Hidden Cause of Infertility Affecting up to 50% of Unexplained Cases

Few words land harder than "unexplained." After months or years of trying, after the blood tests and the scans and the quiet waiting rooms, being told that nothing seems to be wrong can feel strangely heavier than a clear diagnosis. If everything looks normal, then why is conception not happening? The honest truth is that "unexplained" rarely means "unexplainable." More often, it means the right question has not yet been asked. One of those questions involves a quiet condition that many women never hear about, even though research suggests it may be present in a surprising share of unexplained infertility cases.

A common condition that hides in plain sight

Inside the uterus is a delicate lining called the endometrium. This is the tissue an embryo needs to settle into and grow. When this lining becomes quietly inflamed over a long stretch of time, the condition is known as chronic endometritis. Unlike a sudden infection that announces itself with fever and pain, the chronic form is often silent, or it causes only subtle signs such as irregular bleeding or mild pelvic discomfort. Because it does not have obvious symptoms that are easy to flag, it is therefore easy to overlook, and unortunately it frequently goes unrecognized.

How common is it? Depending on how it is measured, studies suggest this hidden inflammation may be present in anywhere from roughly one in five to more than half of women whose infertility has no obvious cause. It also appears often in women who have experienced repeated implantation failure or recurrent pregnancy loss. For a condition that can quietly stand between a woman and the family she hopes for, it receives remarkably little attention.

Why a calmer lining is so crucial

Conception is not only about a healthy egg and sperm meeting. The embryo also needs a welcoming place to implant. When the endometrium is inflamed, that environment changes. Ongoing inflammation can disturb the lining's receptivity, which is the precise biological readiness it needs at the exact moment of implantation. Over time, persistent inflammation can also lead to subtle changes in the tissue itself, including scarring and stiffening that further reduce the lining's ability to do its job. In other words, the issue may not be that conception is impossible, but that the "welcome mat" has unfortunately been quietly pulled away.

Why the usual approach may not always work

When inflammation of the lining is identified, conventional care generally focuses on addressing infection, since bacteria are involved in the great majority of cases. Yet this is also where many women hit an unexpected wall.

Research shows that the problem returns for a meaningful number of women, with infection coming back in roughly a quarter to a third of cases. Part of the reason lies in how these bacteria behave. Chronic cases often involve not a single organism but a mix of several at once, and these communities can build protective layers called biofilms that shield them and make them far harder to fully clear. Even more revealing, studies report that even after testing suggests the infection is gone, a significant percentage of women continue to face fertility difficulties. This points to something important. Clearing the bacteria does not automatically undo the inflammation, it may persist in some cases. The infection may be the original spark, but the lingering damage might become its own separate problem.

A wider way of thinking about the uterine environment

This is exactly where it helps to think beyond a single explanation. If targeting bacteria alone does not always restore a healthy lining, then the conversation needs to widen to include calming the inflammation itself and supporting the lining as it heals.

Science is beginning to move in this direction. A comprehensive 2026 review published in the journal Frontiers in Pharmacology gathered the growing body of laboratory and animal research into natural plant compounds that appear to influence these very processes, easing inflammation, reducing oxidative stress, supporting the protective barrier of the lining, and discouraging scarring. The researchers are careful and honest about the limits of this work. It is still early, it has not yet been confirmed in human trials, and it is not a replacement for medical care. What it does offer is a valuable shift in perspective, one that looks past simply removing a pathogen and toward restoring a healthy, receptive environment where pregnancy can take hold.

What this means for you

If you have been told your infertility is unexplained, the most empowering thing to know is that your process in assessment and treatment may not be finished. It can be worth gently asking your care team whether the health of your uterine lining has been fully explored, and whether a quiet, ongoing inflammation could be part of your picture. Sometimes the path forward begins not with a new treatment, but with a better question.

As a Naturopathic Doctor focused on reproductive care, my role is to look at the whole picture alongside your existing medical team, to help you understand the many factors that can influence fertility, and to support your overall reproductive wellness as you move toward your goals. You do not have to accept "unexplained" as the final word.

If you would like to explore your situation in a thorough and individualized way, I welcome you to reach out and book a consultation.

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Disclaimer: This blog is for informational purposes only and should not be taken as medical advice. Always consult with your Naturopathic Doctor before starting any new supplement, especially during fertility treatments like IVF.

About Dr. H. Singh, ND

Dr. H. Singh is a Fertility Naturopath based in Ottawa with over ten years of experience focusing exclusively on reproductive health.

He works with individuals and couples across Ontario and Quebec, supporting patients trying to conceive naturally or alongside treatments such as IUI and IVF.

Care focuses on evidence informed strategies to support egg quality, sperm health, hormonal balance, implantation, and early pregnancy.