Natural Killer Cells – A Cause Of Recurrent Miscarriage?

Natural Killer Cells - A Cause Of Recurrent Miscarriage?

Natural Killer Cells

Natural Killer cells (NK cells) have an important role to play in the early response to viral infections; they have also been linked with failure of pregnancy.

Natural Killer cell activity is now known to be a major cause of miscarriage and reduced implantation.

We also know Natural Killer cell activity can be mediated by high levels of stress, as well as by auto-immune disease.

Recent reports in the media and on the Internet have exposed women to a baffling amount of conflicting information about tests for NK cells and ‘cures’ for infertility and miscarriage.

Increasingly, clinics are offering tests to measure the number and activity of circulating NK cells.

As a result of these investigations, many women are then offered treatments such as steroids, intravenous immunoglobulins, and tumour necrosis factor blocking agents.

Natural Killer cells (identified by the surface marker CD56) are the dominant type of maternal immune cells that populate the uterine mucosa (the inner wall of the uterus) during formation of the placenta.

These uterine NK cells are also present in the endometrium (uterine lining) of non-pregnant women, when under the control of ovarian hormones.

After ovulation, uterine NK cells increase vigorously, so by the late secretory phase, they account for at least 30% of the endometrial stroma (connective tissue).

Uterine NK cells accumulate in large numbers at the implantation site. Here they are in close contact with the invading placental trophoblast cells, which transform the spiral arteries into high conductance vessels.

This transformation is essential to ensure a normal blood supply to the fetus and placenta throughout pregnancy.

Two Types of NK Cells

Here’s something important to note: there’s a huge difference between uterine NK cells and the NK cells that circulate in the bloodstream, and can cause miscarriage.

The best way to explain the difference between uterine NK cells and the NK cells circulating in the peripheral bloodstream is to explain what they do in the body.

Basically, uterine NK cells grow in large numbers to protect the embryo and ensure its development. They are there to attack anything that might try to harm the embryo, such as viruses.

Other NK cells are designed to circulate in the body, via the bloodstream, and are very important in protecting us from viruses and cancer cells.

What Causes The Problem?

Here’s the problem: if any inflammation is present in the pelvic cavity or the endometrial lining (endometriosis, PCOS, tubal inflammation etc.), the immune system responds by sending the other NK cells in the blood stream to attack and kill off inflammation.

When the NK cells in the blood stream (not the uterine NK cells) reach the site of inflammation in the uterus or pelvic cavity, the uterine killer cells that are protecting the embryo move out of the way to let the incoming NK cells do their work.

Sometimes, unfortunately, these cells see the embryo as a foreign organism, so it is attacked and killed.

This is how the problem of recurrent miscarriage arises.

That’s why it is so important that any inflammation in the uterus or pelvic cavity is addressed, so as to solve the problem.

It’s also one of the reasons why any woman experiencing fertility problems should have a laparoscopy, prior to any further fertility treatment. A laparoscopy is the gold standard for addressing and treating any problems in the uterine and pelvic cavity.

In order to get a diagnosis of high levels of NK cell activity in the uterus, a biopsy needs to be done between day 24 and day 28 of a menstrual cycle. This is because NK cells are at their highest levels during this phase of the menstrual cycle.

The procedure can be done in a doctor’s room and does not require anaesthetic. Unfortunately, it is invasive and inconvenient, but not painful. Most women say the test feels similar to having a pap smear. It cannot be done during an IVF cycle.

Once the biopsy is done, the small amount of endometrial tissue is sent away for genetic testing. Most of the testing in Australia is done in Sydney, as there is really only one lab that does proper processing. The results are usually available after about two weeks.

In Sydney, most of the testing and screening is done through several specialists at IVF Australia, and in Brisbane, only one specialist screens and treats for NK cells.

Specialists in Australia often fail to do this test. This is astounding, given that it’s a very simple procedure that can produce great results and treatment, and provide answers for those who have been enduring the heartache of miscarriage with no explanation.

NK Cells And The Immune System

As mentioned earlier, these naturally occurring cells are immune mediated: they can occur due to an overactive immune system, and inflammation in the body.

This is why immune disorders such as thyroid problems need to be screened for as well.

When investigating thyroid problems, it is important not to screen just for TSH (Thyroid Stimulating Hormone) levels, but also for T3 and T4 levels.

It’s even more important to screen for thyroid antibodies. Many women with the beginnings of thyroid disease have normal TSH levels but can have very high antibody levels.

Treatment for Natural Killer Cells

There is really only one treatment in western medicine for NK cells. It involves the use of steroids, pre and post conception. The main steroid used is prednisone, given in a dosage anywhere from 10mg to 20mg daily.

Steroids, however, have major side effects for the mother and her unborn child.

The way in which steroids dampen down killer cell activity is to suppress the whole immune system. This leaves the mother more prone to infections, colds and flu, and other immune disorders.

The ideal would be to regulate the number of killer cells, rather than use the blanket suppression approach. But to date, this is all western medicine has.

