Missed period? Here’s how to figure out why

When your regular period does not occur and isn’t just late, it is classified as a missed period. There are many causes for missing a period and these may be temporary or more longstanding. It can be a confusing time trying to work out why this is happening and what you can do.

Of course, the most common cause of a missed period is pregnancy and this is the first thing you and your doctor should rule out. If you aren’t pregnant, there are many alternative reasons for missing a period and for up to 4% of people who menstruate, their period may be absent for greater than three months.¹

The menstrual cycle is regulated by hormones and linked to a variety of other body systems. Broken down to the basics, the brain produces hormones (FSH – follicle stimulating hormone and LH – luteinising hormone) that signal to the ovaries to produce further hormones (oestrogen and progesterone) and together through signalling pathways and feedback they control the menstrual cycle.

Irregular periods naturally occur at the very start of puberty and around the time of menopause while the body is transitioning and hormone levels are balancing. Once this balance has been achieved, the average cisgender woman will have a menstrual cycle of 28 days, although in practice a normal cycle can be anything from 21 days to 40 days.²

Often, the symptoms you have alongside a missed period can indicate what is causing it. Below, we have discussed some of these to help you understand what could be causing your period to be delayed, or to disappear entirely.

Missed periods alongside stress, weight loss, or excessive exercise

As hormones are what regulate your period, things that affect your hormonal balance may cause you to miss a period. These can include stress, extreme weight loss, and over-exercising. This is why irregular menstrual cycles and missed periods occur in athletes and those suffering from eating disorders.

When the body is put under stress and has limited energy resources, a variety of different hormonal changes happen. Ultimately, these are the body’s evolutionary adaptations to protect itself by conserving energy and preventing reproduction during a time that is less “safe” to do so. This can stop menstruation from occurring.

Making lifestyle changes to address the underlying cause can help to normalise your menstrual cycle. For example, if you are under a lot of stress consider making time for relaxation and mindfulness.

Missed period alongside nausea, breast tenderness, and cravings

Missing a period is the most reliable, and often the first, indication of pregnancy. Other symptoms include nausea, breast tenderness, frequent urination and food cravings, however these symptoms will often start weeks after a missed period occurs.³ Therefore, if a missed period is your only symptom then think about ruling out pregnancy.

In the very early stages, a negative pregnancy test does not completely exclude pregnancy. Pregnancy tests detect a hormone called human chorionic gonadotropin (hCG). This hormone increases in amount during the first trimester. Pregnancy tests will only detect this hormone above a certain level (between 20 – 100 mIU/hCG) and therefore in the very early stages of pregnancy, when the level is below this, a pregnancy test will be negative. If you think your missed period is due to pregnancy then wait a few days and repeat the test.

Missed periods alongside changing contraception

Birth control methods can have an impact on your normal periods. When starting or stopping hormonal methods of contraception, periods can become irregular for a time. Long-acting methods of contraception, such as the Mirena coil, can stop periods completely.⁴

After stopping hormonal contraception some will experience loss of periods. This is thought to be due to suppression of the normal hormonal cycle caused by the artificial hormones taken as contraception. Often this resolves within six months, however, if it hasn’t, or you are concerned, then do not hesitate to see your doctor.

Missed period alongside excessive hair growth, acne, or weight gain

Polycystic ovarian syndrome (PCOS) affects up to 26% of people with ovaries, and can cause missed periods alongside the above symptoms.⁵ The cause remains unknown but there is a clear relationship with diabetes. To make a diagnosis of PCOS you must have two out of the following: excess male sex hormone (androgens, including testosterone), irregular or absent periods, and evidence of multiple cysts on one or both ovaries.⁶

PCOS is a condition that is managed through controlling its symptoms. Symptoms are experienced due to high levels of testosterone and insulin resistance. For people who are overweight, losing weight can be crucial in reducing symptoms and preventing long-term complications such as diabetes, high blood pressure, and heart disease. There are medications that can be used to reduce symptoms and to prevent long-term complications, however, medication alone has not been shown to be any better than lifestyle changes.⁷

Missed period alongside weight gain, hair thinning, tiredness

The above symptoms could be indicative of a thyroid condition, specifically an underactive thyroid, and other symptoms include acne and feeling weak. The thyroid gland produces hormones that regulate the body’s metabolism. When this gland becomes underactive it can have an impact on the hormonal system that regulates periods. Thyroid function can be assessed by a single blood test. Treatment to either replace thyroid hormone or block it will often allow periods to resume to normality.⁸

Missed period alongside mood swings, hot flushes, or vaginal dryness

If you are experiencing missed periods alongside any of the above symptoms, you should consider whether menopause could be the cause. The average age for going through the menopause is 51,⁹ and the menopause is defined as a year without periods.

For some, this may occur earlier, and is classified as “premature” if menopause begins under the age of 40. Early or premature menopause may be caused by genetic factors, previous surgery, chemotherapy or radiotherapy to the abdomen or pelvis.

If you are worried about premature menopause then consult your doctor. If this is the reason for your missed periods then it is recommended that your doctor assesses your bone and cardiovascular health as postmenopausal people are at a greater risk of osteoporosis and heart disease.¹⁰

When should you go and see your doctor?

If it is the first time you have missed a period and you have excluded pregnancy then it is most likely your menstrual cycle will return to normal. It is recommended you see your doctor if you have missed three consecutive periods¹¹ or you are having symptoms that could be indicative of an underlying medical problem.

Your doctor will take a full history of your symptoms and it can be useful to keep a record of your menstrual cycle to share with them. They will then examine you, which in most cases will be normal. The first thing they will do is rule out pregnancy by asking you to perform a pregnancy test. Further investigation may include blood tests to evaluate your hormone levels. Depending on the possible causes they will consider further tests and scans such as an ultrasound scan of your uterus and ovaries.¹²

If you are not menstruating it is important to remember that there is still a possibility of becoming pregnant. Therefore, if you do not want to become pregnant your doctor may still recommend that you use birth control.

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Last updated December 2022
Next update due 2025