Abnormal vaginal bleeding is any vaginal bleeding unrelated to normal menstruation. This type of bleeding may include spotting of small amounts of blood between periods — often seen on toilet tissue after wiping — or extremely heavy periods in which you soak a pad or tampon every one to two hours for two or more hours.

Normal vaginal bleeding, or menstruation, occurs every 21 to 35 days when the uterus sheds its lining, marking the start of a new reproductive cycle. A menstrual period may last for just a few days or more than a week. Your flow may be heavy or light and still considered normal. Cycles tend to be longer before age 20 and after age 40, and your flow may be heavier at those ages.

Possible causes of abnormal vaginal bleeding include:

1. Adenomyosis
2. Celiac disease
3. Cervical cancer
4. Cervical polyps, noncancerous (benign) growths on your cervix
5. Chlamydia
6. Problems with the cervix, such as a cervical infection, inflamed cervix or growths on the cervix
7. Endometrial cancer
8. Endometrial hyperplasia
9. Endrometrial polyps
10. Endometritis
11. Fluctuating hormone levels
12. Gonorrhea
13. Hypothyroidism (underactive thyroid)
14. Hyperthyroidism (overactive thyroid)
15. Intrauterine contraceptive device
16. Menorrhagia
17. Miscarriage (before the 20th week) or intrauterine fetal death
18. Ovarian cancer
19. Ovarian cysts
20. Pelvic inflammatory disease (PID)
21. Perimenopause
22. Polycystic ovary syndrome (PCOS)
23. Pregnancy
24. Random ovulatory cycles
25. Severe systemic disease, such as kidney or liver disease
26. Sexual abuse
27. Sexual intercourse
28. Stopping birth control pills or hormone replacement therapy (withdrawal bleeding)
29. Tamoxifen side effect
30. Thrombocytopenia
31. Uterine fibroids
32. Uterine polyps
33. Uterine sarcoma
34. Vaginal atrophy
35. Vaginal cancer
36. Vaginal or cervical trauma
37. Vaginitis
38. Von Willebrand disease (and other blood clotting disorders)

Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.

Source: mayoclinic.org

In general, anytime you experience unexpected vaginal bleeding, consult your doctor. Whether or not vaginal bleeding is normal depends on your age and the circumstances.

You should contact your doctor in the following situations:

• Postmenopausal women not taking hormone therapy should see a doctor if they experience vaginal bleeding.
• Postmenopausal women taking cyclic hormone therapy may experience some vaginal bleeding. A cyclic hormone therapy regimen — oral estrogen daily plus oral progestin for 10 to 12 days a month — can lead to bleeding that resembles a period (withdrawal bleeding) for a few days out of the month. If you have bleeding other than expected withdrawal bleeding, contact your doctor.
• Postmenopausal women taking continuous hormone therapy — a low-dose combination of estrogen and progestin daily — may experience light, irregular bleeding for the first six months. If bleeding persists longer or heavy bleeding begins, see your doctor.
• Girls who don't have any other signs of puberty or are younger than age 8 should have any vaginal bleeding investigated.

The following situations are likely normal, but talk to your doctor if you are concerned:

• Newborn girls may have some vaginal bleeding during the first month of life. Bleeding that's excessive or lasts longer should be checked out.
• Teenagers who have just begun having periods may experience irregular cycles during the first few years. In addition, many girls and women have light spotting for a few days before menstruating.
• Women starting birth control pills may experience occasional spotting the first few months.
• Women nearing menopause (perimenopause) may experience increasingly heavy or irregular periods. Ask your doctor about possible treatments to minimize your symptoms.

Source: mayoclinic.org