Embryo transfer: 2 - 3 days

During an in vitro fertilisation (IVF) treatment cycle, eggs are removed from the ovaries and mixed with sperm in a dish in the laboratory so that fertilisation can take place. The embryos are then left to develop in the dish. An embryo that has developed for 2 - 3 days after fertilisation is known as a cleavage stage embryo.

This stage embryo is the type most commonly used for IVF in the UK at present. The alternative is to leave the embryo for 5 – 6 days, when it is known as a blastocyst.

How does cleavage stage embryo transfer affect the risk of multiple birth?

When two or more cleavage stage embryos are transferred, it increases the risk of multiple pregnancy and birth for several reasons:

• more than one of the transferred embryos may implant in the womb, leading to the development of more than one baby (non-identical twins or more babies).
• one or more of the transferred embryos may develop into identical twins. A recent study showed that you are 2 to 5 times more likely to become pregnant with identical twins after receiving fertility treatment than after natural conception.

After natural conception, the risk of a multiple pregnancy is quite small, at around 1 – 2%. After IVF and ICSI, it rises to about 25%.

Although the risk of multiple pregnancy after cleavage stage (2–3 day) embryo transfer with 2 embryos is lower than that after blastocyst transfer, according to recent statistics, it is still 24.2%. For more details, see IVF – the risks.

What are my options?

If you or your clinician considers that that you are at risk of multiple pregnancy, you should discuss transferring only 1 embryo (single embryo transfer, known as SET).

If one embryo is transferred during IVF (single embryo transfer), the risks of multiple birth are greatly reduced (although the risks are not completely eliminated as you are still 2 to 5 times more likely to become pregnant with identical twins after receiving fertility treatment than after natural conception ). 

Your clinic will discuss whether this is suitable for you. If it is, they should recommend transferring a single embryo and freezing any remaining ones for possible future use.
The latest research shows that, if you are young, healthy and have a good chance of conceiving with IVF, transferring only one embryo does not significantly reduce the chance of pregnancy.