Australia is a leader in NK research, with regard to fertility, and most of the work is being done by Dr Gavin Sacks at IVF Australia.

The good news is that we have access to some fantastic natural products that can help to reduce inflammation and regulate NK cells.

At my clinic, we have seen great results in patients who use these natural anti-inflammatory products. They take them while they are trying to conceive and during pregnancy; there have absolutely no side effects and cause no harm to the pregnancy.

We also have an effective herbal formula we recommend to everyone. It can be taken for colds or flu, for immune support, and as a preventative. It dampens down inflammation and helps to regulate NK cell activity.

We’ve started to recommend this treatment to clients who come to us with fertility concerns, in case they have undiagnosed Natural Killer cells present.

There are also Chinese herbs that can regulate Natural Killer cells. You will need a consultation, however, before they can be prescribed. The major functions of a prescribed herbal formula are to prevent miscarriage, to increase circulation into the uterine lining to assist implantation, and to help reduce inflammation – the problems caused by NK cells.

Natural Killer cells can be a factor in unexplained infertility, and might be more prevalent in those with autoimmune disease or other inflammatory conditions such as endometriosis, tubal disease and PCOS (polycystic ovarian syndrome).

In my clinic, I screen my fertility patients for NK cells, especially those who have had recurrent miscarriage. I believe this initial investigation can save couples the heartache of going through a miscarriage, especially if Natural Killer cells might be the cause.

Recommended reading: See our article on the MTHFR gene mutation which is also linked to recurrent pregnancy loss.

Articles posted on BellyBelly which are not written by Doctor Andrew Orr are the opinions of BellyBelly and not necessarily the opinion of Doctor Andrew Orr.

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Doctor Andrew Orr is a Women's Health and Reproductive Specialist, with Masters degrees in both fields. His other qualifications include a BSc and BHSc, and he is a qualified nutritionist and doctor of Traditional Chinese Medicine. Doctor Orr's fertility work with couples has resulted in the births of over 12,500 babies.


  1. Hello, I’ve just had my 3rd MC in my 6th cycle of Ivf. I have unexplained fertility and was never offered NK cells testing. If I had been offered I maybe would not of had so much heartbreak. I’m not due to
    Go back to my clinic now as I don’t have any embryos left, but I need to know how I can get my NK cells tested now. Thank you

  2. I had different cases of pregnancy loss..preterm labor,missed abortion and last ectopic which had me my salpingectomy operation..i dont know what’s the main reason behind it but they offered me APAS fanel and anti beta.thanks for knowing the NK cells..

  3. Hi is there a natural anti inflammatory product that would regulate nk cells that you recommend? Ive recently been diagnosed with high nk cell cpunt after two miscarriages ans 6 months of failing to conceive. Conceptshen isn’t available where I live. Also, the herbal supplement you recommend – what is that?

  4. Hello – I live in the UK and have a friend who has experienced difficulty conceiving and on the two (known) occasions that she has, she has miscarried before 12 weeks. As the fertility doctors/consultants she has seen have been rather abrupt and unhelpful, she’s unwilling to make any further appointments at this stage. Are there any herbal immunosuppressants I can recommend to her (in UK)? Any help would be much appreciated. Thankyou.

      1. Wow, that’s really interesting too. I’ve just completed a human biology A level so a lot of that makes sense. I just wish I could refer her to you personally! You’re not in the UK are you?!

        1. Dr Orr is in Australia. He does Skype consultations, but he would need to treat in person. Holiday to Australia? Weak Australian dollar at the moment, should be cheap as chips, hehe!

  5. Hallo Doctor,

    My sister was diagnosed with NK cell toxicity.She was treated with Intralipid Infusions.Two IVF attempts failed and then she was diagnosed with increased NK cell toxicity and treated with Intralipid before her third IVF cycle.But even the third was a failure.

    I read your post about natural remedies for NK cell toxicity.I would like to know more about it and also if the product is available in India.

    Is there any other natural method to treat the NK cell toxicity,like food supplements etc,

    Kindly consider our case and give your valuable advice.

    Yours truly,
    Dhanalakshmi Kesavaram

  6. Hello dr Orr,
    I am 28 and have been trying for a baby with my husband 33 since over a year. All attempt to get pregnant has ended up in miscarriages, I have had four miscarriages now in total, all were 5,6 7 and 5 weeks, the last one was in October 2015
    I have been to the hospital several times and the doctors and my gyneocologist has said all test done so far came normal. And he has adviced us to contact a private Nk cell clinic here in UK, emotionally I am drained, it’s affecting my everyday life, work and happiness. All my friends around me are either pregnant or giving birth
    I’ve been asked by gyneocologist to start taking progesterone supplement immediately I realised I’m pregnant again. Please someone help me!! I just need my little angel to stay with me

    1. Doctor Jans Bronsen at Warwick Hospital pioneered the NK test. Or Shioban Quinby, who also works there and has written articles on it.

      My wife had similar losses at 6 weeks, and thought it might be due to NK cells. She had also been on the pill for over 10 years.

