Perimenopause is the period of time leading up to the menopause when women may begin to experience irregular periods and other symptoms. The perimenopause may start months or years before periods actually stop.

Menopause is a point in time 12 months after a woman's last period. For most women this occurs between the ages of 45 and 55 years but it can happen earlier.

Early menopause is defined as menopause (i.e. no periods for one year) that happens between ages 40 and 45. About 1-in-20 women will naturally go through early menopause. There are some factors that make early menopause more likely:

• family history: e.g. if your mother had early menopause you are more likely
• smoking
• some autoimmune conditions

It's best to take your blood samples in the morning, before you've eaten any food. Avoid any biotin supplements for two days before this taking this test. If biotin is prescribed by your doctor then you should discuss with them before stopping it.

On average, menopause symptoms last for about 4 years from your last period. Symptoms will often change over time and some women can continue to experience symptoms for 10 to 14 years.

For most women the perimenopause begins between ages 45 and 55.

Although the perimenopause and menopause can cause many symptoms, some of its most important effects are those that you cannot see or feel. The hormonal changes during this stage in life significantly affect your metabolic health - your cholesterol levels and sugar-handling for example. These have a big impact on your risk of heart disease, stroke, dementia and even cancer. Bone density also falls during this period putting you at higher risk of fractures. Our Perimenopause and Menopause Blood Test is largely designed to give you insights into these factors so you can optimise your health and reduce your risk.

We also test your thyroid function because thyroid conditions become more common as women age and can cause very similar symptoms to those of the perimenopause. Lastly we can optionally check your hormone levels which can give you an indication of whether you're likely to be perimenopausal. You may not require these if your symptoms are typical and you're between 45 and 55 but they can be useful if there's any doubt.

Testing levels of LH, FSH and oestradiol can give an indication of the perimenopause or menopause but you do not need a blood test to tell if you are perimenopausal or menopausal. You can usually tell if you're perimenopausal based on your age (typically between 45 and 55) and the symptoms you're experiencing. Similarly, the menopause is defined as the time one year after your last period.

However, blood tests for hormones can still be useful for a number of reasons. Firstly, sometimes perimenopause symptoms can be confused with other conditions. For example, thyroid disease is very common as women get older and can cause many of the same symptoms as the perimenopause. Secondly, blood tests can be useful to indicate that the perimenopause is likely if you're unsure of the cause of symptoms. This can sometimes be the case if you're younger than is typical for the perimenopause - e.g. under 45.