Dr Laura Cassidy, an obstetrician and gynaecologist, explains what's normal and what's not for your monthly period.
Periods last around three to seven days. The average menstrual cycle lasts 28 days, although it's normal to have a cycle that's shorter or longer than this.
Women's periods can change. This doesn't necessarily mean there's a serious problem, but it does need to be checked.
"To get help, women should go where they feel most comfortable," says Dr Cassidy. "This could be a well woman clinic, a general practice or a community contraceptive clinic."
Missing a period could mean that you're pregnant. If you miss a period and you've had sex, take a pregnancy test to find out if you're pregnant.
"If you're not pregnant and you miss two or three periods, get medical advice," says Dr Cassidy. For many women, missed periods are due to upset hormones, and you may need help.
There can be other reasons for missed periods in some women, including:
- sudden weight loss
- intense athletic activity
- taking the contraceptive pill
"If you've been on the contraceptive pill for a long time, you might miss a period every now and again. It's not particularly significant," says Dr Cassidy. Some types of contraception, such as the injection and the IUS (intrauterine system), can stop periods altogether.
It's not unusual for women approaching the menopause to miss periods, as ovulation becomes less regular. The average age for the menopause is 50 to 55, but sometimes women can have an early menopause in their teens, 20s or 30s (see Early menopause - real story).
Women whose periods stop before they're 45 or who are still bleeding when they're over 55 years old should get medical help.
Bleeding between periods or after sex
Bleeding between periods or after sex must be checked by a professional as it can be a sign of infection, abnormalities of the cervix or, in rare cases, cancer.
"If you've got inter-menstrual bleeding (between periods) or post-coital bleeding (after sex), there might be some abnormality of the cervix," says Dr Cassidy. The abnormalities can be harmless, for example polyps, or they can be due to an infection such as chlamydia. Find out what causes bleeding between periods.
If you're worried, your community contraceptive clinic, sexual health clinic or genitourinary (GUM) clinic can offer advice, testing and treatment. Find your local clinics.
Sometimes, taking a low-dose contraceptive pill can cause bleeding between periods. This can be corrected by changing pills. Find out about different methods of contraception.
The National Cervical Screening Programme is a scheme to detect abnormalities in the cervix that could lead to cancer if untreated. Women aged 25 to 49 are offered screening every three years. Women aged 50 to 64 are offered it every five years.
If a woman has any bleeding after menopause, this needs urgent attention. "After a woman has had a year with no periods, she should not bleed," says Dr Cassidy. "If you do, seek advice right away. Don't wait to see if it happens again."
Find out about self-help methods to help you cope with menopause.
If your periods suddenly change - for example, they become heavier or longer - get advice. This is especially important for women over 40.
"For most women under 40 with slightly irregular cycles, these symptoms do not have a serious cause," says Dr Cassidy.
"But in women over 40, if periods become much heavier, or are lasting longer, or if they're having erratic bleeding, this needs to be investigated."
Changes in women over 40 can be associated with endometrial cancer, cervical or endometrial polyps, or a pre-cancerous condition (hyperplasia), which can be treated if caught early.
It's normal to have vaginal discharge (secretions), and it's normal for the discharge to change during the menstrual cycle.
"A clear or creamy white discharge is normal, and often makes slightly yellowish stains on the underwear," says Dr Cassidy. Around ovulation, the discharge becomes stretchy, a bit like raw egg white.
See a doctor if you have discharge that's green, blood-stained or smells, as this could be a sign of infection.