The Patient's Guide to Embryology

Does double embryo transfer double your chance?

Twin pregnancies should be avoided wherever possible, but there are circumstances where double embryo transfer should be recommended.

What is a double embryo transfer?

A double embryo transfer is when you create embryos in the lab through IVF and place two of them into the uterus instead of one.

Double, and even triple (or more!) embryo transfers were more common in the early days of IVF but now single embryo transfer is by far the most common approach. This is mainly because IVF has advanced significantly and embryos can now be frozen with survival rates close to 100%. Previously, any embryos that weren’t transferred were at risk of being lost during the freezing process but now embryos can be transferred one at a time and any extra embryos can be safely frozen for later use. Blastocyst transfer (day 5) is now also common in IVF, compared to the early days when cleavage stage (day 2 and 3) was more common. Blastocysts have a higher chance of implanting than day 2 and 3 embryos so double blastocyst transfer carries a high risk of twins.

The number of women having single embryo transfer has increased from 5.7% in 2000 to 64.2% in 2017.

Success rates – single vs double

It seems logical to think that more embryos in the uterus gives a better chance of one of them implanting. So why are so many people recommended to have only one embryo transferred?

The truth is that most women with more than one good quality embryo have a slightly higher chance of getting pregnant with double embryo transfer but the chance of having twins is much higher. As twin pregnancies carry many additional risks for the mother and the babies, it is important to avoid a multiple pregnancy wherever possible and in most cases the small increase in the chance of getting pregnant doesn’t outweigh the increased risk of twins. This means that if you have two good embryos, it is better to have those embryos transferred one at a time, and if both of those embryos are destined to be successful, it is better to have those babies one at a time.

What does current research say?

Ma et al. (2022). Comparisons of benefits and risks of single embryo transfer versus double embryo transfer: a systematic review and meta-analysis. Reproductive Biology and Endocrinology 20: 20

The data says:

There is no difference in live birth rate whether a woman has a single embryo transfer with a good quality embryo compared to double embryo transfer with one good quality and one poor quality embryo.

What does this mean?

There is no point in transferring a second poor quality embryo which isn’t suitable for freezing just to give it a chance, it can actually have a negative effect on the good quality embryo.

The data says:

Having a double embryo transfer with two poor quality embryos has the same chance of twins as single embryo transfer with a poor quality embryo.

What does this mean?

If all you have is poor quality embryos it may be better to have a double embryo transfer because it could increase your chance of getting pregnant but isn’t likely to increase your chance of twins.

The data says:

Single embryo transfer had a lower risk of caesarean section, excessive blood loss, preterm birth, low birth weight, neonatal intensive care admission and Apgar score <7.

What does this mean?

Single embryo transfer is the safest option for the mother and the baby.

Who should have a double embryo transfer?

It is important to avoid multiple pregnancies wherever possible, but there are circumstances where double embryo transfer might be recommended.

Women over 38 years old

As women get older, the likelihood of their embryos being abnormal increases substantially. Abnormal embryos are less likely to keep developing after being transferred, less likely to implant and less likely to make a healthy pregnancy. For these reasons, it is often recommended that older women have two embryos transferred to increase the chance of getting pregnant since the risk of having twins is lower than a younger woman having a double embryo transfer.

Women with recurrent implantation failure

Recurrent implantation failure is 3 or more embryo transfers which all result in a negative pregnancy test. Double embryo transfer may help to improve the chance of getting pregnant, particularly if other treatments such as ERA testing or embryo glue haven’t helped.

People with poor quality embryos

Current data shows that if you only have poor quality embryos, double embryo transfer can improve your chance of getting pregnant without significantly increasing the risk of twins. This is because poor quality embryos have a lower chance of implanting but may still be healthy.

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