5 Things You Need to Know About Irregular Periods

McKenna Princing Fact Checked
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You thought you had it all figured out, but then everything changes. We’re talking about your period, of course, which has a knack for lulling you into a false sense of predictability and then suddenly flipping the script. 

Thought your period came at the end of the month? Now it’s at the beginning. Not to mention the entire month your period skipped.

It turns out irregular periods are pretty common — even for people on birth control. Here’s what you need to know about what’s normal and what’s not.

Irregular is different for everyone

“The most important thing for patients to understand is your period and your regularity is different from other people’s,” says Dr. Ying Zhang, a family medicine doctor who sees patients at the UW Neighborhood Northgate Clinic and the Family Medicine Clinic at Harborview Medical Center. 

Maybe you’ve heard that a ‘normal’ cycle is between 28 and 30 days. Or that your period should last four or five days max. 

This may be true for some people, but in reality periods can vary a lot more and still be considered normal. 

Cycles that last as few as 21 days or as long as 40 days are possible, Zhang says. 

In terms of length, a normal period usually lasts between two and seven days. 

So if you occasionally skip a period or your period comes late some months, there’s probably nothing to be worried about. Still, if you’re thrown off by your period’s irregularity and want to get a better sense for any patterns … well, there’s an app for that.

“A lot of people use period tracking apps, which is helpful to understand what is happening with their cycle and the duration,” Zhang says.

Many things can cause irregular periods

You know that stress you’ve been feeling about your new job or moving into a new house? It can wreak havoc on the regularity of your cycle.

During times of your life that are more stressful, your period could be more irregular, Zhang says. This could mean it comes later or even skips a month. 

Other things that can cause irregular periods include weight gain or loss; medical conditions like a thyroid disorder or ovulatory dysfunction; high levels of testosterone, such as what happens to women who have polycystic ovary syndrome; or putting a lot of stress on your body due to a strict exercise regime, which sometimes happens to female athletes.

And, for those who are wondering, infertility can cause irregular periods — but not the other way around, Zhang says. If you’re experiencing fertility issues and aren’t menstruating regularly, there’s probably an underlying medical issue that you need to address, so make sure to talk with your doctor.

Your period can change over time

Maybe you used to get a heavy flow during your periods, but now they’re lighter. Or maybe some periods are lighter and others are a little heavier. This is pretty normal, Zhang says. 

“It depends on what’s going on with the lining in your uterus,” she says.

The time between each cycle can also vary: Maybe one month it’s 28 days, then the next it’s 30 days. 

Your PMS symptoms (or lack thereof) can vary each cycle, too, depending on hormone fluctuations, Zhang says. 

It’s not uncommon for your period to become shorter as you get older, too. In adolescence, periods tend to be longer and a little heavier, then ease up after a few years. Menstruation changes in the years before menopause and can be more irregular after pregnancy.

Birth control can make your period irregular — at first 

Hormonal contraceptives like birth control pills and the hormonal intrauterine device (IUD) work to prevent pregnancy by interfering with the natural fluctuation of hormones in your cycle that form eggs and ovarian follicles. This interference is what prevents you from getting pregnant.

Some hormonal contraceptives, like the hormonal IUD, also prevent pregnancy by thinning the lining of your uterus, known as the endometrium, so an egg can’t attach to it.

A thin endometrium means your body doesn’t need to shed it as often or at all, so your period may become much lighter or stop altogether, Zhang says. 

Spotting or bleeding between periods can happen when you start using a new method of hormonal birth control, Zhang says. Plus, some people choose to use birth control in a way that suppresses their period entirely, like taking birth control pills continuously (and skipping the placebo pills), which can also result in spotting until your body gets used to the new routine.

But if you have spotting or bleeding between periods that doesn’t go away within a few months, or if there’s a sudden change in your cycle, that’s worth noting, Zhang says. 

“If you’re on an IUD and you don’t get your period, if all of a sudden you have heavy bleeding or have irregular bleeding, that is something to ask your doctor about,” she says.

Some symptoms are more concerning than others

While a skipped period isn’t automatically cause for concern, a few other things can be. 

If you suddenly start getting a heavy flow during periods or start bleeding between periods (and you haven’t recently started a new type of hormonal birth control), that’s something you’ll want to bring up to your doctor, Zhang says. 

Likewise, if your cycle lasts less than 21 days or more than 40, it’s also worth a visit to your primary care provider. If you skip more than three periods in a row and aren’t pregnant, that’s also something you’ll want to get checked out. 

Getting severe cramps during your period, when you previously didn’t, could also be cause for concern. 

The bottom line: If you think something’s up, even if it’s supposedly normal, just get it checked out. For example, Zhang sees many patients who come in because of a skipped period, which is something they’re concerned about but that isn’t necessarily a red flag to a doctor.  

“If you’re having new symptoms that are concerning to you, it’s always fine to go talk with your doctor about it,” Zhang says.