natural killer cells and infertility

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Natural killer cells – the ‘unexplained infertility’

Natural killer cells – the ‘unexplained infertility’ By Dr Amanda Waaldyk, Angea Acupuncture & Yoga Have you been diagnosed with unexplained infertility by your GP, or ha...

Natural killer cells – the ‘unexplained infertility’

Natural killer cells – the ‘unexplained infertility’
By Dr Amanda Waaldyk, Angea Acupuncture & Yoga

Have you been diagnosed with unexplained infertility by your GP, or had two or more miscarriages? Do you have healthy embryos that fail to implant during your IVF cycle, or have you conceived naturally before, but are now struggling with fertility without any explanation?

In clinic, we are seeing an increasingly large number of women being diagnosed with high levels of natural killer (NK) cell activity. The topic of NK cells in relation to fertility is a controversial one amongst specialists, who hold varying opinions. Today, I am here to present to you an understanding of the role of NK cells and how they can affect your fertility.


If you took a snapshot of your current lifestyle, a typical day could look something like this:

> Wake up at 6am, check your phone and download emails.
> Go the gym for an hour, shower, get ready for work, make a smoothie and drink it in your car on the way to work.
> Arrive at work for an 8.30am start, eat lunch at your desk (often consisting of last night’s left-overs or a sandwich/sushi purchased from the cafeteria downstairs).
> Finish work at 6pm and drive home in peak-hour traffic.
> Muster up the effort to make dinner, sit on the couch, watch TV and check your phone.
> Go to bed. Repeat.

Sadly, the combination of the environment, accelerated lifestyle and pursuit to ‘have it all’ dictates the current state of our health. Gone are the days of living within the laws of nature. Our body is at war with itself and our immune system is suffering.


Our immune system is our natural defence system and has the massive job of protecting us against any bacteria, viruses and other harmful pathogenic invaders. When a foreign pathogen invades the body, its first response is to attack and protect the body against disease.

While our immune system has evolved over the years, today our bodies are under a lot of stress from the lifestyle we lead and the environment we live in, and it’s not coping. The combination of high stress levels and a toxic lifestyle is where we can slowly start to see immunological dysfunction in the body, and where NK cells may affect fertility.


Natural killer (NK) cells are a diverse group of cells that can be found in the blood and other areas of the body including the uterus. NK cells are one of several types of lymphocytes in the immune system protecting us from infections. If you read through online fertility forums, a lot of people will refer to NK cells by their marker, which is CD56. They earned the name ‘killer’ because it was found that these types of cells circulating in the blood were able to bind to and kill certain cancer cells and virus-infected cells. There are several types of NK cells and some have a negative impact on reproduction and some do not.

> Blood NK cells

Blood NK cells are quite different from uterine NK cells. They look different under a microscope, they react differently and they function differently.

> Uterine NK cells

NK cells are found in the uterine lining (endometrium) of all women, and are also the dominant maternal immune cells during the formation of your placenta. Their job is to protect the embryo and uterus against any infections and ensure it grows into a healthy baby.

After ovulation, uterine NK cell activity increases and is most active after you have ovulated and during implantation. NK cells become highly active during this phase, known as your luteal or secretory phase.

When a woman’s hormone production changes during her menstrual cycle, uterine NK cells will change. Levels remain low before ovulation and increase dramatically after, day by day.

> NK cells and fertility 

NK cells are present in every woman’s uterus and are the dominant maternal immune cells during the formation of the placenta of pregnant women. NK cells play an important role during the implantation and growth of an embryo.

Uterine NK cells are also an important mediator between the placenta and the uterus. They grow in large numbers to protect an embryo and ensure its development. They are there to attack anything that may try and harm the embryo, including viruses. If the NK cells detect that there is anything to attack in the pelvic cavity or uterus, your immune system sends an abundance of NK cells to the site to get to work. After ovulation and during early pregnancy, NK cells comprise more than 80 per cent of the white blood cell population seen in the uterine lining.


After ovulation and fertilisation of an egg, implantation begins. The specialised embryonic cells called trophoblast begin growing in the uterine lining – these cells later form your placenta. This transformation of cells is essential to ensure a normal blood supply to the foetus and placenta throughout pregnancy.

When your trophoblasts meet with the immune cells in the lining, they all become involved in cross-talk through a mutual exchange of substances called cytokines. There’s a lot going on in your body at this time and due to this complex immunological interplay, increased NK cell activity and autoimmune fertility can cause these cells can decide to attack the embryo instead of protect it.

Dr Alan Beer, a pioneer in the field of reproductive medicine, states that there are four types of immune problems in women with recurrent miscarriages, one of them being NK cells, which can lead to poor blood flow, interference with implantation, early miscarriage and lack of nutrition to the foetus, causing the body to mistakenly attack normal cells as if they were invaders.

In autoimmune infertility, the body begins to turn against itself. When an embryo tries to implant, our body recognises it as a foreign threat, sending NK cells to attack it, causing failed implantation, no implantation at all or a miscarriage.


What is frustrating for couples when actively trying, is that on paper everything looks normal. You are having sex at all the correct times in your cycle, hormone levels are normal, semen analysis parameters all point to his sperm being capable of fertilising an egg – yet nothing is happening. When this occurs your fertility specialist will normally diagnose you with ‘Unexplained Infertility’. There is always a reason why you are not falling pregnant, and in clinic it’s about finding out why you are not falling pregnant.

If you are having continual failed implantation, recurring miscarriages and no pregnancy, I recommend testing further to see if you have high levels of NK cell activity.

It is also entirely plausible that a ‘fertile’ woman may have future secondary reproductive failure. Women who conceived the first time and are having difficulty conceiving their second child who undergo further testing often have high levels of NK cell activity present. Currently, I am seeing a lot of this in clinic.


Natural killer cells can only be tested through a biopsy sample from the endometrium.

During menstruation we shed the NK cells with our endometrial lining and the biopsy is performed on day 21 of your menstrual cycle, when the NK cell count is at its highest.

The procedure is done at your fertility specialist and results take about two weeks to receive. If your NK cell activity reading is greater than 14 per cent on day 21 of your biopsy, then you are diagnosed with high levels of NK cell activity. Most women say the test is similar to having a pap smear.


With over 10 years of clinical experience and 90 per cent of my patients being diagnosed with high levels of NK cell activity, it is my opinion that this condition does exist. With our lifestyles being what they are today, my findings have indicated a need for us to take the time to evaluate our diary, relax and take time out when we can. We really need to practise and indulge in our ‘down time’. We need to bring our bodies back into a state of balance, out of this constant flight or fight and into REST and NEST, which is so important when it comes to our fertility.


If you’ve been diagnosed with elevated levels of NK cells, there is hope. There are two amazing doctors who specialise in this – Dr Nick Lolagtis is located in Melbourne and Dr Gavin Sacks is in Sydney.

You can find more information about them here:

> Dr Nick Lolagtis –
> Dr Gavin Sacks –

Have you had any experience of being diagnosed with elevated levels of NK cells, or overcoming your diagnosis? I would love to hear from you! #letsstarttheconversation


Amanda has just finished her latest digital book Body Baby Ready. Her new fertility guide takes a light-hearted, fun approach to a subject that can be challenging to navigate. This book is a fantastic resource for those trying to conceive, as well as those who want to learn everything about their fertility, body and cycles. You’ll have access to vital information and facts you haven’t yet discovered online, in discussion forums or even at your doctor’s office. Order your copy at


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