31 October 2023

Why do many newly fertilised embryos fail to develop into blastocysts?

A new London Women’s Clinic study genetically testing almost 1000 embryos finds chromosome errors at a very early stage

Humans, unlike rabbits, are inefficient breeders. Even a healthy couple trying to conceive has no more than a one-in-four chance of success in a cycle of unprotected intercourse. And among the subfertile - as many as one in six of the population - these odds are much less, and in some cases may be zero. While assisted conception will help many to conceive, more than half of treatment cycle may be unsuccessful.

The main reason for this reproductive inefficiency, and for miscarriages too, is thought to be chromosome imbalances (‘aneuploidies’) within the embryo, which rise in prevalence with advancing maternal age. These can result in disorders such as Down syndrome or Turner’s Syndrome, but also explain why success rates in IVF and natural conception decline with advancing maternal age, especially after the age of 35 when the prevalence of aneuploidy increases dramatically.

Reproductive scientists have tested embryos for aneuploidy for over 20 years using a technique known as PGT-A (supported by the HFEA) – as it is now well understood that aneuploidy is the most commonly recognized cause of pregnancy loss in humans. So, the strategy for IVF labs testing embryos in IVF is to identify and select for transfer to the uterus, only those without aneuploidy. That way, the risk of pregnancy loss will be much reduced. To date, it has been assumed that most of these aneuploidies are already present in eggs before they are fertilised, but new research has shown otherwise.

A new study published in Genome Medicine by researchers from London Women’s Clinic and Johns Hopkins University in the USA – well summarised in News Medical – has found that the natural development of embryos may be arrested at the very beginning of its growth cycle, immediately after the egg has been fertilised by a sperm cell, and thereby terminate cell division and embryonic growth. And this arrest of embryo development would inevitably thwart any prospect of pregnancy, whether natural or assisted with IVF. The researchers, who included London Women’s Clinic alumni Michael Summers and Alan Handyside, found it ‘surprising’ that most of these embryo arrests were coming not from errors at the time of egg formation, but from errors happening in cell divisions soon after fertilisation.

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This is an important finding for IVF, where most embryos transferred to the uterus have been incubated for five or six days up to the blastocyst stage of their development. Studies show that results from blastocyst transfers are better than from transfers with younger embryos, but that only around one half of all embryos actually make it to the blastocyst stage. The other half experience embryo arrest at an early stage.

The latest London Women’s Clinic study, which may have important implications for the assessment of fertilised eggs in IVF, has now also found that the prevalence of aneuploidy among these arrested embryos is exceptionally high. Among almost 1000 embryos tested at an early stage, nearly half underwent developmental arrest because of genetic mishaps in their early development. This finding, say the researchers, may eventually help us find ways for more pregnancies to come to term in the fertility treatment process. So far, however, the study shows that aneuploidies, which frequently arise due to abnormalities in the first cell divisions after fertilisation, are the primary cause of arrest among IVF embryos.

What can be done to reduce the chances of miscarriage?

To combat the prevalence of aneuploidies where we can, at London Women’s Clinic we recommend PGT-A to our patients who are more likely to be impacted. The success rates we see for those who opt for IVF with PGT-A demonstrate the benefits of embryonic screening in the laboratory. ‘The appliance of PGT-A’, says Lead Embryologist in Genetics, Balsam Al Hashimi, ‘elevates overall success rates by selectively choosing the embryos with the best chances of implantation and survival.’

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Professor Nick Macklon, Clinical Director of London Women’s Clinic states, ‘we see this selective approach yields positive outcomes particularly in women over 40 who are most affected by the impact of age on egg and embryo quality. But we also see the value of this additional selective method for other services across our clinic, including Egg Freezing, IVF using Donor Eggs and Surrogacy.’ People often ask how to choose the ‘right’ or the ‘best’ embryo/ gamete and it is these selective methods taken by our embryology team that best support this decision-making process.

Want to know more?

