Learn About Causes of Vaginal Bleeding

What Is Vaginal Bleeding and When Is It Normal?

Vaginal bleeding is the discharge of blood from the vagina. For people who menstruate, some vaginal bleeding is a normal part of the monthly cycle. Understanding what counts as normal bleeding helps you recognize when something might need medical attention.

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A typical menstrual period lasts between 3 and 7 days. Most people lose about 2 to 3 tablespoons of blood during their entire period, though some lose up to 5 tablespoons. The blood may be bright red, dark red, or brownish in color. It's normal for the flow to be heavier on the first day or two and lighter toward the end. Many people also experience small blood clots, usually no larger than a quarter.

Menstrual cycles typically occur every 21 to 35 days, though some variation is normal. Younger people who recently started menstruating may have irregular cycles for the first few years. Similarly, people approaching menopause often experience changes in cycle length and flow.

Vaginal bleeding between periods, after sex, or after menopause is considered abnormal and warrants discussion with a healthcare provider. Abnormal bleeding might appear heavier than usual, last longer than normal, or occur at unexpected times. Some people describe abnormal bleeding as soaking through one or more pads or tampons per hour for several hours, or passing blood clots larger than a quarter.

Practical takeaway: Keep a simple record of your periods for a few months, noting the start date, end date, and whether flow is light, moderate, or heavy. This information helps healthcare providers understand your bleeding patterns and identify changes that might need evaluation.

Menstrual Cycle Changes and Hormonal Causes

The menstrual cycle is controlled by hormones, primarily estrogen and progesterone. Changes in these hormone levels directly affect vaginal bleeding patterns. Understanding how hormones influence bleeding helps explain why patterns change at different life stages.

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During the first half of the menstrual cycle (called the follicular phase), estrogen levels rise gradually. This hormone thickens the lining of the uterus, called the endometrium. Around day 14 of a typical 28-day cycle, a surge in a hormone called luteinizing hormone (LH) triggers ovulation, when the ovary releases an egg. After ovulation, progesterone levels rise during the second half of the cycle (the luteal phase). Progesterone stabilizes the uterine lining and prepares the body for pregnancy. If pregnancy doesn't occur, hormone levels drop sharply, triggering the uterine lining to shed. This shedding appears as menstrual bleeding.

When hormone levels are imbalanced, bleeding patterns often change. Polycystic ovary syndrome (PCOS) is a condition where the ovaries produce higher-than-normal levels of androgens, male-type hormones. This hormonal imbalance can prevent ovulation, leading to irregular or absent periods, or sometimes heavy bleeding when periods do occur. PCOS affects about 1 in 10 women of reproductive age, according to the Centers for Disease Control and Prevention.

Thyroid disorders also affect menstrual bleeding. An overactive thyroid (hyperthyroidism) can cause lighter, shorter periods or skipped periods. An underactive thyroid (hypothyroidism) may result in heavier, longer periods. Thyroid problems are relatively common, particularly in women, making thyroid function worth checking if bleeding patterns change significantly.

Hormonal birth control methods work by altering natural hormone levels. Combined oral contraceptives contain estrogen and progestin and typically result in lighter periods or no bleeding at all. Progestin-only methods, like the hormonal IUD or the implant, also often reduce bleeding. These changes are expected and usually not concerning.

Practical takeaway: If your menstrual bleeding has changed noticeably—becoming much heavier, lighter, or more irregular—mention this to your healthcare provider. They can check whether hormonal changes, thyroid issues, or other factors are involved.

Structural Problems in the Uterus and Reproductive Tract

Physical structures within the uterus and reproductive tract can cause or contribute to abnormal vaginal bleeding. These structural issues range from benign (non-cancerous) growths to anatomical variations present from birth.

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Uterine fibroids are benign tumors that grow in or on the uterus. They are quite common, occurring in 70 to 80 percent of women by age 50, though not all cause symptoms. When fibroids develop in specific locations or grow large, they can cause heavy menstrual bleeding, prolonged periods, or bleeding between periods. Some people with fibroids also experience pelvic pain or pressure. Fibroids vary greatly in size and number, and some may shrink or stop growing on their own.

Uterine polyps are small, benign growths on the inner lining of the uterus. They occur more frequently as people age and are found in about 7 to 15 percent of women undergoing fertility evaluation. Polyps can cause heavy periods, bleeding between periods, or bleeding after menopause. Unlike fibroids, polyps are usually small and can sometimes be removed during a simple office procedure.

Adenomyosis occurs when tissue from the uterine lining grows into the muscle layer of the uterus. This causes the uterus to become thickened and enlarged, often resulting in heavy, prolonged periods and severe menstrual cramping. Adenomyosis is more common in people over 40 and those who have had pregnancies, though it can occur at any reproductive age.

Endometrial hyperplasia is a thickening of the uterine lining caused by excess estrogen without enough progesterone. It can cause heavy or prolonged bleeding. While usually benign, some forms of hyperplasia carry a small risk of developing into cancer, making evaluation and monitoring important. Endometrial hyperplasia often occurs in people with obesity, diabetes, or those taking certain medications like tamoxifen for breast cancer treatment.

Scarring of the uterus, called Asherman's syndrome, can occur after procedures like dilation and curettage (D&C) or after treating uterine infections. This scarring may result in lighter periods, absent periods, or no menstrual bleeding at all, despite normal hormone levels.

Practical takeaway: If you have heavy periods, particularly with pelvic pain or pressure, or if your bleeding pattern changes without an obvious reason, ask your healthcare provider about structural causes. Imaging tests like ultrasound can often identify fibroids, polyps, or other growths.

Infections and Inflammatory Conditions

Infections and inflammatory conditions in the reproductive tract can trigger abnormal vaginal bleeding. These range from sexually transmitted infections to non-infectious inflammatory conditions. Recognizing these causes is important because they often require specific treatment.

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Pelvic inflammatory disease (PID) occurs when bacteria spread from the cervix to the upper reproductive organs including the uterus, fallopian tubes, and ovaries. PID is often caused by sexually transmitted bacteria like chlamydia or gonorrhea, though other bacteria can be involved. According to the CDC, about 1 million cases of PID occur each year in the United States. Symptoms of PID include abnormal vaginal bleeding or bleeding between periods, pelvic pain, painful intercourse, and vaginal discharge. PID requires antibiotic treatment to prevent serious complications like infertility or chronic pelvic pain.

Cervicitis, inflammation of the cervix, can be caused by infections including herpes simplex virus, chlamydia, gonorrhea, or other bacteria. Cervicitis may cause abnormal vaginal bleeding, vaginal discharge, or pain during intercourse. Some cases resolve on their own, while others require treatment depending on the underlying cause.

Endometritis is inflammation of the uterine lining, usually caused by bacterial infection. It can occur after childbirth, miscarriage, or certain gynecological procedures. Symptoms include abnormal bleeding, fever, pelvic pain, and unusual vaginal discharge. Endometritis typically requires antibiotic treatment.

Vaginitis, inflammation of the vagina, can result from infections (bacterial v