| Published: March 10, 2026 Last reviewed:March 10, 2026 Reviewed by: A/Prof Gavin Sacks - Group Medical Director and Fertility Specialist Genea |
When you're trying to conceive, understanding how your immune system affects pregnancy can feel overwhelming. At Genea, we're here to demystify complex topics like NK cells and explain how cutting-edge research is helping more women achieve successful pregnancies.
A/Prof Gavin Sacks, a pioneer in reproductive immunology at Genea, has been instrumental in introducing NK cell testing to Australia. His groundbreaking research has opened new pathways for women experiencing repeated IVF failure or recurrent miscarriage. Here are five essential things you need to know about NK cells and pregnancy.
1. NK cells serve two very different roles in your body
NK cells are a vital part of your immune system, but their function changes dramatically depending on where they are in your body.
In your general circulation, NK cells act as your body's defence force. One of the main functions of the immune system is to identify and remove 'foreign' cells from the body. A 'foreign' cell is any cell that doesn't match your genetics, including viruses, bacterial cells, and cancer cells. NK cells help your body recognise and defend against these infections and abnormal cells.
Inside your uterus, however, NK cells play a completely different role. Rather than attacking foreign cells, uterine NK cells work to establish a healthy environment to support a growing foetus. At the very beginning of a pregnancy, when the embryo implants in the wall of the uterus, NK cells are the most common type of immune cell present inside the uterus.
This dual role makes NK cells fascinating and complex. Understanding how they function in pregnancy has become crucial for helping women who struggle with implantation or early pregnancy loss.
2. Your embryo contains 'foreign' cells, but successful pregnancy depends on your immune system accepting them
Here's a biological paradox that makes pregnancy remarkable: an embryo is actually a source of 'foreign' cells. Half of the embryo's cells match the father's genetic material, not the mother's.
In any other circumstance, your immune system would identify these genetically different cells as foreign and work to remove them. However, a successful pregnancy requires your immune system to do something extraordinary, not reject the embryo even though it contains 'foreign' cells.
This delicate balance is where uterine NK cells play their supporting role. When functioning properly, they help create the right environment for implantation and early pregnancy development. They facilitate communication between your body and the developing embryo, supporting the formation of the placenta and ensuring adequate blood supply to the growing foetus.
Understanding this immune tolerance is essential when investigating why some pregnancies don't progress as expected.
3. NK cell problems could explain repeated IVF failure or recurrent miscarriage
While NK cells are essential for pregnancy, having too many activated NK cells or NK cells that are too active can indicate a problem with your immune system that may prevent implantation of the fertilised egg.
A/Prof Sacks' research has revealed significant findings in this area.
In fact, research has found that high numbers of activated NK cell levels are present in 15–25% of women experiencing repeated IVF failure or recurrent miscarriage.
This means that for roughly one in five women struggling with these challenges, an overactive immune response involving NK cells could be a contributing factor. If you've experienced:
- Multiple IVF cycles without successful implantation
- Recurrent miscarriages
- Unexplained implantation failure
NK cell testing could provide valuable insights into whether immune factors are affecting your fertility journey.
4. NK cell levels can now be checked through a simple blood test
Thanks to advances in reproductive immunology, checking your NK cell numbers and activity is straightforward. NK cell levels can be assessed through a simple blood test, making it an accessible diagnostic tool for women experiencing fertility challenges.
A/Prof Sacks has been instrumental in introducing NK cell testing to Australia, making this specialised assessment available to Australian patients at Genea. The test measures:
- NK cell numbers: How many NK cells are present in your circulation
- NK cell activity: How active or aggressive these cells are
Your fertility specialist can determine whether NK cell testing is appropriate for your situation based on your medical history and previous fertility treatment outcomes. This testing is particularly relevant if you've experienced multiple unsuccessful IVF cycles or recurrent pregnancy loss without an obvious explanation.
Understanding your NK cell profile provides important information that can guide treatment decisions and potentially improve your chances of a successful pregnancy.
5. The Bondi Protocol shows promising results for women with high NK cell activity
For women with high NK cell activity levels, A/Prof Sacks has developed a treatment approach that has shown remarkable success. A recent study conducted by A/Prof Sacks found that for women with high NK cell activity levels, live birth rates were over four times higher when the Bondi protocol was used (28%), compared with standard protocols.¹
The Bondi Protocol involves using prednisolone (a corticosteroid) and enoxaparin (also known as Clexane, a blood thinner) to help modulate the immune response during fertility treatment. This combination therapy helps to:
- Reduce NK cell activity to more appropriate levels
- Create a more receptive environment for embryo implantation
- Support early pregnancy development
These are significant improvements that translate into real families being created. The protocol takes its name from Bondi, reflecting A/Prof Sacks' Sydney-based research and clinical practice at Genea.
It's important to understand that this treatment approach is specifically designed for women who have been identified as having elevated NK cell activity through testing. The Bondi Protocol isn't appropriate for everyone, it's a targeted intervention for a specific immune issue.
Understanding your immune system's role in fertility
The relationship between your immune system and pregnancy is complex and nuanced. While we've learned that NK cells play a crucial supportive role in healthy pregnancy, we've also discovered that immune dysfunction can contribute to fertility challenges for some women.
