Ovulation bleeding is vaginal bleeding during or immediately before or after ovulation, which occurs roughly in the middle of a menstrual cycle.

Changes in estrogen levels are often the cause of this type of bleeding, and light spotting around ovulation does not usually signal a serious problem. Some people refer to ovulation bleeding as "estrogen breakthrough bleeding."

In this article, learn more about ovulation bleeding and other types of bleeding between periods. We also explain when to see a doctor.

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Hormonal changes during ovulation may cause bleeding that is much lighter than a regular period.

Ovulation bleeding generally refers to bleeding that occurs around the time of ovulation, which is when the ovary releases an egg.

In the days leading up to ovulation, estrogen levels steadily rise. After the release of an egg, the estrogen levels dip, and progesterone levels begin to increase.

This shift in the balance between estrogen and progesterone levels can cause light bleeding, which is usually much lighter than a regular period.

In most cases, it does not cause any other symptoms.

If a person experiences other symptoms, such as cramping, alongside the bleeding or it lasts longer than a few days, something other than ovulation bleeding may be the underlying cause.

People who do not regularly ovulate may have unusual bleeding patterns, such as bleeding very lightly for many days or only getting a period every few months. Numerous medical conditions, including polycystic ovary syndrome (PCOS) and endometriosis, can cause irregular cycles.

Ovulation bleeding is just one of many types of atypical vaginal bleeding. While bleeding that relates to ovulation is usually harmless, it is important to ensure that there is no underlying medical cause.

Some hallmarks of bleeding during ovulation include:

  • The bleeding happens around ovulation. On average, ovulation occurs 14 days after the last period began, although many people ovulate earlier or later. People can use ovulation testing kits or monitor their basal body temperature to help pinpoint the time of ovulation.
  • The bleeding occurs only once during each month at around the same time.
  • The bleeding stops on its own within a couple of days and is not heavy or painful.

Bleeding that does not follow this pattern could be due to:

  • Implantation bleeding. After a sperm fertilizes an egg, the egg must implant in the lining of the uterus. Implantation usually occurs about 10 days after ovulation. Some people experience light spotting, called implantation bleeding, around this time.
  • Pregnancy-related bleeding. Bleeding early in pregnancy is common, and it can be due to a number of causes, ranging from a relatively harmless condition called a subchorionic hemorrhage to a potentially life-threatening ectopic pregnancy.
  • Anovulatory cycles. Anovulatory cycles are monthly cycles during which a person does not ovulate. A wide range of medical conditions can cause a person not to ovulate. Irregular bleeding is common during an anovulatory cycle.
  • Structural abnormalities. Structural problems with the uterus or ovaries may cause unusual bleeding. For example, a person with endometriosis or uterine polyps may bleed between cycles.
  • Kidney or liver disease. Kidney failure and liver disease may cause problems with blood clotting, leading to abnormal bleeding.
  • Thyroid issues. The thyroid releases hormones that help regulate the menstrual cycle. Too much or too little thyroid hormone can cause bleeding between periods.
  • Hormone treatments. Various hormones, including birth control pills and fertility drugs, may cause bleeding between cycles.
  • Drugs and medications. Some prescription medications, such as anticonvulsants and antipsychotics, can cause abnormal bleeding.
  • Pituitary diseases. The pituitary gland helps regulate hormones that affect the menstrual cycle, including estrogen and progesterone. Conditions that affect the pituitary gland, such as Cushing's disease, may cause unusual bleeding.
  • Infection. Sexually transmitted infections, such as gonorrhea or chlamydia, may cause the cervical tissue to become inflamed and bleed easily.
  • Tumors. Ovarian tumors, especially those that produce estrogen, may cause unusual bleeding. Although rare, abnormal bleeding may be a symptom of cervical or endometrial cancer.

In people with very irregular cycles, it can be difficult to tell the difference between irregular bleeding and the normal monthly period. Anyone whose periods do not follow a predictable pattern should talk to a doctor.

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A person should seek medical advice if bleeding patterns are different than usual.

Light spotting in the middle of the cycle is not usually harmful, especially if it occurs at the same time each month.

However, it is important to discuss any unusual bleeding with a doctor, particularly if other symptoms occur alongside it. Charting the bleeding — including what time it usually occurs and how long it lasts — can help a doctor identify the cause.

People who experience the following should speak to a doctor:

  • changes in the usual pattern of bleeding, for example, periods being less than 21 days or more than 35 days apart
  • bleeding becoming much heavier or lighter than usual
  • excessive bleeding, such as soaking a tampon or pad every 2 hours or passing large blood clots
  • additional symptoms, such as painful periods, difficulty getting pregnant, pelvic pain during or after sex, shortness of breath, lightheadedness, dizziness, or chest pain
  • bleeding after menopause

A person should seek urgent medical attention if:

  • they have had a positive pregnancy test or believe that they are pregnant
  • the bleeding is extremely heavy, soaking through a large pad or tampon every hour
  • they develop a fever or other symptoms of an infection
  • they have a bleeding disorder and experience heavy bleeding that does not stop

Bleeding between periods is common, affecting 9–14% of females between menarche — when periods begin — and menopause.

While ovulation bleeding is a common reason for bleeding between periods, it is not the only potential cause. Therefore, it is important to monitor the bleeding and talk to a doctor about any bothersome symptoms.

As everyone's menstrual cycle can be different, a person may wish to track their cycle to determine the usual cycle length and the typical day of ovulation. This information can often help a doctor determine whether ovulation or something else is causing the bleeding.