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Why is my period late? 7 potential reasons

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From pregnancy to contraceptives to stress, a late period can have different causes. We ask Dr Elisabeth Rosén, a Livi medical doctor who specialises in gynaecology, for the possible reasons – and when to speak to a doctor

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When your period doesn’t show up on time, it can be worrying – especially if you usually have a regular menstrual cycle.

So, what constitutes a late period? ‘Your period is typically considered late if it’s more than 5 days past when it was due,’ says Dr Elisabeth Rosén.

‘Tracking your cycle is a good way to get more familiar with what’s going on with your body. It’s much easier to identify a late period – or when something else is going on – when you’re already aware of what’s normal for you.’

What’s considered a normal cycle?

For most people, the average menstrual cycle is 28 days – but a healthy cycle can last anywhere between 21 and 45 days.

While some people get their periods right on schedule, irregular periods are fairly common. Sometimes your periods may stop altogether. An absent cycle is also known as amenorrhea, and if this happens for you, it’s best to speak to a doctor.

Why is my period late?

Here are some potential reasons why your period might be later. When in doubt, speak to a doctor.

1. You’re pregnant

If you’re sexually active, pregnancy could be causing a late period.

‘The main purpose of the menstrual cycle is to prepare your body for pregnancy each month,’ explains Dr Rosén. ‘With each cycle, the lining of your uterus thickens to create the ideal environment for a possible pregnancy. If an egg isn’t fertilised, the lining of your uterus breaks down and begins to shed – which is also known as your period.

‘When you fall pregnant, a fertilised egg implants into the uterine lining and there’s no need for a period.’

It’s important to note that your cycle may be late for a variety of factors, and it doesn’t necessarily mean you’re pregnant. This can be disappointing to discover if you’re trying to conceive or a relief if you’re not trying for a baby.

Either way, it’s a good idea to take a home pregnancy test to rule it out. Pregnancy tests can generally determine whether you’re pregnant on the first day of a late period.

2. You’re taking contraceptives

If you’ve just started or stopped taking hormonal birth control, it may affect your period and cause delays. Some types like the intrauterine system (IUS), progestogen-only pill and contraceptive injection may cause your periods to stop altogether.

‘Both the combined and progesterone-only pills can affect your cycle by suppressing the production of your hormones,’ says Dr Rosén. ‘The combined oral contraceptive pill contains artificial versions of the hormones oestrogen and progesterone. These hormones hinder your ovaries from releasing eggs and can affect how frequent your periods are,’ she says.

The progesterone-only pill can also cause periods to stop or become more frequent, lighter or irregular.

3. You’re transitioning into menopause

There are certain times when it’s normal for your period to be irregular – when you first start menstruating and when the menopause transition starts.

‘It’s common for your periods to become irregular in the years leading up to menopause,’ says Dr Rosén. ‘Your body’s production of oestrogen and progesterone fluctuates during perimenopause and this affects ovulation and the lining of the uterus, leading to irregular periods.’

Menopause usually happens between the ages of 45 and 55. But premature menopause can happen to younger women too. If you have symptoms of perimenopause, speak to a doctor.

4. You’re extremely stressed out

If you’re going through a stressful time in your life, possibly due to a relationship break-up or demands at work, it can have a major impact on your menstrual cycle. One study found that women who were experiencing high stress levels were more likely to have irregular cycles.

‘Stress takes a toll on your body,’ explains Dr Rosén. ‘It releases high levels of the stress hormone cortisol, which affects your production of oestrogen and progesterone – hormones vital for a cycle. Limited amounts of these hormones may cause a period that’s irregular or even delayed.’

If you think stress may be affecting your periods, and lifestyle factors like prioritising sleep and relaxation techniques aren’t helping, speak to a doctor.

5. You’re over-exercising

There’s no denying that exercise is good for your health. But if you exercise too much (in certain cases known as orthorexia), the reproductive hormones responsible for your periods may be disrupted in a similar way to when you’re stressed. Researchers found that 57% of ballroom dancers missed periods due to their rigorous training.

6. You’ve gained or lost a significant amount of weight

Changes in body weight are another common reason for a late period. ‘Being underweight and restricting the number of calories you eat decreases the production of hormones required for ovulation,’ says Dr Rosén. ‘Losing too much weight, as with severe stress and excessive exercising, can affect the body’s reproductive hormones, which control your menstrual cycle.

‘Similarly, if you put on a lot of excess weight, your body may produce an excess amount of oestrogen, which can result in a cycle that’s delayed – or that stops.’

7. You have a chronic illness

Irregular or delayed periods may also be a sign that something more serious is going on. Both polycystic ovary syndrome (PCOS) and thyroid problems can affect your menstrual cycle.

PCOS is an endocrine disorder, which affects as many as 1 in 10 women in the UK and is responsible for as many as 1 in 3 instances of stopped periods.

‘PCOS causes a hormone imbalance where your body produces higher-than-normal amounts of testosterone,’ says Dr Rosén. ‘This affects the menstrual cycle, and ovulation may either happen irregularly or not at all.

‘Your thyroid hormones play an important role in your body, including regulating the menstrual cycle. When an underactive thyroid doesn’t produce enough hormones, it can cause irregular periods.’

When should I see a doctor for delays in my period?

‘Everyone experiences periods differently, but if you’re experiencing delays in your period for more than 2-3 months with no obvious explanation, you should speak to a doctor,’ advises Dr Rosén.

Make an appointment with a doctor if:

  • You miss 3 or more periods
  • You have irregular periods that change in length and heaviness from one month to the next
  • Your periods are suddenly irregular and you’re under 45 years old
  • You experience bleeding or spotting after menopause or in between periods
  • Your period lasts more than 7 days
  • Your periods are more often than 21 days or less often than 35 days apart

This article has been medically reviewed by Dr Elisabeth Rosén, a Livi medical doctor who specialises in gynaecology.

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