If you've experienced repeated IVF failure or recurrent miscarriage, it's worth discussing NK cell testing with your fertility specialist. This simple investigation could provide answers and, more importantly, open up new treatment options that significantly improve your chances of success.
Your personalised fertility journey
At Genea, our commitment to reproductive immunology research and innovation means you have access to the latest diagnostic tools and treatment protocols. A/Prof Sacks' pioneering work in this field has helped hundreds of women understand and overcome immune-related fertility challenges.
Remember that every fertility journey is unique. Not everyone experiencing implantation failure or pregnancy loss will have elevated NK cell activity, and that's why comprehensive assessment is so important. Your fertility specialist will consider your complete medical history, previous treatment outcomes, and diagnostic results to create a personalised treatment plan.
What this means for your treatment
If NK cell testing reveals elevated activity levels, the Bondi Protocol may be incorporated into your fertility treatment plan. This targeted approach addresses the specific immune dysfunction that could be preventing successful implantation or early pregnancy development.
The four-fold improvement in live birth rates represents hope for women who have experienced the heartbreak of repeated treatment failure. It demonstrates how understanding the underlying causes of infertility can lead to more effective, personalised treatment approaches.
Moving forward with confidence
Advances in reproductive immunology have transformed our understanding of fertility and pregnancy. What once seemed mysterious; why some embryos implant successfully while others don't, is now increasingly explainable and treatable.
NK cell testing and targeted immune therapy represent just one example of how specialised knowledge and innovative treatment approaches can make the difference between continued disappointment and successful pregnancy. A/Prof Sacks' research continues to push the boundaries of what's possible in reproductive medicine, offering new hope to women facing complex fertility challenges.
If you're struggling with repeated IVF failure or recurrent miscarriage, don't assume it's just "bad luck" or that nothing can be done. Comprehensive investigation, including NK cell testing when appropriate, might reveal treatable factors that have been preventing your success.
Ready to explore whether NK cell testing is right for you?
If you're experiencing recurrent miscarriage or repeated IVF failure and suspect immune factors might be involved, A/Prof Sacks and our team are here to help.
Understanding the root cause of your fertility challenges is the first step toward finding the right solution. Rather than continuing with the same approach, let's explore whether immune factors are playing a role in your journey.
Contact our Fertility Concierge today to book an appointment with A/Prof Gavin Sacks. Together, we'll determine whether NK cell testing and immune therapy could be part of your personalised pathway to parenthood.
Disclaimer: Please note that this is a Genea Group blog and as such information may not be relevant for all clinics. We advise that you consult clinics directly for further information.
References
- Sacks G & Zhang J. Prednisolone and enoxaparin (clexane) therapy (‘the Bondi protocol’) for repeated IVF failure. Am J Reprod Immunol. 2022;88(5):e13616. doi: 10.1111/aji.13616.
FAQs
NK cells are a vital part of the immune system that help your body recognise and defend against infections and abnormal cells. In pregnancy, NK cells in the uterus play a different role, establishing a healthy environment to support a growing foetus rather than attacking foreign cells.
At the very beginning of a pregnancy, when the embryo implants in the wall of the uterus, NK cells are the most common type of immune cell present. If they are too active or their numbers are too high, this could prevent implantation of the fertilised egg or contribute to early pregnancy loss.
Research has found that high numbers of activated NK cell levels are present in 15–25% of women experiencing repeated IVF failure or recurrent miscarriage. This means roughly one in five women with these challenges may have elevated NK cell activity.
NK cell numbers and activity can be checked through a simple blood test. A/Prof Gavin Sacks has been instrumental in introducing this testing to Australia. Your fertility specialist can determine whether NK cell testing is appropriate based on your medical history and previous treatment outcomes.
The Bondi Protocol is a treatment approach developed by A/Prof Gavin Sacks that uses prednisolone (a corticosteroid) and enoxaparin (Clexane, a blood thinner) to help modulate the immune response during fertility treatment. This protocol specifically targets elevated NK cell activity to improve implantation and pregnancy success.
Research conducted by A/Prof Gavin Sacks found that for women with high NK cell activity levels, live birth rates were over four times higher when the Bondi Protocol was used (28%), compared with standard protocols.¹ This represents a significant improvement for women with immune-related fertility challenges.
No, NK cell testing is most relevant for women who have experienced repeated IVF failure or recurrent miscarriage without an obvious explanation. Your fertility specialist will assess whether testing is appropriate based on your individual circumstances and treatment history.
An embryo contains 'foreign' cells because half match the father's genetic material. A successful pregnancy requires the mother's immune system to accept these foreign cells rather than rejecting them. This immune tolerance is essential for pregnancy, and NK cells in the uterus help facilitate this acceptance when functioning properly.
Yes, when elevated NK cell activity is identified through testing, treatment approaches like the Bondi Protocol can help modulate the immune response. This targeted therapy has shown significant improvements in live birth rates for women with this specific immune issue.
Contact our Fertility Concierge to discuss your fertility history and whether NK cell testing might be appropriate for your situation. Our Group Medical Director and Fertility Specialist, A/Prof Gavin Sacks pioneered this testing in Australia, and can provide expert guidance on immune-related fertility factors.
Not necessarily. Some women with elevated NK cell activity do conceive naturally, but may experience recurrent miscarriages or implantation failure. Testing and treatment can help improve outcomes whether you're trying to conceive naturally or through fertility treatment.