You can learn more about the benefits PGT-A can have to your IVF journey on our website, and read about the new London Women's Clinic study published in Genome Medicine here.

All of our blog posts are written, edited, or produced by the London Women's Clinic Content Team. This is a collaboration between our expert writers, health editors, and the leading researchers and senior doctors at our Harley Street clinic.

‘We have two beautiful children - our family wouldn't exist without LWC Brentwood. Can't recommend them highly enough; IVF is an emotional rollercoaster regardless of your journey and we were supported at every step. Pricing is transparent and easy to understand, with payment plans available that made accessing any treatment and medication very flexible and affordable. The clinic became such a part of our lives for that short time, the care and support is so important and LWC Brentwood were brilliant. Maybe we will see them again for number 3!’

Victoria Hayman

10 November 2026, LWC Brentwood

‘I would like to express my heartfelt thanks to the entire team for supporting me throughout my IVF journey. I am delighted to share that I had a positive pregnancy test following my very first IVF cycle fresh embryo transfer, and I am now 9 weeks pregnant! The staff at the LWC Colchester satellite clinic are very supportive, approachable and always do their best to help you at every stage of the journey. I would definitely recommend LWC Colchester to anyone considering fertility treatment. A special thank you to Dr Timea Kovats, a highly experienced, knowledgeable and to the wonderful staff Jackie, Annette, Tracey. Their excellent guidance, expertise, care and supportive approach played a significant role in making my first IVF cycle successful. I am truly grateful for their dedication, encouragement and support throughout this journey. I am equally grateful to all the staff at Colchester satellite clinic and the London main clinic for their care and support throughout the entire process. Thank you once again for helping us achieve such a special milestone in our lives. We will always be grateful for your support! ❤️’

jigu

10 November 2026, LWC Colchester

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Mizzee West

10 November 2026, LWC Brighton

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10 November 2026, LWC Brighton

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Chiamaka Nelson

9 November 2026, LWC Cambridge

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Aruna Nelson

9 November 2026, LWC Cambridge

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Jessica Norman

9 November 2026, LWC Oxford

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Hannah Hale

9 November 2026, LWC Brighton

‘I honestly cannot recommend this fertility clinic highly enough. From the very beginning, the care, compassion and support we received were absolutely exceptional. Going through fertility treatment is an incredibly emotional journey, with so many ups and downs, but the team made us feel supported, listened to and genuinely cared for every step of the way. Nothing ever felt like too much trouble, and every member of staff we encountered was kind, understanding, professional and reassuring. What really stood out was how personal the experience felt. We never felt like just another number. The team took the time to answer our questions, put our minds at ease and guide us through what can sometimes feel like an overwhelming process. We are incredibly grateful for everything they have done for us and will never forget the part they have played in helping us grow our family. We now have our little miracles, and we couldn't be more thankful. If you're considering fertility treatment, I would wholeheartedly recommend LWC. Thank you from the bottom of our hearts for helping make our dream come true! ❤️’

Emma Hayman

8 November 2026, LWC Brentwood

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Kinga Arcana-Jones

7 November 2026, LWC Oxford

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Jess Palmer

5 November 2026, LWC Oxford

‘Very friendly staff and a lovely inclusive environment, had a wonderful experience here. Highly recommend for anyone looking at fertility preservation.’

T Ilagan

5 November 2026, LWC Oxford

‘As an LGBTQ couple we found LWC Colchester incredibly supportive, no question was too much. They were friendly and welcoming, with modern facilities, and made your journey feel very personalised. We would highly recommend them for your fertility journey.’

