Many different things can cause a short period, and an occasional period that ends early is likely not cause for concern. However, if a person’s normal cycle suddently becomes shorter, it may indicate an underlying health condition.

A typical menstrual flow lasts 3–5 days, but cycles as short as 1 day and as long as 8 days are considered normal.

Sometimes, an individual may have brief spotting, or light bleeding, at a time of the month when they do not normally bleed. This may be implantation bleeding, a normal sign of early pregnancy that happens when the fertilized egg implants in the uterus.

However, in some cases, irregular bleeding may indicate a condition such as endometriosis or polycystic ovary syndrome (PCOS).

Read more to learn about the possible causes of a short period, when to contact a doctor, and more.

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Each person’s menstrual flow varies in length and frequency. Doctors consider flows within the range of 3–5 days normal.

The typical amount of blood lost is 30 milliliters, which equates to about 1/8 of a cup. However, heavier and lighter bleeding are generally normal if they are consistently a person’s usual flow.

If a person has a short cycle, they should ask themselves: “Is this normal for me?”

When a person’s cycles are normally short, it is likely nothing to be worried about. However, if it is unusual, or a person has other sudden changes in their period, they may want to contact a doctor.

There are many causes of a short or light period. The following conditions and occurrences may cause either a short cycle or light bleeding that may be mistaken for a short period.

Pregnancy

Some people have spotting during pregnancy, which they may mistake for a short period. This does not necessarily suggest a problem during the early stages of pregnancy, as 15–25% of pregnant people bleed during the first trimester.

Spotting or light bleeding may occur 1–2 weeks after fertilization when the egg attaches to the uterine lining. This is called implantation bleeding.

Additionally, it is not uncommon to have light cervical bleeding during early pregnancy. Because more blood vessels are developing in this area, light spotting can occur.

Pregnancy loss

Pregnancy loss is relatively common, happening in up to 26% of pregnancies. Although bleeding can be normal during pregnancy, it may sometimes indicate a problem.

If bleeding occurs early in a person’s pregnancy, it can indicate pregnancy loss. This may start as light spotting, but usually gets heavier. A person experiencing a pregnancy loss may also have painful abdominal cramps and tissue discharge.

Symptoms of pregnancy loss may include:

  • mild to severe back pain
  • painful contractions every 5–20 minutes
  • white-pink mucus discharge
  • clot-like tissue discharge

In some cases, an ectopic pregnancy can cause bleeding. This is when the fertilized egg implants outside the uterus, usually in a fallopian tube. If the fallopian tube ruptures, it can cause bleeding and severe pain. People experiencing this should seek immediate medical attention.

Perimenopause

Perimenopause refers to the years leading up to menopause, which is when a menstruating person stops having monthly periods. Perimenopause usually begins when a person is in their 30s or 40s.

During perimenopause, the ovaries produce varying amounts of the hormone estrogen, which causes menstrual cycle changes. It can make a person’s cycle longer or shorter and make their flow lighter or heavier. Additionally, it can cause a person to skip periods.

Other perimenopause symptoms may include:

Anovulatory cycle

An anovulatory cycle happens when a menstruating person’s ovaries do not release an egg. This can cause irregular and heavy bleeding. It is common in young people who have just started menstruating and perimenopausal individuals. When the ovaries do not release an egg, it may cause bleeding due to changes in hormone levels.

Symptoms of an anovulatory cycle include:

PCOS

According to the Office on Women’s Health, PCOS is a hormone imbalance affecting 1 in 10 females of childbearing age. It occurs when a hormonal imbalance prevents the ovaries from developing or releasing monthly eggs.

PCOS can cause infertility and the growth of benign cysts on the ovaries.

Symptoms of PCOS may include:

Endometriosis

Endometriosis happens when endometrial tissue — similar to the uterine lining — grows outside the uterus. It is relatively common, affecting more than 11% of females in the United States aged 15–44.

The tissue usually grows in the pelvic area, often on the ovaries, fallopian tubes, and around the uterus. It may also grow in the vagina, bowels, bladder, rectum, and cervix.

During a person’s menstrual cycle, this endometrial tissue swells and bleeds like the uterine lining. This can cause severe menstrual cramps as well as irregular and heavy bleeding.

Other symptoms include:

Birth control

People who use birth control may experience breakthrough bleeding, which is a small amount of bleeding when they are not expecting their monthly period.

This can happen with the use of any type of birth control, but occurs more often with:

Temporary reduction in fertility

Bleeding that occurs outside of menstruation is called intermenstrual bleeding. According to a 2016 study, this is common. Doctors believe hormone imbalances or structural abnormalities, like benign growths, cause this bleeding.

The study authors analyzed data from the menstrual cycle of 549 females to see whether there was a link between intermenstrual bleeding and infertility. They found that there was a connection — people with intermenstrual bleeding were less likely to get pregnant during that menstrual cycle.

However, the bleeding did not affect their chances of becoming pregnant in future cycles. This means that if a person has infrequent intermenstrual bleeding, it likely does not affect their overall fertility. However, if a person frequently has this bleeding, they may want to contact a doctor, as there may be an underlying cause.

Individuals should contact a doctor if they experience:

  • periods that become irregular after being regular
  • periods that occur less than every 38 days or more than every 24 days
  • menstrual blood flow that contains blood clots larger than a quarter
  • pelvic pain when they are not menstruating
  • bleeding when they are not menstruating
  • particularly heavy bleeding
  • skipping a period for three months

A short menstrual flow is usually not a cause for concern if that is a person’s average cycle time. However, if this is a change from their normal cycles, there may be an underlying cause.

Many conditions and occurrences can cause a short period of bleeding. Pregnancy, pregnancy loss, endometriosis, anovulatory bleeding, and PCOS can all cause short spells of bleeding that people may mistake for a period.

A person may want to contact a doctor if their periods suddenly become irregular after being regular, they experience pain or bleeding when they are not menstruating, or they have particularly heavy bleeding.