Natural Killer (NK) Cells, Fertility, and Miscarriage: What You Need to Know

If you’ve been diagnosed with low AMH, high FSH, diminished ovarian reserve (DOR), premature ovarian insufficiency (POI), or recurrent pregnancy loss, you may be wondering if natural killer (NK) cells are part of the picture.

In this episode of Get Pregnant Naturally, we explain what NK cells are, when testing may be useful, and why many reproductive endocrinologists dismiss them. You’ll learn how looking at inflammation, gut health, nutrient deficiencies, and immune balance can make a difference for egg quality, implantation, and pregnancy outcomes.

We also explore what progressive fertility clinics are doing, what the research says, and how to decide if immunotherapy or intralipids are the right next step.

This podcast episode is for you if:

• You’ve had multiple implantation failures or miscarriages

• You’ve been told your test results are “normal” but feel something is missing

• You want evidence-based strategies to support fertility naturally and through IVF

What Are Natural Killer (NK) Cells?

NK cells are part of the innate immune system, designed to attack virus-infected or abnormal cells.

In the uterus, uterine NK cells help regulate implantation and early pregnancy.

• Balanced NK activity supports implantation

• Overactive NK cells may attack embryos, potentially leading to implantation failure or miscarriage

Why Looking Beyond Standard Testing Matters

While conventional medicine often debates NK testing, focusing on underlying factors can help:

Gut Health & Inflammation

Research links leaky gut, infections, and chronic inflammation to abnormal immune activation. Read more: Gut Health and Fertility

Nutrient Deficiencies

• Vitamin D – Low levels are linked to diminished ovarian reserve and poorer IVF outcomes. Read more.

• B Vitamins & Methylation – Low folate, B12, or MTHFR variants may impair implantation and egg quality

• Iron Deficiency – Low ferritin reduces oxygen delivery to the ovaries

Inflammatory Markers

Elevated hsCRP (C-reactive protein) is associated with recurrent pregnancy loss and poor IVF outcomes. Read more: hsCRP and Fertility

Addressing these underlying imbalances can help regulate NK activity naturally, instead of only relying on interventions like intralipids or IVIG.

What the Research Says About NK Cells and Fertility

• Elevated NK activity is linked to recurrent miscarriage, failed IVF cycles, endometriosis, and PCOS.

• Studies suggest immunotherapies like intralipids or IVIG may help some patients, but addressing underlying inflammation may be more effective long term

Not sure where to start? Download our most popular guide:  Ultimate Guide to Getting Pregnant This Year If You Have Low AMH/High FSH it breaks everything down step by step to help you understand your options and take action

For personalized support to improve pregnancy success, book a call here.

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TIMESTAMPS

[00:00:00] Low AMH, DOR, pregnancy loss - when to look at natural killer (NK) cells
[00:02:00] Who should consider NK cell testing (recurrent miscarriage, failed IVF, autoimmune, inflammation)
[00:04:00] Why most clinics dismiss NK testing + controversy in reproductive immunology
[00:05:00] Functional fertility view: gut health, nutrient deficiencies, inflammation, toxins
[00:06:00] Vitamin D, magnesium, and environmental exposures linked to NK cell activity

[00:07:00] Functional Fertility steps before NK testing: diet, gut health, sleep, stress
[00:08:00] Stress and nervous system dysregulation as hidden fertility disruptors
[00:09:00] Why elimination diet beats trendy diets for fertility and inflammation
[00:10:00] Functional testing: GI-MAP, minerals, B vitamins, and methylation markers

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TRANSCRIPT

[00:00:00] You're struggling with low A MH diminished ovarian reserve, unexplained pregnancy loss. You may have heard about natural killer cells, but what do they really mean for your fertility journey? Today we're diving into NK cells and when you should consider testing the conventional versus the functional medicine, functional nutrition approaches, and why Jumping into immunotherapy without preparing your body.

It could be missing the bigger picture. We'll also explore what progressive fertility clinics are doing, what the research says, and how you can take empowered evidence-based next steps say for you to listen. Let's go.

Welcome back. I'm Sarah Clark, founder of Fab Fertile. For over a decade, my team and I have helped hunters of couples improve their chances of pregnancy success, whether naturally or through IVF. We specialize in supporting those with low A MH, high FSH, diminished ovarian reserve, premature ovarian sufficiency, and recurrent pregnancy loss through functional testing and personalized fertility strategy.

Today we're digging into natural killer cells and why this matters if you have poor [00:01:00] egg quality implantation failure. And pregnancy loss. So this episode is for you as if you've had multiple implantation failures or miscarriages, and you're wondering what else could be going on. You've been told everything is normal, but your gut says there's more to investigate and you're considering IVF intra lipids or immunotherapy, but aren't sure if it's the right next step.

