Having irregular periods can make it harder to predict ovulation, recognize signs of fertility, and time sex accordingly.

Also, unexpected or unusual bleeding may stem from an underlying condition, such as polycystic ovary syndrome (PCOS), which can limit fertility. Anyone concerned about this should contact a doctor.

Below, learn what qualifies as “irregular,” what causes irregular periods, and how they can affect fertility. We also explore ways to boost fertility.

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The menstrual cycle is the time between the start of one period and the next.

An older study, from 2009, tracked the cycles of 167 women who were trying to get pregnant. They found that in healthy women, the menstrual cycle typically varies by about 2.9 days each year.

This means that it would be normal to have a 27-day cycle one month, a 29-day cycle the next month, and a 26-day cycle the following month.

The study cited earlier findings that typical cycles usually varied by around 5 days. The researchers concluded that “normal” variation is 0.3–9 days.

A doctor may consider a person to have irregular periods if the length of their cycle varies by at least 7–9 days. Or, the doctor may consider periods to be irregular if cycles are shorter than 24 days or longer than 38 days.

Sometimes, people with very long cycles do not ovulate. These are called anovulatory cycles, and they can keep a person from receiving accurate results from ovulation monitoring and some fertility tests.

Irregular periods can make it harder to predict ovulation, recognize signs of fertility, and time intercourse accordingly.

In some people, irregularity stems from a medical condition that limits fertility. Or, it may be a sign of approaching menopause.

Below, learn why periods may be irregular.

Dieting and stress

Some diets can cause a person to stop ovulating, and eating disorders can have the same effect. As a result, periods may disappear or become very irregular.

Also, some people find that significant stress keeps them from menstruating.

In most cases, periods return when stress levels reduce and the person has a healthful diet.

Hormone imbalances

A number of hormone disorders can cause a person to ovulate infrequently or not at all.

One of the most common, PCOS, causes problems with the development of eggs, as well as other issues.

PCOS is treatable, and the best approach depends on whether the person wants to become pregnant. If so, the doctor may give them drugs to encourage ovulation. If not, hormonal contraceptives may ease some symptoms.

Other issues that can disrupt hormone levels, ovulation, and the regularity of the menstrual cycle include thyroid disorders, uncontrolled diabetes, and some medications.


Breastfeeding may suppress ovulation, causing very irregular periods. Fertility usually returns when nursing becomes less frequent or ends.

It is worth noting, however, that ovulation can occur during breastfeeding even if cycles have not resumed, so contraception may be necessary. Anyone following the lactational amenorrhea method should do so extremely carefully.


Endometriosis is a disorder that causes uterine tissue, called endometrial tissue, to grow beyond the uterus. This may cause pain and irregular bleeding. A person may bleed between periods, have very heavy periods, or pass blood clots.

Endometriosis can make it difficult for a fertilized egg to implant in the uterus. It can also damage the ovaries and fallopian tubes, affecting ovulation.

While many people with endometriosis can become pregnant, this condition is a leading cause of infertility.


As a person nears menopause, their periods become increasingly irregular. As the ovaries stop producing eggs, periods stop altogether.

People in their 40s or 50s who start having irregular periods may be approaching menopause.

Premature ovarian insufficiency

Premature ovarian insufficiency causes a person to stop producing eggs earlier than usual, often in their 20s or 30s.

If a person wants to become pregnant, a doctor may recommend using a donor egg.

Other issues

Some less likely reasons that periods are irregular include:

  • a ruptured ovarian cyst causing bleeding between periods
  • medications that affect the menstrual cycle
  • ovarian or uterine cancer

Anyone with irregular periods who wants to become pregnant should consult a doctor, such as a fertility specialist. A treatable medical condition may be causing the irregularity.

Meanwhile, a number of strategies can increase the chances of pregnancy:

  • Use a home ovulation monitor to detect luteinizing hormone: Levels usually rise right before ovulation, and a person can plan sex during this surge.
  • Monitor vaginal discharge: Also called cervical fluid, this usually becomes very watery or has the consistency of egg whites right before ovulation.
  • Monitor fertility signs over several months: These patterns and signs are different for everyone.

Anyone who notices no signs of ovulation should consult a doctor, who may prescribe medication to help the body ovulate.

Boosting overall health can also help support fertility. Some strategies include:

  • quitting smoking
  • reducing or eliminating alcohol
  • getting plenty of exercise
  • having a healthful, varied diet
  • maintaining a healthy weight
  • taking a prenatal vitamin containing folic acid

People who have very long cycles may worry about becoming pregnant without realizing it.

Also, spotting is common in early pregnancy, so light bleeding does not necessarily mean that a person is getting their period. The only way to know for sure is to take a pregnancy test.

However, it takes a few days after implantation for a test to return a correct positive result. Implantation is the moment when the fertilized egg embeds in the uterus and pregnancy begins.

Taking this into account, a negative result could indicate that the person simply took the test a few days too early. Anyone who is unsure when or whether they are ovulating might consider testing every week or so.

Pregnancy is not usually a medical emergency. Unless a person has heavy bleeding or a history of ectopic pregnancy, there may be no need to see a doctor right away.

However, receiving early prenatal care may increase the likelihood of a healthy pregnancy, so it may be a good idea to see a healthcare provider within the first few weeks.

They may make recommendations about healthful eating and other important ways to support the health of the pregnancy.

A person who wants an abortion should contact a doctor as soon as possible, because there are more options in early pregnancy.

Anyone with irregular bleeding should contact a doctor if they:

  • are trying to get pregnant
  • may be entering menopause
  • have other symptoms, such as painful periods, pelvic pain, or painful sex

Most people’s menstrual cycles vary slightly from month to month. However, significant changes may signal a problem, especially if a cycle is so irregular that a person cannot predict when their period will arrive.

Anyone concerned about irregular cycles should contact a healthcare provider, especially if they want to become pregnant.