Ovulation occurs each time a woman’s ovary releases a mature egg during the menstrual cycle. It usually takes place around two weeks, or midway, into the cycle. Ovulation bleeding is non-menstrual bleeding. It can occur immediately before or after ovulation for a variety of reasons, but it does not usually indicate a serious issue. Around 5% of women experience ovulation bleeding.

Identifying ovulation bleeding

This type of bleeding is a much lighter flow and is a different color than what occurs during regular menstruation. It usually continues for a couple of days. The lighter pink color is due to a higher level of cervical fluid mixing with the blood. It may also be brownish-red. Some women also experience mild abdominal cramps during this phase of their cycle.

Implantation and early pregnancy bleeding

Ovulation bleeding can be a sign of pregnancy. Soon after the sperm fertilizes an egg, the egg must implant itself in the uterine lining. Generally, this occurs about 10 days after ovulation. Some women experience light spotting during this time. Additionally, some have light bleeding in the earliest stages of pregnancy. In most cases, it is a harmless sign and stops on its own without medical intervention.

Low Progesterone Levels

The two female sex hormones, progesterone and estrogen, influence the production and shedding of a woman’s endometrial lining in the uterus. Luteinizing hormone (LH) helps control the menstrual cycle and triggers ovulation. Just before ovulation occurs, LH and progesterone levels rise. A lack of ovulation is usually due to insufficient levels of progesterone. This inhibits the shedding of the endometrial lining and may result in bleeding.

Sudden Drops in Estrogen Levels

Estrogen causes the uterine lining to thicken. An abrupt drop in estrogen levels leads to a thinning out of this lining, and the tissue starts to shed. The regular monthly menstrual cycle flushes out the endometrial lining, but lowered estrogen levels may lead to leaking and an unstable lining. Intermenstrual bleeding, spotting, or delayed periods can result.

Hypothalamic Causes

The hypothalamus is the area of the brain that produces hormones that control heart rate, body temperature, mood, hunger, thirst, and several other functions. The pituitary and other glands release these hormones. A hormonal imbalance can lead to anovulation, an absence or lack of ovulation that results in bleeding. Research shows that stress, eating disorders, weight, and excessive exercise can cause this type of anovulation and ovulation bleeding.

Endocrine Issues

The thyroid gland is a butterfly-shaped gland at the base of the front of the neck. Hypothyroidism — when the thyroid does not produce enough thyroid hormones — and hyperthyroidism — an overproduction of thyroid hormone — are possible reasons why premenopausal women experience ovulation bleeding.

Polycystic Ovary Syndrome (PCOS)

Abnormal bleeding during ovulation in premenopausal women in their late teens or early 20s may be due to polycystic ovary syndrome, an enlargement in the ovaries and their follicles. Research suggests that PCOS is more prevalent in women with obesity and those who have excess levels of androgen, a male hormone.

Mittelschmerz

During ovulation, some women experience dull pain on the side of the body where the ovary is releasing the egg. This usually occurs about two weeks before their upcoming menstrual period. The pain, mittelschmerz, may switch sides from one month to the next and its cause is unknown. A heavier-than-normal discharge and vaginal bleeding may occur as well.

Cervical abnormalities

Polyps or fibroid growths in the uterus can cause bleeding, as can cervical dysplasia, the abnormal growth of cells on the surface of the cervix caused by Human Papillomavirus (HPV). Women who experience spotting should keep track of the dates to determine if it is occurring during ovulation or at another point in their menstrual cycle.

Oral Contraceptives

If mid-cycle bleeding occurs and the woman is taking oral contraceptives (OCs), it is unlikely the bleeding is due to ovulation. Breakthrough bleeding or a more disorderly bleeding pattern is common in the first few months of starting OCs because the medication causes changes in the thickness of the endometrium and a breakdown of surface vessels.