Thanks so much for listening. I'm so thankful that you're here. Make sure you hit subscriber follow, and if you know someone else who's on the fertility journey, please share this podcast with them. Should you test for natural killer cells and what to know before you start IVF or immunotherapy? Natural killer cells, they're part of the innate immune system.

They're designed to attack the virus infected or abnormal cells, and they're found in the uterus. Uterine natural killer cells play a role in implantation in early pregnancy and small amounts. They support implantation, but in overactive states, they may attack the embryo. So who should consider testing?

So if you had pregnancy loss, [00:02:00] recurrent pregnancy loss, more than two miscarriages. Implantation failure. Two. Failed embryo transfer with good quality embryos. A history of autoimmune disorders, thyroid, lupus, celiac, Hashimoto's, so thyroid, lupus, celiac, any autoimmune disorder going on. A history of inflammatory con conditions such as IB.

S. Which is a catchall term that doesn't really give us much clear path as to what's going on. But if you've got constipation, alternating between diarrhea, maybe you have IBSC, eczema, chronic fatigue, so inflammatory conditions, and women, if you've got diminished ovarian reserve, premature ovarian sufficiency, you're responding poorly to IVF despite age appropriate labs.

And these are some criteria that's used in some of the progressive fertility clinics, but they're often overlooked in conventional clinics. And many times they're just focusing if you've got pregnancy loss. We're gonna be talking more about the functional approach with natural killer cells. Sometimes we're doing all this testing and then the only recommendation is to do some [00:03:00] medication.

And so from a functional standpoint, we're not against medication, but in conjunction we need to see what's driving that. And if you've got a whole host of other things going on in your health, that could be driving the overactivity of the natural killer cells. Most reis are not gonna routinely test for NK cells.

Many say there's insufficient evidence. Some clinics are gonna dismiss uterine NK testing, citing variability and testing methodology, and unclear thresholds. And the controversy is that the NK cell activation, is it a cause or a byproduct of implantation failure? Many associations have not endorsed routine NK cell testing due to insufficient evidence, but that doesn't mean it's irrelevant.

Some progressive clinics are doing some endometrial biopsies, the immunotherapy, so intra lipids, Lovenox, and often those are combined with IVF cycles, but they're really not looking into lifestyle focus on what you can do to actually reduce the activation of these natural killer cells. Some of the research is telling us here [00:04:00] is there's some mixed data, but some studies are showing that elevated NK cell activity in women with recurrent miscarriage failed IVF cycles, endometriosis and PCOS.

A 2016 review found correlations, but emphasized individualized treatment is key. Reproductive immunology is emerging, but a lack of standardization in testing is gonna limit the broader acceptance. A functional approach should come first. So NK cell activation is often a symptom, but not the underlying cause.

So in the functional fertility approach, we're looking to see. If you got a leaky gut, maybe you've taken a bunch of antibiotics, you've got chronic stress for years, or even stress, you were on hormonal birth control, and then that can predispose you to a leaky gut. You end up being intolerant to all your favorite foods, and then it just lets in all these nasty bugs that then overgrow and then your body mounts an immune response, and you've got that intestinal permeability that's gonna drive systemic inflammation.

You've got nutrient [00:05:00] deficiencies, which we see this a lot, so especially with zinc. Magnesium. So 80% or more of us are deficient in magnesium. Our soil just doesn't really have the nutrients, and we suggest to anyone on the fertility journey to supplement with magnesium glycinate. We've been doing this for 10 years.

One couple both had high magnesium. We backed it up to look at their water filtration system. They were adding too many minerals to it. Most of us are deficient, and that could be why these, the natural killer cells are activating vitamin D. Literally, we see this all the time, people that have low vitamin D and there's also studies with low A MH.

So if your D is low, great, you wanna supplement? We wanna see why it's low. Is there gut infections that's driving it low? We like it 60 to 80. Just to cut off a zoom call with someone, they told me that they have low A MH. They had failed I UIs. They only tried for a short period of time, four months, but the vitamin D for the female partner was 18.

And yes, they're supplementing and also she's a hairdresser. And so I speak to many hairdressers actually, especially the ones that are applying color. So you're exposed to all those [00:06:00] heavy metals and toxins and the hair dye, and that could be then causing your body inflammation and then it just tilts things the wrong way.

Being able to then work on health before running off to I, UIs and IVFs, we can help do things to help get those heavy metals that are the body. You need to be very careful in that if you're doing chelation and heavy detox protocols, that's not recommended. You gotta do this in a very gentle. Approach and maybe you just have a high viral load.

