In this webinar, Dr Harry Karpouzis, Founder & Scientific Director at IVF Pelargos Fertility Group, breaks down one of the most misunderstood topics in reproductive medicine: immune factors in fertility. Many patients turn to immune testing after failed IVF cycles — but is it really the first step?
Dr Karpouzis explains why immune factors are often not the primary cause, and what should be carefully evaluated first — from embryo genetics to underlying medical conditions.
For patients worried that their immune system is blocking pregnancy, Dr Harry Karpouzis, Founder & Scientific Director, IVF Pelargos Fertility Group, says the most useful starting point is often not immunology at all, but ruling out the far more common causes of failed implantation and miscarriage first.
Immune-related fertility problems can sound compelling because implantation is, in part, an immune event. The embryo has to attach to the lining of the womb, and the body has to support that process rather than reject it. Inside the endometrium, immune cells help create the right environment for early pregnancy.
Among the most discussed are uterine natural killer cells. These are not the same as blood natural killer cells, and that distinction matters. A blood test may show one picture while the lining of the womb shows another, which is one reason immune testing in fertility remains controversial.
Uterine natural killer cells are not automatically harmful. They play a normal role in implantation, help small blood vessels form, and act through cytokines that support the embryo. The concern arises when these cells appear increased beyond what they should be, because that pattern may be associated with failed implantation or miscarriage.
That possibility has led many patients to seek immune testing early. But the evidence linking abnormal natural killer cells to recurrent implantation failure or recurrent miscarriage is described as weak and inconsistent. Major reproductive bodies such as ESHRE do not recommend routine natural killer cell testing or routine immune treatment.
For many patients, the most important message is also the least glamorous one: the most common cause of recurrent implantation failure and recurrent miscarriage is embryo abnormality. That is why moving straight to rare immune explanations can be expensive and misleading.
Before spending money on immune investigations, the embryo should be checked to see whether it is chromosomally normal with PGT-A. If that step has not been taken, immune testing may not be the best use of time or resources. A healthy embryo needs to be confirmed first, and only then does it make sense to keep searching if failure continues.
The same logic applies to abnormal embryos created in the lab. A 3PN embryo is considered an abnormal fertilisation, and the chance that it will correct itself and lead to a normal pregnancy was described as very, very, very slim. In practice, such embryos are usually not even frozen.
This is where immune testing is often misunderstood. Immunity can matter, but it is not a catch-all explanation for every failed transfer. Patients who have not yet evaluated embryo genetics or uterine factors may be looking in the wrong place.
A normal embryo still needs a receptive uterus. That is why structural and inflammatory causes should be investigated before immune treatment is considered. Hysteroscopy and laparoscopy can provide important information, including whether chronic endometritis or chronic infection is present.
This matters because inflammation or infection in the endometrium can increase natural killer cells and alter local immunity. In other words, an “immune” problem may actually be a sign of something more basic that can be treated directly. If infection or inflammation is driving the abnormal immune profile, treating the underlying cause may improve the immune environment, too.
Conditions such as endometriosis, PCOS, and endometritis also involve inflammation and can alter natural killer cells and cytokines in the endometrium. That makes them important pieces of the puzzle. Treating the underlying condition may do more for implantation than adding immunosuppressant medication.
This is also why steroids are not a simple answer. If there is a proven infection, steroids should be avoided because they can worsen it. In that setting, biopsy-based testing, along with methods such as NGS and PCR to identify infection, may point instead toward antibiotics. In some cases, hydroxychloroquine may be considered instead of steroids, but only after the underlying cause is identified.
When common causes have been ruled out, immunity can be assessed in two broad ways: blood tests and an endometrial biopsy. Blood testing is less intrusive and can provide a picture of general immunity. It may include markers related to Hashimoto, antiphospholipid syndrome, HLA antigens, ANA, and the balance between T-helper 1 and T-helper 2 activity.
But blood tests have limits. What shows up in the bloodstream does not always reflect what is happening inside the endometrium. That is why biopsy-based testing is often preferred when the goal is to understand the local immune environment where implantation actually happens.
