Causes & Treatment

What you need to know about blastocyst transfer

Jessie Day  |  30 Mar 2023


Blastocyst vs cleavage-stage embryo transfer. What’s the difference, and which one is right for you, and your IVF journey?

Whether you’re preparing for IVF or discussing different options with your doctor, fertility treatment involves a number of important decisions. The best clinics don’t just offer cutting-edge treatment – they’re also set up to help you make sense of the options, providing the right balance of information and support.

In this 101, we’re covering the ins and outs of blastocyst transfer, tapping into expert insight from the world-famous Assisted Conception Unit (ACU) at Guy’s and St Thomas’, London. With a global reputation as innovators in fertility treatment, coupled with the highest standard of care, this team are a UK go-to for stepping things up, TTC-wise.

Blastocyst vs embryo transfer is an important call, and still not standardised across the fertility landscape. Let’s hear the expert approach from Mr Tarek El-Toukhy, an expert consultant in reproductive medicine and surgery at Guy’s and St Thomas’. He is also the clinical lead of the Assisted Conception Unit at Guy’s Hospital and HFEA Person Responsible.

Over to Tarek El-Toukhy.

What is a blastocyst transfer?

In IVF terms, a blastocyst is a fertilised egg that’s been developed – or ‘cultured’ – in the embryology lab for five or six days after fertilisation. A blastocyst is given more time to reach an advanced stage and structure than, for example, a three day-old embryo. Practice shows that, because of this, a blastocyst has a better chance of implantation in the endometrium.

In the past, blastocyst transfer has been classed as an add-on – it still is, in fact, by the HFEA. But more and more often, we’re seeing better outcomes – potentially higher live birth rates and less risk of multiple pregnancy – with a blastocyst transfer, than transferring earlier at the two or three day embryo mark.

Fertilised eggs may develop into a three day-old embryo, but the majority of these won’t then make it to blastocyst stage. By working with blastocysts which have already achieved this stage of development, we have a higher chance of successful pregnancy.

Let’s step back a bit, and cover off blastocysts – they’re an essential part of the equation, after all! Thanks to our amazing embryology labs we can get pretty granular here, understanding exactly what’s happening in an embryo’s development, minute-by-minute.

What is a blastocyst?

By day three after fertilisation, a developing embryo should contain between six to ten cells. And by day five or six, the early-stage embryo is now classed as a blastocyst – a rapidly dividing cluster of cells.

A blastocyst is really a hollow ball of cells, which develop to form two layers. The inner layer is thicker, and becomes the more mature embryo, and the outer layer takes care of its protection and nourishment. By the time it implants in the endometrium, a blastocyst may contain hundreds of cells.

Guys and St Thomas-blastocyst transfer success rates

Day 5 blastocyst transfer success rates

With blastocysts, it’s a question of waiting, and whether this is worth it, given your individual profile and patient history. For the team at Guy’s and St Thomas’, we never work with a ‘blanket approach’, and will always tailor treatment to your unique situation.

However, because of its superior outcomes, we offer blastocyst culture time – and transfer – to all our patients who have two or more good quality early-stage embryos on day three after fertilisation.

Checking our most recent numbers in 2023, 70 per cent of our transfers are day five blastocyst transfers, and the success rate in the majority of those cases is over 50 per cent. Every clinic is different, but unlike many there’s no extra cost for the blastocyst transfer optionat Guy’s and St Thomas’.

What are the advantages?

The most talked-about advantages are, of course, better pregnancy outcomes. But there’s also a lower risk of multiple pregnancy, and freezing considerations to add to the mix. Here’s the run-down on why your team may recommend blastocyst transfer.

1. Higher success rates

By allowing the early-stage embryos to develop – ‘culture’ – until day five (some teams may wait until day six), we’re able to really see their structure and viability more clearly. This means we get a better chance of choosing the most superior embryo(s) for transfer, or freezing.

They’re also closer to the point where, in natural conception, they’d implant into the endometrium, which also impacts positively on success rates.

2. Less chance of multiple pregnancy

The longer an early-stage embryo is allowed to develop (within certain parameters), the more information we have about its viability. And this, in turn, means that we can help patients understand how many blastocysts may be best to transfer.

This is a key decision and question for so many of our patients, and going for blastocyst culture helps us make sense of the options, together.

Guys and St Thomas-is blastocyst transfer right for me

Is blastocyst transfer right for me?

This will depend on your individual profile, and discussions with your care team. But there are a few of the factors that we take into account, when building out a plan with our patients.

Age has a big impact on egg health, and if you’ve only produced a couple of good-quality embryos, many doctors recommend a day two or three transfer, instead of waiting for them to reach blastocyst stage.

What about the 2 blastocyst transfer success rate?

Clinical findings show that you stand as good a chance of having a successful pregnancy with a single blastocyst transfer, as transferring two. We tend to recommend going for the single blastocyst transfer, with the very best day five embryo available.

Our principle aim and ethos at Guy’s and St Thomas’ is to work with you on a plan that fits your unique situation. There’s no blanket approach – aside from maintaining excellence in our patient care – and we’re on-hand to talk through every option, whenever you need. You’ll be in the hands of the very best, whatever your decision, with a multidisciplinary team at the very top of their field.

From the blastocyst vs embryo decision to getting started and changing up your fertility treatment plan, the world-famous Assisted Conception Unit at Guy’s and St Thomas’ are ready to help. Connect today for an enquiry, consult, or GP referral

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