Natural Killer Cells

Immune factors affecting pregnancy

Our immune system contains immune cells and defends us against germs and microorganisms. In most cases, our immune system does a great job of keeping us healthy but in some instances the immune system mistakenly recognises and attacks our own bodies, leading to inflammation, damage and disease.

People with autoimmune diseases such as Lupus and rheumatoid arthritis tend to have high levels of anti-nuclear antibodies that can lead to inflammation of the uterus and placenta, implantation failure and recurrent miscarriages.

Pregnancy is a unique situation in which the placenta ‘invades’ the lining of the womb and is a potential threat to the wellbeing of the mother. The mother’s immune system critical in establishing the relationship between the mother and the foetus, and must recognise that threat, but also respond in such a way that does not eliminate it.

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What are natural killer cells?

Natural Killer Cells (NK Cells) are the main immune cell-type found in the uterus. Their numbers increase through the menstrual cycle to peak at the time of implantation of an embryo. If an embryo does implant, NK Cell numbers increase further. Uterine NK Cell numbers start to decrease at 20 weeks of pregnancy and are absent at the end of pregnancy.

The prime role of NK Cells appears to be the early detection (surveillance) and elimination (killing) of cells that are not recognised as ‘self’. If the placenta and foetus are mistakenly recognised as a threat, NK Cell activity may potentially lead to problems during pregnancy, including miscarriages.

Current investigations into NK Cells are looking at the link between the success or failure of embryo implantation and miscarriage. However, it should be emphasised that the link between NK Cells and miscarriage is currently unproven. The current body of evidence is still very limited, and it is certainly possible that the studies so far simply describe an ‘association’ between NK Cell activity and reproductive failure – rather than a specific ‘cause and effect’.

How is natural killer cell activity tested?

Testing for NK Cell activity involves a simple blood test to measure the number and activation levels of the NK cells. The blood test can be performed at any stage of a woman’s monthly cycle as an alternative to, or in conjunction with, a traditional endometrial biopsy of the uterus.

An endometrial biopsy can be taken via a soft plastic catheter that is used to gently aspirate a tiny piece of the uterine lining, either while the patient is awake or under general anaesthetic, as part of a hysteroscopy. The biopsy is then sent off to the laboratory for testing. The biopsy has to be done at the luteal phase of the month (around Day 21 in a 28 Day cycle).

Who should be tested?

Your Fertility Specialist may recommend NK Cell activity testing if you have experienced:

  • recurrent miscarriage (defined as three successive miscarriages if aged less than 35 years, two successive miscarriages if aged over 35 years)
  • repeated IVF failure (defined as two or more unsuccessful fresh IVF cycles)

How do I book a natural killer cell activity blood test?

The NK cell activity blood test is available by appointment only at QFG clinics.

  1. Discuss whether this test is needed with your QFG Fertility Specialist
  2. Obtain a blood test request form from your QFG Fertility Specialist
  3. Contact your local QFG clinic to book your appointment time. This blood test can only be performed at certain times
  4. Attend your appointment and present your blood test request form to reception. One of our Phlebotomists will draw one small tube of blood collected into a specialised tube for the NK Cell blood test. Any additional tests on the request form may be collected at the same appointment
  5. Results of the test should be available within 4 business days after collection and will be sent to your referring QFG Fertility Specialist.

How is high natural killer cell activity treated?

There are a number of different treatments being prescribed for patients with a diagnosis of high NK Cell activity, including hormones and medications. Your QFG Fertility Specialist will carefully explain the most appropriate treatment for you based on your individual circumstances.

At this stage, treatments are at the trial stage only and further research is being conducted to determine the impact of immune system changes in women with high Natural Killer cell activity.

If you are interested in learning more about the NK Cell blood test, and the Queensland Fertility Group Fertility Specialists with expertise in this area, please call us on 1800 111 483 or complete the form below.

Learn about genetic testing