Irregular Periods & Irregular Cycles

Anyone with a cycle is likely to experience irregular menstruation from time to time. For some of us though, irregular periods and changes to the length of our cycle are more frequent. In this post, we’ll cover what irregular cycles are, how they change over time, some factors that can affect the length of our cycles, plus more menstrual facts.

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What are irregular periods and irregular cycles?

Every cycle starts on the first day of your period. Therefore, shifts in cycle length will cause your periods to arrive either later or earlier than you might expect. So irregular periods are really an effect of irregular cycles.

When we talk about irregular cycles, we’re referring to menstrual cycles that vary in length. There are two ways menstrual cycles can be irregular:

1. They can vary in length between women. So a woman may have a similar length of cycle each month, but this is longer or shorter than the average cycle length (generally considered to be less than 21 days or greater than 35 days).

2. They can vary in length between your own cycles. Irregularity can also be personal, so a woman may experience variation from one cycle to the next (e.g. one cycle is 24 days long and the next is 34 days long). 

Our recent study of over 600,000 cycles found that only 13% of cycles were 28 days long (debunking the myth of the 28-day cycle). Our research also showed that cycles vary substantially between women, and that menstrual cycles get shorter as we get older. While changes in cycle length are perfectly normal, those who do experience these substantial shifts in their own cycle regularity may find it a bit harder to know when they ovulated, or when to expect their next period. 

Why do I get irregular periods?

Irregular cycles are common at the start and end of our fertile years. When we first get our periods they are often irregular until a couple of years after puberty. Periods also become irregular again around menopause until they stop altogether. 

However, even during our fertile years, there are a few things that can trigger irregular cycles and delay our ovulation and/or our periods. Some of these are easier to predict or manage than others, but it’s still useful to be aware of what might be affecting your cycle from one month to the next.

Some causes of irregular cycles:

  • Being unwell/taking certain medication
  • Recent use of hormonal birth control (or emergency contraception)
  • Stress, anxiety or shock
  • Travel
  • Extensive use of alcohol/smoking/drugs
  • Changes to routine
  • Increased activity/sports
  • Low or high BMI
  • Changes to diet
  • Cycle conditions (such as PCOS or endometriosis

Hormonal birth control and irregular periods

Since most hormonal birth control works by stopping ovulation (including the pill or hormonal IUDs) it’s common to not have a period while taking them. You might experience a withdrawal bleed instead, which is a lighter type of bleeding known as spotting. This bleeding can be quite sporadic and, unlike menstruation, it does not signal the start of a new cycle.

It’s worth knowing that once you stop taking hormonal birth control, you might experience irregularities in your cycle for up to a year while your body readjusts. Not all women will experience birth control side effects, but there are a host of hormone-free birth control methods to consider if you are worried about synthetic hormones. 

Trying to get pregnant with irregular periods

To get pregnant you need to have sex on the days in your cycle when you’re fertile. There’s only actually 6 days in any cycle when this is the case - this is called the fertile window. For those with irregular cycles, it can sometimes be harder to predict this fertile window. While there are methods out there to consider when you’re trying to get pregnant, we believe in an approach that is tailored to you - and that’s finding and tracking your ovulation to determine your unique fertile window.

Tracking ovulation and irregular cycles

Ovulation can be a tricky thing to track and predict. Some methods, like the rhythm method, use a calculation that places ovulation day in the middle of a 28-day-cycle, predicting that we are most fertile around day 14. Since most women do not have a 28-day cycle and we all have irregularities in our cycles to some degree, this static ovulation day isn’t going to be very helpful in finding the fertile window.

So what about tracking cervical mucus? This secretion is no secret to those following fertility, but relying on cervical mucus to find the fertile window is a difficult science. Discharge is open to interpretation and varies from woman to woman. Without clinical training, predicting fertility from mucus alone can be extremely difficult.

Another option when it comes to finding the fertile window is the basal body temperature method. The hormone progesterone causes a slight increase in body temperature after ovulation. This can only be measured with a special basal thermometer. However, the rise in BBT is only visible after the fertile window has closed. This is where ovulation prediction comes in. 

Natural Cycles uses an algorithm that learns the pattern of your BBT throughout your cycle and can predict when ovulation will happen and allocate green days (non-fertile) and red days (fertile) based on this prediction. Knowing this fertile window allows the user to either plan or prevent pregnancy depending on her goal.

Those preventing pregnancy with irregular cycles may find they have a greater number of red (fertile) days, this is because the algorithm takes into account the potential shift in ovulation day that can happen with changing cycle lengths. For users planning a pregnancy, red (fertile) days are shown on a scale, showing a brighter red for days when conception is most likely.

Using LH tests (also known as ovulation tests) is a useful way to predict ovulation. These tests detect a surge of luteinizing hormone in urine up to 48 hours before ovulation (they do not confirm ovulation has happened). Those using the Natural Cycles app will get notified at the best time to take an LH test. You can buy LH tests online or find them in your local pharmacy.

We hope you’ve enjoyed learning more about the menstrual cycle. If you’d like to know more about your body, Natural Cycles is a great way to learn the pattern of your unique cycle. Join tens of thousands of women who have already chosen to go hormone-free.

Discover Natural Cycles today

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Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

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Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.