Almost everyone who menstruates will experience a late period at least once in their lifetimes. Cycles fluctuate, hormones ebb and flow – it’s the way it is. Missed periods, however, are less common.

But, what actually classes as a missed period? And, crucially, what causes them?

PCOS is known to be responsible for around 1 in 3 cases of stopped periods. The question then is – why?

What is considered a missed period?

Let’s talk cycles.

The average menstrual cycle is 28 days long, though, cycles from 21-40 days long are also considered to be normal. Your menstrual cycle begins on the first day of your period, and ends the day before your next period begins.

Periods vary in length from person to person (and from month to month), however, a flow that lasts anywhere from three to seven days is considered regular.

It’s not uncommon for periods to arrive 2-3 days late – cycles fluctuate, it happens. However, if you haven’t come on by day 4 or 5 after your period was due, it’s considered a late period.

So, what is a missed period? There’s no official definition, but some say that missed period is when you go six weeks without bleeding.

What causes a missed period?

According to the NHS, there are numerous reasons why you might miss a period, including:

• Pregnancy

• Stress

• Weight fluctuations (you have gained or lost weight)

• Doing too much exercise, or exercise that’s too intensive

• Using hormonal contraception

• You’re in early menopause

• You have a medical condition, such as diabetes, heart disease, premature menopause, or an overactive thyroid

• You have PCOS

PCOS missed periods: why would PCOS cause your periods to stop?

Hormonal imbalances (high levels of androgens – commonly called “male” hormones, such as testosterone – and high levels of lutenizing hormone (LH)) are found to be present in many people with PCOS, and it’s thought that this could be the reason for irregular or missed periods in people with PCOS.

Androgens and LH are key players in stimulating ovulation – the process which enables a mature follicle to be released by the ovaries ready for fertilisation if it comes into contact with sperm. However, if LH and androgen levels are too high, this can disrupt ovulation. Likewise, raised levels of androgens and LH can impact the menstrual cycle too, resulting in irregular periods or missed periods (though, it’s important to note that not everyone with PCOS experiences irregularity with their cycle).

What should you do if you miss a period?

The NHS recommends talking to your GP if you aren’t pregnant and have missed more than 3 periods consecutively.

If PCOS is determined to be the cause of your missed periods, your GP will help you explore treatment options personal to your circumstances (the contraceptive pill is often prescribed for people with PCOS who are not currently looking to conceive, for example, whilst clomifene, a medicine which helps to stimulate ovulation, is sometimes an option for people with PCOS who want to get pregnant).

In short: don’t suffer in silence – always ask your doctor for help.

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