So we see people that have Lyme or mold. Maybe you're in a moldy house or you've, there's been a leak. So you've got mold. Many people start going after the mold and the lime and all that stuff. So there is a way of basically where we're starting with doing an anti-inflammatory diet. Addressing the toxins, looking at the DNA of your stools, if you've got bacterial infections or fungal infections, and then also doing this from a personalized approach, looking at your gene variants and what are the specific diet and lifestyle and supplements.

Based on your genes, and then we can start going down to some of the other testing. There's a lot of people doing SIBO protocols and mold protocols [00:07:00] doing all this stuff, but you need to actually look at the low hanging fruit. If you've got all these inflammatory foods that's causing reactions to you, maybe you have a gut infection.

So we just need to be careful about following all these trends. We've gotta work on the basic. And the basics are eating the right diet, anti-inflammatory, the right sleep movement, and addressing stress. And then we add the testing piece in there, and then nervous system dysregulation. So you're just chronically stressed.

Being on the fertility journey is stressful in itself. And then the stress of life. And so that can then have all your biomarkers go outta balance. People tell me, I just want the testing. And the testing is part of our program. And that is critical because we can then get clarity and get some action and actually know what we need to address.

And then we need to have the mindset coaching along with it. 'cause that helps us reduce the chronic stress we've been under RE and then all the markers, we can see that our biomarkers can come back and balance as we do all this in conjunction. If you wanna do it slower. [00:08:00] Then you can say, I'm gonna hold on the stress piece and that I'm not stressed at all.

After doing this for years and years. I can tell you that is the elephant in the room. It is the stress that has tilted everything over the wrong way and then you end up getting food sensitivities. You end up having infections coming into your gut, but it's the stress that's brought it in. And that also being on the fertility journey, the pressure, the stress of that in itself.

So it's just a cumulative effect here. So we need to look at the whole body, and in this case, not just focusing on the natural killer cells and then not looking at all the rest of the things that are driving it and preparing the body before you go into an immune modulating therapy is crucial. You've gotta address that gut health.

Look at those food sensitivity. So I've definitely done a lot of episodes on gut health. Go check it out. I've done a lot of episodes on food sensitivity. Send me a message at hello@fabfertile.ca. Subject line 10 day, and then we will send you the elimination diet so you can get started with your partner right away.

Take out those top allergens. We need to calm the immune system, getting the right sleep, looking at your blood sugar so it's [00:09:00] stable, addressing your stress. And then that personalized anti-inflammatory diets. We don't wanna do carnivore or vegan or paleo or any of these keto, any of these trendy diets. It may have worked for someone, some fertility clinics touting the carnivore diet.

That's an anti-inflammatory diet. But then if you're going on that, it can just be too harsh. And you are just missing some of the crucial minerals that are needed for hormones. So that is not where we recommend starting do the elimination diet. That is the gold standard and we gotta remove some of those triggers, dairy and gluten and sugar and alcohol.

Then we wanna fast track it. We can look at some of the testing. So we do that GI Map test, and I've talked about this caution just doing one GI Map test and thinking we've done it all. No, the testing is part of our fab fertile method. But you need to be able to do the food in conjunction and the genetics, so then you can personalize it.

Otherwise, you'll just do a protocol. And I've seen people that do a GI math test and the protocol they have, they didn't even get a protocol. They, the protocol was take more probiotics. No, we do an extensive protocol after you get this test back. It's all [00:10:00] personalized depending on what we find. But our recommendation is not, here you go.

Here's some probiotics. We could do probiotics based on the strains that we're seeing, because a lot of times we see that your beneficial bacteria is very low. So that may be part of it, but that alone, that's not gonna shift the needle. We might wanna do some heritage tissue mineral analysis test to look at your nutrient levels.

Look at those heavy metals that can impact your immune function. May want, we may wanna identify if you've got a fungal issue going on. We can see that in the GI Map test. People do those a t candida diets. We need to be very careful that the candida or fungal is opportunistic. And if you go and attack it, it just goes into hiding.

There's a hierarchy of how we look at things. And those B vitamin deficiencies. We see people with the methylation issues. The homocysteine is outta balance and that could be why you're having a pregnancy loss. And I did a podcast episode on the high sensitivity C-reactive protein. We like to see that under one.

We see people had a success story there we're talking about where her C-reactive protein was slightly raised, 1.3, but she [00:11:00] had secondary fertility issues, low A MH. And once we got that into balance and the homocysteine, she needed more support with her methylation with her B vitamins. Lo and behold, you got pregnant within six months.

