1. You’ve Recently Started Your Periods
If you’ve only recently begun menstruating, you might find that your periods are irregular at first. This unpredictability is perfectly normal in the initial years of menstruation and is not usually a cause for concern. When you start your periods, your body’s hormonal balance is still adjusting, which can lead to inconsistent timing between cycles. Generally, it takes some time for the menstrual cycle to settle into a more predictable rhythm. During this period, your menstrual periods can be irregular, lighter, or heavier than they will eventually become.
2. Pregnancy
If you’ve been sexually active within the last month and your period is late, you’re going to worry. Pregnancy is the most common cause of a late or missed period. Early pregnancy symptoms such as cramps, bloating, nausea, fatigue, breast tenderness and spotting when you wipe (or in your underwear), are very similar to the symptoms you get towards the end of your cycle. This makes it difficult to tell if your cycle is off by a few days, or if it’s a sign of pregnancy.
If your period is a week late and you’ve had sex within the last few weeks, the most sensible course of action is to do a pregnancy test. Even if you’re using contraception, you can’t rule out pregnancy altogether, as no contraception is 100 per cent effective.
Most pregnancy tests can be taken from the first day of a late or missed period. If you’re not sure of the exact date your next period is due, the NHS recommends doing a pregnancy test at least 21 days after your last had unprotected sex.
Pregnancy tests are widely available in pharmacies and supermarkets. You can get one for free from your GP surgery, sexual health clinic, or a Brooks Centre if you’re under 25.
3. Stress
Stress can be one of the main reasons to miss a period. As stress levels rise, a woman’s reproductive system and hormone balance can be affected. Research shows that for some women, stress can play a role in causing your period to be delayed.
When stress levels reduce, your menstrual cycle will usually return to its normal pattern, without any long-lasting effects. Try not to worry about a late period that may be caused by stress. If you are feeling stressed, take time to relax, exercise, or try breathing exercises. You should contact your doctor for support, if your stress is overwhelming or hard-to-manage.
4. Hormones
Hormone imbalances involving prolactin or thyroid hormones, can cause a woman’s period to be late. These imbalances can be easily identified with a blood test.
If you have a hormonal imbalance, your doctor will investigate the reasons for it. Certain medications can help your periods return to their normal cycle.
5. Higher Body Weight
Being overweight or suddenly putting on a significant amount of weight, can affect your menstrual cycle by causing excess oestrogen production. This can lead to a late or missed period.
If you think that your weight is causing period irregularities, you should speak to your doctor. Obesity and missed periods can sometimes indicate a health condition, such as polycystic ovary syndrome (PCOS), so it is important to get it checked out. Alternatively, your doctor will be able to provide you with healthcare advice and signpost you to services which can support you to lose weight. Weight loss medication is also an option where lifestyle measures have failed.
6. Being Underweight
On the flipside, significant weight loss and low body weight can cause a woman to miss her period. Being underweight or having too little body fat compared to your body mass, known as a low body-fat ratio, can reduce your oestrogen reproductive hormone levels so that ovulation and menstruation do not occur.
You should see your doctor or a dietician if you have excessive weight changes or you are underweight. They can help you to get the right amounts of nutrients your body needs to function correctly and resume your menstrual cycle.
7. You Have a Thyroid Condition
Thyroid problems can cause abnormal menstrual changes. Your thyroid is a gland responsible for your body’s metabolism.
If you have an overactive thyroid, known as hyperthyroidism, your periods can become lighter, less frequent or absent. Additional symptoms of hyperthyroidism include weight loss, rapid heartbeat, increased sweating and trouble sleeping.
If you have an under active thyroid, also known as hypothyroidism, your periods may be less frequent, but heavier. Other symptoms of hypothyroidism include weight gain, fatigue, dry skin and hair loss.
A blood test can help your doctor determine if you have a thyroid problem. Medication is available to help you
8. Perimenopause
Menopause usually occurs in women between the ages of 45 and 55. It is officially recognised when a woman hasn’t had a period for at least 12 months. After menopause, you won’t have a period again.
Perimenopause, also known as the menopause transition, begins several years before menopause. It is a time when your body starts transitioning to menopause. During this time, your ovaries gradually begin to produce less oestrogen. This can cause changes in your menstrual cycle. Your periods may come more or less frequently, be shorter or longer, or be lighter or heavier.
Other symptoms of perimenopause include mood swings, hot flushes and night sweats, brain fog, sleeping difficulties, vaginal dryness, and vaginal burning.
The average age for perimenopause is between 40-45. However, some women go through it as early as their 30’s.
You should call your doctor if you have symptoms that are concerning, or you haven’t had a period for 3 months (especially if you are under 45 years). They can do a blood test to check your hormone levels and help pinpoint the cause.
