PMB stands for postmenopausal bleeding. It refers to any vaginal bleeding that occurs after a woman has gone 12 consecutive months without a period, marking the completion of menopause. While PMB is often caused by something harmless, it always requires medical evaluation because roughly 9% of cases turn out to be endometrial cancer (cancer of the uterine lining).
Why PMB Is Taken Seriously
Once you’ve passed the 12-month mark without a period, any new vaginal bleeding is considered abnormal. That includes light spotting, pink or brown discharge, and heavier bleeding. The concern isn’t that cancer is the most likely cause, because it isn’t. The concern is that endometrial cancer is common enough in this group that it can’t be ruled out without testing.
A large meta-analysis pooling data from 92 studies found that the overall risk of endometrial cancer among women with PMB was 9%, though the number varied by region and whether someone was using hormone therapy. Women on hormone therapy had a lower pooled risk (around 7%), while those not using it had a risk closer to 12%. That means the vast majority of women with PMB, roughly 9 out of 10, have a non-cancerous explanation. But 1 in 10 is not a number doctors are comfortable ignoring.
Common Causes of PMB
Most postmenopausal bleeding stems from benign conditions:
- Vaginal or endometrial atrophy: After menopause, dropping estrogen levels cause the vaginal walls and uterine lining to thin and become fragile. This is the single most common cause of PMB. Even minor friction or dryness can trigger light bleeding.
- Endometrial polyps: Small, usually noncancerous growths on the uterine lining. They can develop at any age but become more common after menopause and often cause irregular spotting.
- Endometrial hyperplasia: A thickening of the uterine lining, sometimes caused by excess estrogen without enough progesterone to balance it. Certain types of hyperplasia carry a higher risk of eventually progressing to cancer.
- Hormone therapy: Women taking estrogen or combined hormone therapy for menopausal symptoms may experience breakthrough bleeding, especially in the first several months of treatment or after dose changes.
- Endometrial cancer: While it accounts for a minority of PMB cases overall, it remains the most important diagnosis to rule out.
Risk Factors That Raise Concern
Certain factors increase the likelihood that PMB is related to something more serious. Obesity is one of the strongest risk factors for endometrial cancer because fat tissue produces estrogen, which stimulates the uterine lining to grow. Smoking, a history of taking estrogen without progesterone (called unopposed estrogen), and recurrent episodes of PMB also raise the level of concern. If any of these apply to you, your doctor is more likely to move directly to a tissue biopsy rather than starting with imaging alone.
How PMB Is Evaluated
The standard first step is either a transvaginal ultrasound or an endometrial biopsy. You typically don’t need both at the same time.
A transvaginal ultrasound measures the thickness of your uterine lining. The key number here is 4 millimeters. If the lining measures 4 mm or less, the chance of endometrial cancer is extremely low, with a negative predictive value above 99%. In practical terms, that means a thin lining on ultrasound is very reassuring. No further testing is needed in most cases.
If the lining is thicker than 4 mm, or if the ultrasound can’t get a clear view, the next step is an endometrial biopsy. This is a quick office procedure where a thin instrument is passed through the cervix to collect a small sample of the uterine lining. The tissue is then examined under a microscope. It’s the most direct way to check for cancer or precancerous changes.
For women with risk factors for endometrial cancer or who have had repeated episodes of PMB, biopsy is typically recommended as the very first test, even before ultrasound. The reasoning is straightforward: these women need a tissue diagnosis, and imaging alone can’t provide one.
When Initial Tests Aren’t Enough
Sometimes a standard biopsy doesn’t capture enough tissue, or the bleeding keeps coming back even after a normal ultrasound or biopsy result. In these situations, a procedure called hysteroscopy may be recommended. This involves inserting a thin camera into the uterus, allowing the doctor to directly see the lining and any growths like polyps. The advantage is that small polyps or other focal lesions that a blind biopsy might miss can be seen and removed at the same time.
Hysteroscopy combined with dilation and curettage (D&C) is considered the gold standard for evaluating PMB when simpler tests fall short. It’s both diagnostic and therapeutic, meaning a polyp causing your bleeding can be identified and removed in a single procedure. This is particularly relevant because blind biopsy instruments can sometimes slide past small growths without sampling them.
What PMB Feels Like
PMB can range from a faint pink or brown stain on underwear to heavier, period-like bleeding. Some women notice it only once, while others have recurring episodes over weeks or months. The amount of bleeding doesn’t reliably indicate the cause. A single episode of light spotting can still warrant evaluation, and heavy bleeding can turn out to be from a benign polyp. The defining feature isn’t the volume or color. It’s the timing: any bleeding after menopause is complete counts as PMB, no matter how minor it seems.
Women on hormone therapy sometimes find it harder to know whether their bleeding is a normal side effect of treatment or something that needs separate evaluation. As a general rule, unexpected bleeding that occurs after the first few months of a stable hormone therapy regimen, or any bleeding that changes in pattern, should be assessed the same way as PMB in someone not on hormones.