The biopsy test mentioned for endometrial immunity is IMAP, with a similar test in France called Matris Lab. These tests are done at a specific point in the cycle, ideally around the stage that corresponds to embryo transfer. Timing matters because hormones such as estrogen and progesterone can affect local immunity inside the endometrium.
A biopsy may show an overactive, underactive, or mixed immune profile. That distinction is crucial. Immune-suppressing treatment should not be chosen blindly, because treating the wrong pattern may do more harm than good. The main drawbacks are practical ones: the test is intrusive, expensive, sensitive, and sometimes does not yield results.
There is also a time limit on how long results may remain useful. The immune profile can change within six months, so an older result may not reflect the current cycle.
Once embryo quality, uterine factors, infection, and other common causes have been addressed, immune treatment may be considered for selected patients. The approach is individualised and depends on whether the immune system appears overactive, underactive, or mixed.
If the immune system is overactive, the options mentioned include:
The goal is to reduce T-helper 1 dominance, lower natural killer cell cytotoxicity, and promote immune tolerance for implantation. In Greece, IVIG is not used, so intralipids are used instead.
Other medications may also come into play. Tacrolimus can be used when the immune system is overworking, although other medications are often preferred because they have a better side-effect profile. These are not casual add-ons. They are drugs with potential side effects, and they are intended to support implantation and pregnancy only when there is evidence that the immune system is actually contributing to the problem.
That caution extends into pregnancy. Steroids can be used, but doses should be reduced slowly. Hydroxychloroquine also has side effects and should be used at proper doses, with a reduction in pregnancy as appropriate.
Some recurrent losses are not primarily about natural killer cells at all. Antiphospholipid syndrome is a common cause of recurrent miscarriage and requires both clinical and laboratory diagnosis. The criteria mentioned included three miscarriages before 10 weeks, one miscarriage after 10 weeks, or a preterm birth, together with cardiolipin antibodies and anti-beta-2 glycoprotein.
This is one reason broad immune and clotting workups can be useful in selected cases. A patient may think she has an implantation problem when the real issue is a condition that affects clotting and placental development.
Lupus is often associated with antiphospholipid syndrome, but it is a separate condition and can exist without it. When lupus and antiphospholipid syndrome are present together, treatment may include Clexane, aspirin, steroids, and Plaquenil.
Clexane is used mainly for clotting disorders such as MTHFR, but it may also have an immunomodulatory effect. It may promote implantation, trophoblast invasion, vessel formation, and reduction of natural killer cell cytotoxicity. That overlap between clotting and immunity is part of what makes recurrent miscarriage workups so complex.
Some of the most specialised fertility immunology testing focuses on interactions between HLA-C antigens on placental cells and killer immunoglobulin-like receptors on uterine natural killer cells. Certain combinations are thought to be associated with miscarriage or implantation problems.
Even here, the evidence is not conclusive. These combinations are checked only when there is a relevant history. One pairing mentioned as a poor combination was HLA-C 2 together with AA, which may be related to recurrent implantation failure or recurrent miscarriage.
When that kind of incompatibility is suspected, options mentioned included G-CSF, single embryo transfer, intralipids, IVIG, progesterone adjustment, and steroids. But this is a niche area, not a routine first-line investigation.
Hormones themselves can influence the immune environment. Estrogen and progesterone can affect immunity inside the endometrium, which may matter in patients with a relevant immune history.
For that reason, one strategy is a freeze-all approach. Ovarian stimulation can proceed, embryos can be created, and transfer can happen later in a separate frozen cycle after the hormonal effects have settled. The frozen embryo transfer protocol can then be chosen according to the patient’s immunology status and endometrial findings.
That does not mean every patient needs frozen transfer for immune reasons. It means hormone-sensitive immune issues may be easier to manage when stimulation and transfer are separated.