Jasmine Colman

5 November 2026, LWC Colchester

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James Purcell

5 November 2026, LWC Tunbridge Wells

‘Me and my husband can’t thank everyone at London Women’s Clinic enough for all the care and support throughout our recent treatment. Everything went really well, and we are so grateful to all the doctors and the entire team for looking after me. A special thank you to Mimi, Dr Barbara, Caroline, Trina and Elena from Embryology team and the Theatre Team - Rose, Martin and Amy F. Everyone was so kind, helpful and reassuring, and it really made a difference. Thank you all for everything. ♥️♥️♥️♥️♥️’

IsadelandCyril

4 November 2026, LWC Harley Street

‘I would like to express my heartfelt gratitude and appreciation to the entire team who supported us throughout our IVF treatment. ❤️ A special thank you to Ana-Maria,our nurse, for her kindness, patience, compassion and professionalism. She was always so caring, understanding and supportive, making us feel reassured and comfortable during such an emotional and challenging journey. We would also like to thank Dr Gill from the bottom of our hearts for his professionalism, dedication, expertise and the confidence he gave us throughout the entire process. IVF is not just a medical treatment; it is an emotional journey filled with hope, challenges and many feelings. Having such wonderful people by our side made everything so much easier. Thank you for your care, support and dedication. We truly appreciate everything you have done for us and would wholeheartedly recommend you to anyone beginning their IVF journey. Thank you for being part of our journey! ❤️’

Alexandru Predescu

3 November 2026, LWC Harrow

‘I would like to express my heartfelt gratitude and appreciation to the entire team who supported us throughout our IVF treatment. ❤️ A special thank you to Ana-Maria,our nurse, for her kindness, patience, compassion and professionalism. She was always so caring, understanding and supportive, making us feel reassured and comfortable during such an emotional and challenging journey. We would also like to thank Dr Gill from the bottom of our hearts for his professionalism, dedication, expertise and the confidence he gave us throughout the entire process. IVF is not just a medical treatment; it is an emotional journey filled with hope, challenges and many feelings. Having such wonderful people by our side made everything so much easier. Thank you for your care, support and dedication. We truly appreciate everything you have done for us and would wholeheartedly recommend you to anyone beginning their IVF journey. Thank you for being part of our journey! ❤️’

Mihaela-Clemansa Predescu

3 November 2026, LWC Harrow

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3 November 2026, LWC Colchester

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T Yang

3 November 2026, LWC Brentwood

‘We have used London Women's Clinic twice in the last two years for successful egg retrieval and two subsequent frozen embryo transfers. We have always been met with care, compassion and a personal approach. Every step from the initial consultation right through to the 7 week scan has been professional and polite, always accommodating our needs and timings. We can't thank the team enough for giving us such support towards creating our family.’

Lucy Richards

2 November 2026, LWC Tunbridge Wells

‘Myself and my husband owe it all to london womens clinic, they were amazing from start to finish. We previously were under another clinic and decided to make the change due to many reasons and we are so glad we did. They treat everyone as individuals, not everyones fertility journeys are the same. The small team at Colchester make it so personable not to mention how amazing all 4 women are that work here, their knowledge empathy and listening skills simply cannot be found at any other clinic. The list goes on as to why I would recommend LWC but everyone likes a to the point review. They genuinely care they dont treat you like a number and they help you through every hurdle that occurs. Our little boy wouldn't be possible without these 4, each of them play a bigger part than they realise. 💙’

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2 November 2026, LWC Colchester

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Yasmine Mora

30 October 2026, LWC London Bridge

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Louise

30 October 2026, LWC Oxford

‘Incredible service and professionals. They made me feel comfortable and safe the entire journey. Thank you!’

Luciana Lombardi

30 October 2026, LWC Cambridge

‘I had an absolutely amazing experience at LWC from start to finish! There are literally no wait times so we were able to get started pretty much straight away after consultation. The process was seamless, with a lot of flexibility if you need to change appt time. Nurses are amazing and so supportive. Special shout out to Kate and Chris who were so kind and made the whole experience so much better. Also the nurses on the ward were absolutely amazing but I can’t remember their names. I’m now discharged as I’m pregnant from my first try! However I will look forward to returning in the future for my second embryo which is currently frozen 😊’

Kathryn Jessica

27 October 2026, LWC Bromley