      Jans recognised symptoms and didn’t think it would be NK, but the symptoms were very common for woman who miscarried at six weeks. He recommended the test anyway because the biopsy produces stem cells and a groove in the Uterus, which helps with implantion.

      The procedure was super traumatic for my wife (because it’s so invasive and like having an intense period immediately, without any warning) but we were given progesterone and instructed to try for a baby immediately.

      Ultimately, the test came back negative, but thanks to Jans and Shioban, we are now entering our third trimester and baby is active and growing at a normal rate.

      We think our problem might have been because she had been on the pill for so many years. The pill can contain progesterone in it to trick the body into thinking it is already pregnant, and her body might have forgotten how to produce it naturally, resulting in recurrent miscarriages at six weeks.

      I hope this helps

    2. Hi Winnie I am going through the same thing right now, I have had 2 miscarriages and all my reports have come normal! My nk cell tested really low and my immunologist suggests this may be the reason why. Plz email me and let me know what you did will be really helpful! They have put me on hcqs and suggest I wait for six months until i try to conceive again, this wait haunts me and not sure if everytging will be fine the next time. Thanks

  7. Hello , I have just recently been tested for natural killer cells after my husband and I been trying to have a baby for about 5 years. The doctor told me my levels were elevated and that I should take intralipid with our next in-vitro. My husband and I both have done the research on the side effects and I feel I need to do a more natural way to lower my natural killer cells. I read about the conceptshen . Can you please send me more info on this ? Do you know what I can do here in Canada to lower this and to try and stay away from strong meds with dangerous side effects. right now I see acupuncturist and a Sho Ti practitioner (herbalist) .

  8. My sister in law has a son aged 11 and hasn´t been able to conceive again. She has given up on conceiving naturally and has had 5 or 6 failed IVF attempts. Her HCG levels increase with the first test but decrease shortly after and then there is nothing. I would so love to tell her about the hope of a NK testing or treatment if she hasn´t done that yet. I know she is tired of taking many hormones for IVF treatment, but if the NK testing is what is causing her not to conceive I think she would try taking whatever meds she needs to. The idea of natural remedies is of course wonderful and something I´m sure she would want to try.

    I would really appreciate your valuable advice,
    Yours truly,

    1. Question: may I ask your qualifications? Reason I ask is I believe the general public are unable to access peer reviewed journals on this topic. Are you the obstetrician Peter Wein? If so, I have supported one of your clients 🙂

      Dr Orr’s professor is Gavin Sacks, who has done all the research here in Australia on NK cells through IVF Australia. He’s pretty knowledgable and presents seminars on the latest information about NK cells.

      Thanks 🙂

  9. Hi all, hoping this helps all of those from uk. I live in Yorkshire and after suffering 3 miscarriages all around 6- 7 weeks in the past 2 years and the last loss was twins 🙁 we were recommended by our Leeds hospital consultant to contact Dr Sioghan quenby @ Warwick who is recognised in this nk cell field within the nhs although it’s a private charge to all patients it’s worth the £360 and she and dr broken are doing great research. I had the biopsy and yup my levels were 15% and out of control. They should be >5% and ideally 1-3! Due to age and that we don’t have time on our side ( I’m now 42) I’ve now completed my first Icsi IVF cycle and I’m on high dose steroid tablets, plus the regular post IVF meds- prednislone intramuscular injections and clexane. I’ll post an update of any success and best of luck to all who are reading the post and are too suffering or suffered loss. Keep positive xxx

  10. Hi,

    I have had 3 MC (all at 9th week), diagnosed with ANA+ speckled pattern, was on Dexamethasone 10 mg, wysolone 7.5mg, HCQS 200mg, baby asprin 150mg…during pregnancy but still i miscarried.

    Anyone faced same n got successful pregnancy..

  11. Hi there. I am currently experiencing my 14th miscarriage with no live births. With this last pregnancy I have been on 20 mg prednisone since ovulation still resulting in miscarriage. I have underwent extensive testing that has all come back normal. The only thing I haven’t been tested for is elevated NK cells, but prednisone should have helped with this. Any suggestions? I just turned 38 and have lost all hope.

    1. If you’re NK cells are elavated you should also get treated with intralipids. That’s what i am doing. Many RI believe this is a great treatment.

    2. Hi Kelly
      I took prednisone to lower NK cells but it did not work. It had awful side effects, I gained 20ks, lost a lot of hair…
      Eventually I could not go on anymore after my 5th miscarriage I decided to see a Chinese Dr who put me on a detox, then a treatment and after 8 months of herbs & acupuncture my biopsy came back normal & we have a beautiful baby girl.
      Get the biopsy!

  12. Hello. I have been diagnosed with overactive killer cells.. Iam interested in receiving more information please..I live in the USA. An I was wondering if I could buy the stuff for treatment over the web ..thanks lucinda. Please respond to my email.

  13. Hi,

    When do the miscarriages due to NK cells usually happen? Are they mostly first trimester miscarriages?


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