Fertility immunology sits in a difficult middle ground: it may matter for some patients, but it is easy to overestimate and hard to test perfectly. The most practical path is usually the least dramatic one. Start with embryo quality, uterine anatomy, infection, inflammation, and well-known medical conditions such as thyroid disease and antiphospholipid syndrome.
If those have been addressed and implantation failure or miscarriage continues, immune testing may help refine the next step — especially when it focuses on the endometrium rather than assuming blood results tell the whole story. The goal is not to suppress the immune system just in case. It is to understand whether there is a real immune problem, what kind it is, and whether treating it is more likely to help than harm.
TSH should ideally be less than 2.5 when trying to conceive, preparing for embryo transfer, and during the first trimester. If anti-TPO antibodies are positive and there is Hashimoto’s, TSH is preferably kept below 2.5 because it can affect implantation. If thyroid hormones are markedly abnormal, thyroid disease can cause miscarriage and pregnancy problems and should be adjusted.
Before embryo transfer, it is sensible to perform a thyroid scan to rule out any other issues and to check thyroid hormone levels. If TSH is higher than 2.5, T4 replacement is used to lower it below 2.5 before proceeding. Because Hashimoto’s is an autoimmune condition, if it is associated with recurrent miscarriage or recurrent implantation failure, it is one more reason to investigate general immunity more thoroughly.
Immunity is not the main issue for everything. A common mistake is spending a lot of money on immune testing before checking more common causes, such as embryo genetics or uterine factors. Immunity matters, but it is not a panacea and should usually be assessed after more common causes have been explored.
This is also why some patients seek immune-focused help only after failed transfers elsewhere. Many clinics do not believe in immunity or do not follow this type of testing, but the right approach is still to assess the whole case from the beginning, starting with embryo quality and other common causes before moving to rarer immune factors.
Yes, tacrolimus can help. Other medications are often preferred because they have a better side-effect profile, but tacrolimus is an important medication and can be used in a similar way when the immune system is overworking, provided the doses are adjusted appropriately.
These drugs can have side effects. Steroids may have side effects, and although they can be used in pregnancy, doses should be reduced slowly. Hydroxychloroquine also has side effects and should be used at proper doses and reduced in pregnancy as appropriate.
These medications are intended to support implantation and pregnancy, but they should only be given when there is evidence that the immune system is overworking.
This cannot be answered from that information alone because the full history is needed. It may be chronic endometritis, and in that situation, antibiotics may be all that is needed. Prednisone should not automatically be assumed to be the right treatment without more information.
If there is a proven infection, steroids should be avoided because they can worsen the infection. A proper biopsy, such as ALICE, EMMA, or endometrium testing, can be used, along with NGS and PCR, to identify infection, and antibiotics may resolve the problem.
Hydroxychloroquine can be used instead of steroids in that setting, but the underlying cause must be identified first.
Estrogen and progesterone can affect immunity. When there is a relevant history, a freeze-all technique is preferred so stimulation can proceed, embryos can be created, and transfer can happen later after the hormones have cooled down.
The frozen embryo transfer protocol is then selected based on the immunological status and endometrial findings. Lifestyle measures such as antioxidant diets may help, but medication choices depend on whether the issue is increased natural killer cells, increased natural killer cytotoxicity, decreased mobilisation, or a T-helper 1 to T-helper 2 imbalance.
Ovidrel is a medication used for type 2 diabetes, and some small studies suggest it may reduce natural killer cell cytotoxicity and natural killer cells, but the evidence is not conclusive. It is not used much until more data are available.
3PN is an abnormal fertilization and the embryo is not normal. The chance of it correcting itself and leading to a normal pregnancy is very, very, very slim, and these embryos are usually not even frozen.
Breastfeeding is usually stopped before another embryo transfer, so ideally, these medications would not be needed during breastfeeding. If preparing for a new transfer while still breastfeeding, prednisolone can be used at specific doses, but it is not ideal for long-term treatment during breastfeeding.
Clexane and aspirin do not really affect breastfeeding, and intralipids do not have much data behind them. Gradual withdrawal from breastfeeding before transfer preparation is preferred, along with discussion with a paediatrician.
