for women receiving stimulated IVF using fresh embryos created with their own eggs, the percentage of cycles reaching embryo transfer that resulted in a pregnancy (national average) was:
- 40.6% for women aged under 35
- 35.5% for women aged between 35-37
- 28.1% for women aged between 38-39
- 21.2% for women aged between 40-42
- 11.2% for women aged between 43-44
- 3.4% (0/81) for women aged 45 and over
For information on frozen (as opposed to fresh) embryos, see:
What are freeze-all cycles?
Freeze-all cycles involve freezing all the embryos in a cycle and waiting to transfer them at a later date. Some people think that by giving the body time to recover from the fertility drugs it allows your uterus to return to its natural state and your chances of conceiving are higher. At the moment there’s been very little research into freeze-all cycles so there’s no evidence that it leads to higher success rates.
Couples having their first round of IVF treatment are invited to take part in a study into freeze-all cycles. More research may help us to determine whether freeze-all cycles genuinely increase your chances of having a healthy baby, with the potential to help tens of thousands of couples who have fertility treatment each year.
To find out more about the study and how to take part, download the resources below.
Page last updated: 04 August 2014