Some people get their periods like clockwork. Others… not so much. If it feels like Aunt Flo’s arrival date is always a mystery for you, you probably have an irregular menstrual cycle.

Irregular periods have a bunch of possible causes, from stress to medical issues. Here’s what you need to know about irregular periods and pregnancy.

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Yaroslav Danylchenko/Stocksy United

The average menstrual cycle is 28 days long, but everyone is different. Any cycle between 21 and 45 days with a period that lasts 2 to 7 days is considered normal.

But if your flow is like your weird roommate who shows up at random times and you never know how long they’re going to stay, your periods would be considered irregular.

A few different things could be going on. Here’s how to figure out what’s up.

1. You’re dealing with a medical condition

Several medical issues could be affecting your cycle:

  • Thyroid disorder. This is a pretty common culprit. A 2016 study in 100 women found that 44 percent of those who had period irregularities also had thyroid disorders. Hypothyroidism (an underactive thyroid) may cause longer, heavier periods, while hyperthyroidism (an overactive thyroid) may cause shorter, lighter ones.
  • Polycystic ovary syndrome (PCOS). In the United States, 6 to 12 percent of people who menstruate have PCOS. It affects your ovaries and your hormones, so it can cause irregular periods and other symptoms. You may notice elevated testosterone levels, ovarian cysts, weight gain, acne, or hair loss.
  • Uterine fibroids. These are noncancerous muscular tumors inside your uterus. These growths can affect your period, but they can also cause fertility issues, lower back pain, bloating, pain during sex, and a swollen abdomen.
  • Endometriosis. This painful condition causes tissue similar to your uterine lining to grow outside your uterus. It affects about 10 percent of people who menstruate. It can cause long, heavy periods with spotting in between.
  • Some cancers. Cervical, uterine, and endometrial cancers can all cause super long and heavy periods, bleeding between periods, and other symptoms.

Other underlying conditions, like Cushing syndrome, pelvic inflammatory disease, and uncontrolled diabetes, could also cause irregular periods.

2. You’re nursing your little one

Prolactin (think: pro-lactation) is the hormone that helps you produce milk to feed your newborn. It can also suppress the other hormones that bring on your flow.

When you’re breastfeeding, you may stop getting periods altogether or get super light ones. Things will go back to normal as soon as your tiny human weans.

3. You’re nearing “the change”

If you’re around 40 years old, you could be in perimenopause. This is the phase before you reach menopause, and it brings all kinds of hormonal fluctuations, which can also mean shorter, lighter periods.

Along with a flaky flow, you’ll probably experience other symptoms, including:

4. Something else is up

Here are some other factors that might lead to irregular periods:

  • Weight. Research suggests that being either overweight or underweight can affect your cycle.
  • Exercise. If you exercise a lot, your reproductive hormones can dip so low that your periods become irregular or stop altogether.
  • Stress. Stress can wreak havoc on your body, including your hormones.
  • Smoking. A 2018 study found that smoking was significantly associated with irregular periods, especially in people who started smoking before age 19.
  • Medications. Blood thinners, hormone replacement meds, antidepressants, epilepsy meds, chemo drugs, and excessive ibuprofen are just a few of the medications that could be affecting your cycle.

For many people, it’s totally possible to get pregnant with irregular periods, but it might be a bit harder.

Irregular periods make it difficult to estimate when you’re going to ovulate (aka your fertility window). And if you don’t know when you’re ovulating, it’s harder to know the ideal time to have baby-making sex.

The cause of your random cycle could also impact your chances of getting pregnant. For example, PCOS, endometriosis, and uterine fibroids can affect fertility. Sometimes irregular periods are a sign that ovulation has stopped.

While it’s still best to get checked out by a doctor to address any serious conditions that might be causing your irregular periods, there are some things you can do to increase your odds of getting pregnant on your own.

1. Use an ovulation predictor kit

These kits are available over the counter at most stores, and they’re pretty accurate at detecting a surge in luteinizing hormone (the one that triggers ovulation). Ovulation predictor kits are easy to use — you pee on them just like a pregnancy test.

But be warned: They’re a lot pricier than pregnancy tests. That cost can start to add up if you need to use a lot of them thanks to an irregular cycle.

2. Look for an increase in cervical mucus

When you’re nearing ovulation, your cervical discharge will prob look like clear, raw egg whites. You can usually even stretch it between your fingers.

Here are three ways to check your cervical discharge:

  1. Before you pee, wipe the opening of your vagina with white toilet paper and observe the color and feel of the mucus.
  2. Look at the color and texture of discharge in your underwear.
  3. Put clean fingers into your vagina, and then check the color and texture by rubbing the mucus between your thumb and index finger.

3. Monitor your basal body temp

Your basal body temperature is your bod’s temp when you’re completely at rest.

That means you’ll have to check it first thing in the morning. (Make sure you check it before you do literally anything else, including getting up.) You’ll need to track your temperature every day, all month long.

There will be a slight decrease right before you ovulate, followed by a slight increase — about half a degree or so — when you ovulate.

4. Have *a lot* of sex

If you’re not sure what the best time is to have baby-making sex because you’re not sure when you’re ovulating, you can try having sex all the time. Looking for a way to mix it up? You can add sex toys or some role play if your partner’s game.

Need to get a little more in the mood a little more often? Some foods, including dark chocolate and salmon, may jump-start your sex drive.

If your period never comes on time, it’ll be difficult to tell when you’re “late.” If you’ve had sex without a barrier or another birth control method, you can take a pregnancy test:

  • 36 days after your last period
  • 28 days after having sex

In either case, if you’re pregnant, your level of human chorionic gonadotropin (aka the pregnancy hormone) should be high enough at that point for the test to detect.

You can take a test sooner (around 14 days after sex), but a negative result won’t be as reliable. You’ll want to take another test in another 2 weeks if you still haven’t gotten your period. False positives are rare, though, so if you test positive at any point, you’re most likely pregnant.

Irregular periods have several possible causes. It’s important to find out what’s throwing off your flow because some medical conditions can make it more difficult to get pregnant, especially if they remain untreated.

But irregular periods don’t mean it’s impossible for you to conceive. If you’re ovulating, there are ways to increase your chances of pregnancy. Talk with your doctor to find out why you’re experiencing irregular periods. They can help you treat any underlying issues.