Irregular periods: What causes them, and how to get yours back on track

The average menstrual cycle is 28 days long, although a regular cycle is anywhere from 21 to 38 days. Sometimes, your cycle may be shorter or longer than usual. An occasional irregular period isn't usually a cause for concern. But consistently irregular periods may be caused by certain health issues like thyroid problems or polycystic ovary syndrome (PCOS). If you do have irregular periods, your provider can help you figure out what's going on.

Calendar for period tracking
Photo credit: Thinkstock © iStock

Having an irregular period means that the length of time between the first day of your period and the first day of the next changes from cycle to cycle. It might come a few days earlier than expected or a few days late. A period that rarely arrives on schedule can throw you for a loop, especially if you're trying to get pregnant.

Most of the time the menstrual cycle follows a pretty set schedule. Every month at roughly the same time, the ovaries release an egg. That's called ovulation. If that egg isn't fertilized, your hormones signal your body to shed the tissues lining your uterus and you get your period. You bleed for around five days, and then the whole cycle starts over again.

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It's like clockwork. Well, not always.

The average menstrual cycle is 28 days long, but it can range from 21 to 38 days. Some women have more unpredictable cycles that change in length from month to month. Not only does having an irregular period make it hard to know when it's time to pick up a new box of tampons or pads, but it can make it more difficult to know when you could get pregnant.

If you're wondering, "Why is my period irregular?" there are a few possible reasons.

What causes an irregular period?

Abnormal periods are the norm during the teen years when your body is still establishing its menstrual rhythm. It's also common in your 40s and 50s as you inch closer to menopause.

If you're not in either one of these age ranges here are some other reasons you may have irregular periods:

  • Stress. You may notice that your periods get out of whack whenever you're under a lot of stress. That's because the stress hormone, cortisol, affects the release of estrogen and progesterone, which control your menstrual cycle.
  • Birth control pills. Taking the "Pill" will make your menstrual cycle more regular while you're on it. Once you go off birth control you can expect a little irregularity for a few months as your cycle gradually eases back into its previous rhythm.
  • Weight loss or gain. Quick or dramatic weight swings – up or down – can throw off your menstrual cycles. Irregular or missed periods are one sign of eating disorders like anorexia nervosa or bulimia. Hormonal changes that go along with weight gain or loss may be behind these menstrual changes.
  • Problems with your ovaries. Polycystic ovary syndrome (PCOS) causes your ovaries to make too much of male hormones called androgens. This prevents your eggs from maturing, which leads to irregular periods. About 1 in 10 women with irregular periods have PCOS. In premature ovarian failure (POF) (also called primary ovarian insufficiency, or POI), your ovaries stop working before age 40 – years before you would typically start menopause. You ovulate less and less often over a few months or years before your periods stop altogether.
  • Pelvic inflammatory disease (PID). Painful or irregular periods can be a sign of PID, a bacterial infection of the reproductive organs.
  • Hormone disorders. Irregular periods could be a sign that your hormones are out of balance. An overactive (hyperthyroidism) or underactive (hypothyroidism) thyroid gland and excess prolactin (hyperprolactinemia) can throw off your menstrual cycle.
  • Endometriosis. When tissue that forms the lining of your uterus (endometrium) forms outside of the uterus, such as in the ovaries or fallopian tubes, you may have longer periods or shorter intervals between periods.

How to calculate ovulation with irregular periods

Using an ovulation calculator to figure out your most fertile days can help you predict when you'll have the best odds of conceiving. But what if you have irregular periods and you ovulate at different times in each cycle? An ovulation calculator that works for irregular periods doesn't really exist.

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Instead, you may need to rely on other fertility tracking methods. One technique to try is measuring your basal body temperature (BBT). Your body temperature will rise slightly when you ovulate, giving you a window into the best time to have sex.

Or you can buy ovulation test strips. Using a bit of your urine or saliva, these strips can alert you to when ovulation is imminent.

Signs of pregnancy when you have irregular periods

A missed period is one of the most common ways that women know they're pregnant. Once you conceive, your body releases hormones that basically shut down ovulation. But what if your period comes sporadically? One missed period can bring excitement – or panic – when you're not actually pregnant.

Watch for these other signs of pregnancy when you have irregular periods:

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Keep in mind that many of these symptoms happen for other reasons. You might feel extra tired if you haven't been sleeping well or you have an infection, for example. The only way to know for sure is to take a pregnancy test.

What to do about irregular periods

Your periods might snap back into a normal rhythm eventually if the cause was something temporary, like work-related stress. In other cases, the way to treat irregular periods depends on their cause.

Taking hormonal forms of birth control like combination birth control pills or progestin-only pills can help to regulate your cycle, if you're not planning a pregnancy. These are also treatments for PCOS.

Treating whatever other problem that caused your menstrual cycle to become irregular can also do the trick. For example, if you have an eating disorder, you may need counseling and nutritional therapy. For PID, antibiotics help you get rid of bacteria that caused the infection.

If you're having irregular cycles, talk with your provider. It's a good idea to track your cycle using an app or calendar so they can get a good idea of exactly what's going on when you meet. They'll suggest treatment options for any underlying health issues, which will in turn help regulate your cycles

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Stephanie Watson
Stephanie Watson is a freelance health and lifestyle writer based in Rhode Island. When she’s not busy writing, Watson loves to travel, try new cuisines, and attend as many concerts, shows, and plays as she can fit into her busy schedule.