What does blastocyst development tell us about IVF success?
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Key takeaways
- Not every fertilised egg develops into a blastocyst, the stage an embryo reaches after five to six days of growth in the laboratory.
- A new review by Genea's Chief Scientific Officer, Associate Professor Dean Morbeck, and Diamond, examined whether blastocyst development rate is a reliable way to predict how a new IVF technique or device will affect pregnancy rates.
- The review found that when a laboratory change leads to fewer blastocysts forming, this consistently predicts lower pregnancy rates. When blastocyst numbers are maintained, pregnancy rates hold steady.
- This means blastocyst development can act as an early, reliable signal, allowing new IVF technologies to be assessed more quickly and safely.
- Faster, safer assessment of new techniques helps accelerate genuine improvements in IVF laboratory care.
What is a blastocyst, and why does it matter?
After an egg is fertilised during IVF (in vitro fertilisation), it does not become a blastocyst straight away. Over five to six days of growth in the laboratory, a fertilised egg divides and develops through several stages, and only some embryos reach the blastocyst stage, a more advanced structure with a fluid filled cavity and two distinct groups of cells that go on to form the placenta and the baby.
Not every fertilised egg makes it this far, and the proportion that does, known as the blastocyst development rate, is closely watched by embryology teams. It has long been used as one marker of how well a laboratory's conditions and techniques are supporting healthy embryo growth.
But how reliable is this marker, really, when it comes to predicting whether patients will go on to achieve a pregnancy? That is the question this new review set out to explore.
The question this review set out to answer
A 2025 review by Morbeck and Diamond, published in F&S Reviews, examined the evidence behind using blastocyst development as an indicator of whether a new IVF technique or laboratory device is likely to achieve good pregnancy rates.
This question matters because fertility laboratories are constantly evaluating new technologies, from culture systems to incubators to laboratory devices, and need reliable, timely ways to understand whether a change will help or hinder patient outcomes. Waiting for full pregnancy and live birth data on every new technique can take a long time. If blastocyst development rate is a trustworthy early signal, it could allow safer, faster evaluation of new approaches before they are adopted more broadly.
Why blastocyst rate is used as a marker
Because blastocyst development happens relatively early, within the first week after fertilisation, embryology teams have long used the proportion of embryos reaching this stage as an early indicator of how well laboratory conditions are supporting embryo growth, well before a pregnancy outcome is known.
This is what made blastocyst development rate a useful subject for this review. If it genuinely predicts pregnancy outcomes, it offers laboratories a much faster way to check whether a change is helping or harming patient results.
What the review found
Morbeck and Diamond's review identified a consistent relationship between blastocyst development rate and pregnancy outcomes. When a change to laboratory practice, whether a new culture system, device, or technique, resulted in fewer embryos reaching the blastocyst stage, this reliably predicted a corresponding drop in pregnancy rates. Conversely, when blastocyst numbers remained steady after a change, pregnancy rates also remained steady.
This consistency is what makes the finding valuable. It means blastocyst development rate is not just a laboratory curiosity, it functions as a genuine, evidence backed early warning signal. A change that quietly reduces blastocyst numbers is very likely to also reduce a patient's chance of pregnancy, even before enough pregnancy data exists to confirm it directly.
What this means for how new IVF technologies are assessed
Fertility laboratories are constantly working to refine their techniques and adopt new technology, from incubation systems to culture media formulations to laboratory devices. Historically, fully evaluating whether a new approach is safe and effective could mean waiting for enough patients to complete treatment and achieve, or not achieve, a pregnancy, a process that can take a long time and expose more patients to an unproven change in the meantime.
This review supports a faster, safer alternative. By monitoring blastocyst development rate closely when introducing a new technique, laboratories can identify early warning signs within days rather than months. If blastocyst numbers drop, that is a clear signal to pause and investigate before the change is used more widely. If blastocyst numbers hold steady, laboratories can proceed with greater confidence.
At Genea, this kind of evidence based approach to laboratory innovation reflects how we operate. Our Chief Scientific Officer and research teams continually assess new techniques and technology against the best available evidence, so that changes made in our laboratories are always grounded in what genuinely improves outcomes for patients.
What this means for you
If you are undergoing IVF, you do not need to track blastocyst development rates yourself, your embryology team monitors this closely as part of routine laboratory quality control. What this research means for you is broader reassurance, it shows that when fertility laboratories introduce new technology or techniques, there are reliable, evidence based ways to check that the change is genuinely benefiting patients, and to catch problems quickly if it is not.
This kind of research also reflects the value of choosing a fertility provider with genuine scientific leadership. Understanding not just what works, but how to reliably test whether something new is actually working, is part of how world leading fertility care continues to improve safely.
If you would like to understand more about how your own embryos are assessed and monitored during treatment, our team of Change Makers is always happy to explain the process in plain language.
FAQs
About the authors
Dr. Dean Morbeck
Genea Chief Scientific Officer
Dr. Dean Morbeck, PhD, HCLD, is Chief Scientific Officer for Genea Fertility and adjunct Associate Professor at Monash University.
View profileReferences
- Morbeck, D. E., & Diamond, M. P. (2025). Blastocyst development in assisted reproductive technologies: A narrative review evaluating its role as a surrogate marker for pregnancy outcomes and live birth success. F&S Reviews, 6(2), 100094. https://doi.org/10.1016/j.xfnr.2025.100094
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