9. Birth Control – The Contraceptive Pill
If you have recently started, changed, or stopped taking hormonal contraception, there’s a good chance your periods will be affected. Your body needs to adapt to the changes in hormone levels caused by taking the contraceptive pill. This may result in your period being less frequent or lighter. Some women stop bleeding altogether when taking the pill.
The contraceptive pill and many other hormonal birth control options work by preventing ovulation. They do this by altering the levels of natural hormones your body makes. Many also thin the lining of your womb to a point where a period is not necessary. Usually, this isn’t harmful, but you should speak to a doctor with any concerns about your birth control method.
You should also bear in mind that no contraceptive pill offers 100% pregnancy prevention. So, if your period is late, you may wish to take a test.
10. Polycystic Ovary Syndrome (PCOS)
Polycystic ovarian syndrome (PCOS) is a common medical condition affecting hormone levels. It can result in persistently late or irregular periods, and in some women, it can stop periods altogether.
PCOS is caused by a hormonal imbalance in women. Polycystic ovaries have many underdeveloped sacs in which eggs develop. Often these sacs are unable to release an egg, resulting in no ovulation.
If you have PCOS you may experience other symptoms as well as changes to your periods. These include excessive hair growth or thinning hair, weight gain, acne and difficulty becoming pregnant because of irregular or missed periods. Some women do not experience any symptoms.
You should book an appointment with a healthcare professional if you think you have PCOS symptoms. They may be able to offer treatment to relieve them. Often lifestyle modifications such as healthy eating and weight loss are recommended.
11. Changes in Diet
Changes in your diet can cause your period to be late or irregular. Research shows that hormone production can be affected by diet, which can affect your menstrual cycle.
If you limit your calorie intake and range of foods, you may prevent your body from getting enough nutrients to meet your hormonal needs. Depending on the extent of your diet, it is possible for your body to enter starvation mode and use the nutrients for other vital areas, such as your brain and heart health. This can result in missed, irregular or late periods. Women with eating disorders such as anorexia nervosa and bulimia, often have irregular or missed periods.
A diet lacking minerals and vitamins such as iron, calcium, magnesium and zinc, folate, or vitamins B, C and D, are associated with menstrual cycle changes.
12. Exercise
Excessive exercise and intense physical activity can affect your cycle. This is common amongst women training for intense sporting events such as marathons. In fact, many professional athletes experience irregular period patterns.
Moderate exercise, such as going to the gym, swimming, or cycling a few times a week, is very important for your general health and will not usually impact periods. But putting your body under intense physical stress may affect your adrenal, thyroid and pituitary glands, causing a hormonal imbalance. This, in turn, impacts ovulation and can change your menstrual cycle, resulting in late, lighter or missed periods.
If you are planning on undertaking a strenuous exercise regime, optimising your diet with nutritious and energy-boosting foods will help to support a healthy period cycle. If your periods have become irregular or stopped altogether due to a significant increase in exercise, you should talk to your doctor.
13. Breastfeeding
If you’re breastfeeding, your periods may be irregular or absent. They might not return at all until you stop breastfeeding. This is because the hormones responsible for milk production also suppress ovulation.
You should be aware that you are still fertile whilst breastfeeding, even if you are not getting periods. Many women think they cannot fall pregnant whilst breastfeeding. This is not true. You need to use contraception if you do not wish to fall pregnant.
14. Travelling or Disrupting your Sleep Cycle
If you’re jet-lagged from travelling, a shift worker changing schedule, or you suffer from disrupted sleep patterns, you may find that your period turns up earlier or later than expected.
Your menstrual cycle is closely associated with your circadian rhythm. Circadian rhythms are 24-hour cycles that are part of the body’s internal clock. They help to regulate your hormone production and can affect ovulation and your periods as a consequence.
The good news is that once you settle into a new regular wake-sleep pattern, your hormone levels should readjust, and your period should return to normal.
15. Long-Term Medical Conditions
There are some long-term medical conditions that can also cause late or irregular periods. Women with diabetes may have an increased risk of experiencing unpredictable menstrual cycles. Remember, these are long term conditions and so period changes happen gradually over a long period of time, as opposed to a one off.
If you have ongoing period changes you should see your doctor.
It’s not only long-term illness that can throw your period out of sync. The added physical toll that an acute short-term illness has on your body, can delay your period. This is because your body prioritises its resources to help you get better.
16. Covid-19 Vaccine
Over 30,000 women have reported to the MHRA Yellow Card scheme that they have had changes to their menstrual cycle after having the COVID-19 vaccine. Changes include frequency, duration, regularity and volume of menstruation. It is very difficult to know if these changes are a direct result of the vaccine itself, or due to the wider effects of the pandemic. In this BMJ article, it states that most of these changes are temporary and periods return to normal after a single cycle.
