Chronic endometritis: a cause of failed implantation

What exactly is chronic endometritis?

Chronic endometritis is a mild, ongoing inflammation of the endometrium (the tissue lining your uterus), usually caused by bacteria. What sets it apart from other uterine issues is how long it lasts. Doctors call it chronic once it lasts 30 days or longer. It's a separate condition from any inflammation related to pregnancy itself.

In other words, this isn't a short infection that flares up and clears in a few days. It's a slow, ongoing process happening in tissue that needs to be ready for an embryo to implant. That's exactly why it matters in fertility care, even though it can look like a minor issue on paper.

Why is this condition so easy to miss?

One defining feature of chronic endometritis is how quiet it usually is. It's often symptom-free entirely. When symptoms do show up, they tend to be vague rather than distinctive. The most common ones are abnormal uterine bleeding, pelvic discomfort, and unusual vaginal discharge.

Each of those symptoms, on its own, could point to a dozen different things, such as a hormone shift, or something else entirely. That overlap is exactly why chronic endometritis so often goes unrecognized. It's usually found only when someone is specifically investigating implantation trouble and starts looking past the more commonly tested causes.

How is it actually diagnosed?

Chronic endometritis rarely causes clear symptoms. It also doesn't show up reliably on standard blood or culture tests. So doctors can't rule it in or out with routine bloodwork or a typical swab. Confirming it takes a more direct look at the tissue itself.

That means either a histologic (tissue-based) exam of an endometrial biopsy, or a hysteroscopy. In the tissue-based exam, a pathologist looks specifically for stromal plasma cells. This is sometimes confirmed with a marker called CD138 immunohistochemistry (a lab test on tissue samples). In a hysteroscopy, a doctor looks directly inside the uterus with a small camera. Neither test is part of a standard fertility workup by default. If you're being evaluated for unexplained implantation failure, it's worth asking specifically whether either one has been considered.

Who's more likely to get it?

Chronic endometritis has known risk factors worth knowing. This isn't to worry you. It's because they can help decide whether testing makes sense for your history. These include using a contraceptive IUD, a history of multiple pregnancies, previous pregnancy losses or abortions, and a history of abnormal uterine bleeding.

None of these guarantee you have chronic endometritis. Plenty of people with these histories never develop it. But if one or more applies to you, and you're facing unexplained implantation trouble, it's a reasonable thing to bring up with your provider.

Does treatment actually help?

The standard treatment for chronic endometritis is oral doxycycline, 100 mg taken twice a day for 14 days. ASRM guidance frames this as the recommended first treatment once chronic endometritis shows up on a tissue exam. Doctors then follow up with a 'test of cure' biopsy. This confirms whether the treatment actually worked.

If the infection doesn't clear after that first course, doctors use a combined course of ciprofloxacin and metronidazole as a second option. Amoxicillin-clavulanate is available as a limited third option. It's used for cases that still don't resolve.

Here's why this matters so much if you're trying to conceive. One study looked at women having a fresh day-3 embryo transfer. Live birth rates were dramatically higher, roughly 60-65%, in those whose chronic endometritis had been treated. That compares with roughly 6-15% in those left untreated. That's not a small difference. It's the kind of gap that makes chronic endometritis worth ruling out, not brushing off as background noise.

Why does confirming the cure matter?

Taking the antibiotics isn't automatically the end of the story. Patients who finish treatment and then get a negative 'test of cure' biopsy tend to have better outcomes than those who were treated but never had that follow-up biopsy. A negative result means follow-up testing confirms the infection actually cleared.

It's easy to assume a treatment course is complete once the medication schedule ends. But the research suggests the confirmation step itself is part of what makes treatment work in practice. It's not just a formality tacked on at the end.

Frequently asked questions

Sources

1. Chronic endometritis is a mild, persistent inflammation of the endometrium, usually due to microbial colonization, that is defined as lasting 30 days or longer and is not related to pregnancy. — StatPearls (NCBI Bookshelf)
2. Chronic endometritis is often symptomless, and when symptoms do occur they tend to be nonspecific, most commonly abnormal uterine bleeding, pelvic discomfort, and leukorrhea (vaginal discharge). — StatPearls (NCBI Bookshelf)
3. Because chronic endometritis rarely causes clear symptoms and does not show up reliably on standard serum or culture tests, diagnosing it requires either a histologic exam of an endometrial biopsy (looking for stromal plasma cells, sometimes using the CD138 immunohistochemistry marker) or hysteroscopic confirmation. — StatPearls (NCBI Bookshelf)
4. The standard treatment for chronic endometritis is a course of oral doxycycline, 100 mg taken twice a day for 14 days. — StatPearls (NCBI Bookshelf)
5. In a study of women undergoing fresh day-3 embryo transfer, live birth rates were dramatically higher in patients whose chronic endometritis had been treated (roughly 60-65%) compared with those who were untreated (roughly 6-15%). — StatPearls (NCBI Bookshelf)
6. Chronic endometritis has established risk factors including use of a contraceptive intrauterine device (IUD), a history of multiple pregnancies, previous pregnancy losses/abortions, and a history of abnormal uterine bleeding. — StatPearls (NCBI Bookshelf)
7. When chronic endometritis is diagnosed on histology, the recommended first-line treatment is doxycycline, with a follow-up 'test of cure' biopsy; if the infection persists, a combined course of ciprofloxacin and metronidazole is used as second-line treatment, and amoxicillin-clavulanate is a limited third-line option. — ASRM (Fertility & Sterility Journal Club Global)
8. Patients treated for chronic endometritis who achieve a negative 'test of cure' biopsy (confirming the infection has cleared) have better clinical outcomes than those who were treated but never had a follow-up biopsy to confirm resolution. — ASRM (Fertility & Sterility Journal Club Global)