The timing of a period can change for many reasons. Pregnancy needs consideration when it is possible. A clinician can then look at the pattern, associated symptoms, medicines and health history to decide whether you need advice, tests, imaging or another route.
What counts as irregular?
NHS describes periods as irregular when the gap between them is less than 21 days or more than 35 days. The usual gap is around 28 days, although it can be shorter or longer.[1]
Keep a record of the first day of each period, the gap until the next period, bleeding between periods, pain and any new symptoms. A diary or app can make a change in your normal pattern easier to describe at an appointment.[1]
Common contexts and possible causes
Puberty and the approach to menopause can change cycle timing. Pregnancy, hormonal contraception, substantial weight loss or gain, stress and high exercise levels can also affect periods. NHS also lists polycystic ovary syndrome and thyroid problems as possible causes.[1]
The pattern alone cannot identify the cause. For example, facial hair growth, acne, weight change or tiredness may guide the questions a clinician asks, but they cannot confirm a diagnosis by themselves.
Cycle timing
A new pattern, missed periods or a gap that falls outside the usual range needs context.
Bleeding changes
Bleeding between periods, bleeding after sex, heavy bleeding or periods lasting more than 7 days should be discussed with a clinician.
Associated symptoms
Pelvic pain, tiredness, a change in weight, facial hair growth, headaches or discharge may affect the investigation route.
Pregnancy plans
Irregular cycles may make ovulation less predictable. Tell the clinician if you are trying to conceive.
How an assessment is tailored
A clinician uses the information below to choose a proportionate next step. An irregular period does not mean that each person needs the same blood tests or scan.
Pattern and timing
A period diary can record cycle dates, bleeding changes and symptoms. NHS suggests tracking periods to help show whether the pattern is irregular.
Pregnancy possibility
A missed or changed period can be an early sign of pregnancy. Tell the clinician if pregnancy is possible, including if you have used contraception.
Medical and medicine history
Contraception, recent weight change, exercise, stress, medicines and symptoms such as tiredness, facial hair growth or pelvic pain can shape the next step.
Tests and imaging
A clinician may recommend tests or imaging for a specific question. NICE says the choice between ultrasound and hysteroscopy for heavy bleeding should follow the history and examination.
For heavy menstrual bleeding, NICE says clinicians should use the history and examination to choose whether ultrasound or hysteroscopy is the first investigation. NICE also advises against routine female-hormone testing for heavy menstrual bleeding, and against thyroid tests unless other signs and symptoms suggest thyroid disease.[4]
Menopause and changing periods
Cycle changes can occur during perimenopause. Hormone blood tests are not routinely needed to diagnose menopause in otherwise healthy women aged 45 or over with menopause-associated symptoms. NICE advises that testing may be appropriate in younger women, atypical presentations, or where another diagnosis is being considered.[2]
NICE says not to use AMH, oestradiol, antral follicle count or ovarian volume to identify perimenopause or menopause in people aged 45 or over. A clinician may consider FSH in people aged 40 to 45 with menopause-associated symptoms and cycle changes, or in people under 40 where menopause is suspected.[2]
Any bleeding after menopause, persistent bleeding between periods or bleeding after sex needs assessment. Seek medical advice rather than assuming menopause is the cause.
Pregnancy and urgent symptoms
A missed or altered period can be an early sign of pregnancy. Contact your GP or NHS 111 if pregnancy could be possible and you have vaginal bleeding with lower tummy pain, even if you have not had a positive pregnancy test. NHS advises urgent medical advice for those symptoms because ectopic pregnancy needs assessment.[3]
Call 999 or go to A&E if pregnancy could be possible and you develop sudden, sharp, intense tummy pain with dizziness or fainting. NHS identifies these as symptoms of possible ectopic-pregnancy rupture.[3]
Do not wait for a routine appointment
Use 999 or A&E for the pregnancy-related emergency symptoms above. Use NHS 111 or contact your GP for pregnancy-related bleeding and lower tummy pain that needs prompt advice.
When to seek an assessment
NHS advises speaking to a GP if periods are irregular, last more than 7 days, occur with symptoms such as weight gain, tiredness, facial hair growth or oily or dry skin, include bleeding between periods, or if irregular cycles are making it difficult to get pregnant.[1]
Care can begin with your GP or a gynaecology route, depending on the problem and availability. The clinic confirms the appropriate route, suitability, referral needs, availability, preparation, reporting and follow-up at booking.
Questions to take to an appointment
Could pregnancy be relevant to my changed period?
Which parts of my period pattern and symptoms should I record?
Do my symptoms point to a reason for targeted blood tests or imaging?
Does contraception or another medicine affect the interpretation?
Does my age and symptom pattern change the menopause assessment?
What should I do if pain, bleeding or another symptom becomes more severe?
Frequently asked questions
What counts as an irregular period?
NHS describes periods as irregular when the gap between them is less than 21 days or more than 35 days. A new change in your normal pattern also deserves attention.
Should I take a pregnancy test?
Consider pregnancy if a period is late or different from usual. If you have bleeding and lower tummy pain and pregnancy could be possible, seek medical advice through your GP or NHS 111. Sudden intense tummy pain with dizziness or fainting needs 999 or A&E.
Do I need a hormone panel to diagnose menopause?
In otherwise healthy people aged 45 or over with menopause-associated symptoms, NICE identifies perimenopause and menopause without routine laboratory tests. NICE says not to use AMH, oestradiol, antral follicle count or ovarian volume to identify menopause in this group. Blood testing may have a role in younger people, atypical presentations or where another diagnosis is being considered.
Will I need a pelvic ultrasound?
A pelvic ultrasound may be useful for some symptoms, but it is not automatically the right test for every irregular period. A clinician uses your history and, where appropriate, examination to decide whether ultrasound, another test or a different pathway will help.
Can irregular periods affect fertility?
Irregular periods can make it harder to predict ovulation. If you are trying to conceive and your periods are irregular, NHS advises seeking GP assessment. Any fertility investigation and support depend on your circumstances.
When should I seek urgent help?
Call 999 or go to A&E if pregnancy could be possible and you have sudden intense tummy pain with dizziness or fainting. Contact NHS 111 or your GP promptly for bleeding in pregnancy with lower tummy pain, or for symptoms that concern you.