Menstrual cycle: how much do you know?

The length of a menstrual cycle is different for every woman. A period every 28 days is often described as typical, but a cycle anywhere from 21 to 40 days can be perfectly normal too. Understanding your own menstrual cycle helps you notice when something changes, and know when it is worth asking for advice.

What counts as a menstrual cycle?

Your menstrual cycle runs from the first day of your period to the day before your next one begins. Over a lifetime, the average woman will have around 480 periods. Hormones from the ovaries control each cycle, preparing the womb for a possible pregnancy and then shedding its lining if pregnancy does not happen.

What is a period?

A period is made up of blood and the lining of the womb. It usually lasts between 2 and 7 days, and for most women it lasts around 5. During that time, most women lose about 3 to 5 tablespoons of blood. It can feel like more, especially on heavier days, but this is the usual range.

What is ovulation?

Ovulation is when one of your ovaries releases an egg. Once it has left the ovary, the egg lives for up to 24 hours. If sperm meets the egg during that time, it can be fertilised. Ovulation usually happens around the middle of the menstrual cycle, although the exact timing varies from woman to woman and from month to month.

Menstrual cycle changes to look out for

Some changes in your menstrual cycle are worth discussing with a doctor:

• periods that come less than 21 days or more than 35 days apart
• missing three or more periods in a row
• a flow that is much heavier or lighter than usual for you
• periods that last longer than seven days
• periods with significant pain, cramping, nausea or vomiting
• bleeding or spotting between periods, after sex or after the menopause

Bleeding after the menopause should always be checked promptly, even if it is only light.

What can cause an irregular menstrual cycle?

There are many possible reasons why a menstrual cycle may change. Common causes include:

• stress and lifestyle factors, such as weight change or intense exercise
• hormonal contraception, including the pill
• endometriosis
• polycystic ovary syndrome
• pelvic inflammatory disease
• polyps in the womb, or fibroids

Most of these causes are treatable. Often, a conversation, an examination and an ultrasound scan are enough to find out what is going on.

Tracking your menstrual cycle

A period tracker app or a simple diary can tell you a great deal. Note the first day of each period, how many days it lasts, how heavy it feels and any pain or other symptoms. After three or four months, you will have a clear picture of what is normal for you. That makes any change much easier to spot and to describe to your doctor, and it also helps if you are planning a pregnancy.

When to seek advice

If you have concerns about your menstrual cycle, or think something is not right, it is worth speaking to a gynaecologist. Keeping a simple diary of your periods, their length and how heavy they are makes that conversation much easier. Our menstrual disorders page explains how heavy, painful and irregular periods are investigated and treated.

The Royal College of Obstetricians and Gynaecologists has helpful patient information on periods and gynaecological health, and NICE guidance explains how heavy menstrual bleeding is assessed and managed.

To arrange an appointment with Mr Jafaru Abu at The Park Hospital, Nottingham, get in touch with the team and they will be happy to help.