Endometritis is an infection or inflammation of the endometrium, the tissue lining the inside of your uterus. It develops when bacteria travel up through the cervix and colonize the uterine lining, triggering an immune response that can cause pelvic pain, abnormal bleeding, or sometimes no noticeable symptoms at all. The condition comes in two forms, acute and chronic, and each behaves quite differently in terms of symptoms, duration, and impact on fertility.
Acute vs. Chronic Endometritis
Acute endometritis refers to an infection lasting 30 days or less. It tends to come on suddenly, with pelvic pain, painful intercourse, and vaginal discharge. Depending on severity, you may also develop fever and general fatigue, though these systemic symptoms are often absent in milder cases. Under a microscope, the uterine tissue shows tiny pockets of infection and an influx of white blood cells called neutrophils, the body’s first responders to bacterial invasion.
Chronic endometritis is a lower-grade inflammation lasting 30 days or longer. It’s caused by ongoing bacterial colonization of the uterine lining rather than a single acute infection. Many people with chronic endometritis have no symptoms at all. When symptoms do appear, they tend to be vague: irregular or abnormal uterine bleeding, mild pelvic discomfort, and a whitish vaginal discharge. The hallmark under the microscope is the presence of plasma cells (a type of immune cell normally not found in the uterine lining), along with tiny polyps less than 1 mm in size and swelling in the tissue.
What Causes It
Most cases are caused by common bacteria that normally live in the vagina or gastrointestinal tract. In a study of 142 women with chronic endometritis, common bacteria like E. coli, Enterococcus, and various Streptococcus and Staphylococcus species accounted for about 78% of infections. Mycoplasma and Ureaplasma were found in roughly 25% of cases, and Chlamydia in about 13%. Sexually transmitted infections like chlamydia and gonorrhea are more commonly linked to acute endometritis, particularly in sexually active individuals.
The uterus is normally well protected by the cervix, which acts as a physical and immunological barrier. Anything that disrupts that barrier can allow bacteria in. Common risk factors include:
- Childbirth, especially after prolonged labor, membrane rupture, or cesarean delivery (which carries over 20 times the risk compared to vaginal delivery)
- Miscarriage or abortion
- Uterine procedures such as dilation and curettage (D&C), endometrial biopsy, or hysteroscopy
- IUD insertion
Symptoms to Recognize
The tricky part of endometritis, especially the chronic form, is that it can be nearly silent. Acute endometritis is more straightforward: you’ll typically notice a relatively sudden onset of pelvic pain, discharge that may look or smell unusual, and pain during sex. Some people develop a low-grade fever, though many don’t.
Chronic endometritis is harder to spot. The most common complaint is abnormal uterine bleeding, which might mean heavier periods, bleeding between periods, or spotting after sex. Mild, persistent pelvic discomfort is another clue. Because these symptoms overlap with so many other conditions, chronic endometritis often goes undiagnosed for months or longer, sometimes only discovered during a fertility workup.
How It’s Diagnosed
Diagnosing endometritis usually requires more than just a physical exam. A transvaginal ultrasound can provide useful clues. Two specific signs on ultrasound, a dark rim beneath the uterine surface and blurring of the boundary between the uterine lining and muscle wall, have a combined sensitivity of about 81% and specificity of 92% when both are present. That means ultrasound catches most cases, but not all.
The gold standard for chronic endometritis is an endometrial biopsy. A small tissue sample is taken from the uterine lining and examined for plasma cells using a staining technique that highlights a specific marker called CD138. Finding five or more of these cells per high-power microscope field is one widely used threshold for diagnosis. Research shows that women meeting this cutoff have significantly lower live birth rates and higher pregnancy loss rates compared to women with fewer or no plasma cells, making accurate diagnosis particularly important for anyone trying to conceive.
The Connection to Fertility
Chronic endometritis has become an increasingly recognized factor in unexplained infertility, failed IVF cycles, and recurrent miscarriage. About 15% of women undergoing IVF have chronic endometritis, but the prevalence jumps to 42% among women with repeated implantation failure. Among women who have experienced three or more pregnancy losses, the rate may be as high as 58%.
The inflammation disrupts the delicate immune environment the uterine lining needs to accept and support an embryo. Immune cells, antibodies, and signaling molecules in an inflamed endometrium can interfere with the early stages of implantation and the growth of the tissue that eventually forms the placenta.
The encouraging news is that treatment makes a meaningful difference. One prospective study found that the per-pregnancy live birth rate in women with recurrent pregnancy loss and chronic endometritis increased from 7% before antibiotic treatment to 56% afterward. In another study, implantation rates nearly quadrupled after treatment (from about 5% to 19%). Women whose uterine lining returned to a normal appearance on follow-up examination after treatment had significantly better pregnancy outcomes than those whose tissue still showed signs of inflammation.
Treatment and Recovery
Endometritis is treated with antibiotics. Acute endometritis, especially postpartum cases or severe infections, may require intravenous antibiotics in a hospital setting until fever resolves, followed by oral antibiotics at home. Milder acute cases and chronic endometritis are typically managed with a course of oral antibiotics lasting one to two weeks, targeting the specific bacteria identified or covering the most common culprits.
After completing antibiotics for chronic endometritis, many specialists recommend a follow-up biopsy to confirm the infection has cleared, particularly for women planning pregnancy or undergoing fertility treatment. If the first round of antibiotics doesn’t eliminate the plasma cells, a second course with different medications is usually tried. Most cases resolve with treatment, and once the inflammation clears, the uterine lining can return to normal function.
What Happens if It’s Left Untreated
Endometritis is part of a broader spectrum of pelvic inflammatory disease (PID), which can also involve the fallopian tubes, ovaries, and surrounding tissue. Untreated infection can spread beyond the uterus, leading to tubo-ovarian abscesses or pelvic peritonitis. Even mild or seemingly asymptomatic PID can cause scarring that leads to infertility, chronic pelvic pain, or increased risk of ectopic pregnancy. Delays in diagnosis and treatment increase the likelihood of these long-term consequences, which is why persistent pelvic symptoms or unexplained fertility problems warrant thorough evaluation.