In this case, looking at the high sensitivity, C-reactive protein underlying inflammation, looking at your homocysteine, your methylation status. Looking at the A NA, so we did a podcast episode on that. The thyroid antibodies. You got thyroid antibodies. We like the TPO below 10, the TPG below 30, if it's elevated, that could be why you're having pregnancy loss.

That could be why you're having implantation failure. We've gotta look at all of this, not just in this case, focusing on the NK cells. And then we go off and do an immune therapy and we run off to IVF. We didn't address, we had a gut infection, food sensitivity, the chronic stress we've been under for years.

It's tilted all this the wrong way. So we need to be mindful as we deploy each of these pieces, and a lot of times no one's gonna say, Hey, wait, why is it there to begin with? So the intralipid therapy can be done if we've gone and done the functional side of things first. But if you've had the history of the autoimmune disease, the best thing to [00:12:00] do to reverse that is functional medicine, functional nutrition.

The inter lipids are not gonna work. People are like, let's do IV therapy, let's do the inter lipids. They may not work if you not corrected the terrain. So the diet, the stress, the toxins, the infections. Otherwise it's just a short term fix. So elevated natural killer cells, they matter, but they don't act in isolation.

So we wanna look at the other biomarkers and really see what's driving inflammation in your body. And once we address that, the whole body calms down. And then if we do decide to do the immune therapy, we can improve the chances of this working. 'cause there's a lot of clinics spending a lot of money.

Your money on this piece. And we haven't looked at what's happening from a foundational standpoint on your health. Remember, the majority of us can get pregnant naturally, and maybe you had pregnancy loss. Like this stuff is devastating. If you're going through this, I know it firsthand. I'm to diagnose A POI at 28.

So we need to be able to work on our health. We don't work on it now. It'll come back. It'll come back somehow in our postpartum period. The health of our children, [00:13:00] our health down the line. 'cause we pumped our body with so much medication. So we need to do this in a very targeted manner. We work with Type A people that gimme the plan.

Let's get to work. So we get the testing, here's the data, then we can help you execute. And if you're like, I don't feel stressed, I'm gonna tell you with a theme. We've worked with hundreds of people. The stress piece is a lot of the time what has tilted everything the wrong way. So we need to be able to work on that to reset your nervous system, and then the biomarkers can come back in place.

If you're ready to look at this completely differently, take control of your health and really be your own advocate here. Send me a message at hello@fabfertile.ca, subject line fertile, and I will send you a message and we'll get you on a call and we can talk about some options to help take care.

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How to Get Started With Functional Fertility Support

Book your call here to get your personalized plan and options to help improve pregnancy success either naturally or with IVF treatment. 

Check out our Fab Fertile functional fertility program here and learn how to improve AMH levels naturally.  We work with couples that have low AMH, high FSH, diminished ovarian reserve, premature ovarian insufficiency, and recurrent pregnancy loss.

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FAQs About NK Cells and Fertility

Q. Can NK cells cause infertility?

A. Overactive NK activity can interfere with implantation and early embryo development, leading to failed transfers or early pregnancy loss, but they don’t directly “cause” infertility.

Q. Can NK cells cause miscarriage?

Yes, research shows elevated uterine NK cells may attack the embryo and contribute to recurrent miscarriage. Often, NK activity reflects underlying inflammation, autoimmunity, or gut imbalance.

Q. Should I get tested for NK cells?

A. Testing may be considered if you’ve had:

• 2+ miscarriages

• 2+ failed embryo transfers with good-quality embryos

• A history of autoimmune disease (thyroid, lupus, celiac, Hashimoto’s)

• Chronic inflammatory conditions such as IBS, eczema, or chronic fatigue

Q. Can intralipids or IVIG help regulate NK cells?

A. Some fertility clinics use intralipids, steroids, or IVIG to suppress NK activity. These may help temporarily, but without addressing diet, gut health, nutrient deficiencies, toxins, and stress, results are often limited. Check out our episode here about reproductive immunology.

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RESOURCES

Stop Ignoring hsCRP and the Role of Inflammation in Diminished Ovarian Reserve

How To Prevent and Reverse Autoimmune Disease and Get Pregnant

Causes of Miscarriage Before 12 Weeks: What Most Doctors Miss

Improving Egg Quality and Fertility: The Gut Fertility Connection for Low AMH, High FSH, and Poor Egg Quality

How Reproductive Immunology Therapies Can Improve Pregnancy Outcomes with Dr. Marco Mouanness

Our favorite fertility tracker Inito (use code FABFERTILE15 to save 15) 

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