Irregular periods in teenagers: what is normal and when is a check-up needed?

English version

Periods may be irregular during the first few years after they begin because the hormonal system controlling ovulation is still maturing. Some variation is expected, but every irregular pattern should not automatically be dismissed as normal.

What may be normal?

During the first one to two years, the interval between periods may vary. A cycle is counted from the first day of one period to the first day of the next. Teenage cycles commonly occur about every 21–45 days, with bleeding generally lasting no longer than seven days. They often become more predictable with time.

When is medical advice recommended?

• Periods have not started by age 15
• There is a gap of 90 days or more, even once
• Periods regularly occur less than 21 or more than 45 days apart
• Bleeding lasts longer than seven days
• Previously regular periods become markedly irregular
• A pad needs changing every one to two hours
• Pain prevents school, sleep or normal activity
• There is bleeding between periods
• The teenager appears pale, tired, dizzy or breathless
• Irregular periods accompany marked acne, excess facial hair or major weight change

What can cause irregular or missed periods?

• Normal hormonal adjustment after the first period
• Stress or disrupted sleep
• Significant weight loss or gain
• Inadequate nutrition or an eating disorder
• Intensive exercise
• Pregnancy
• Hormonal contraception
• PCOS
• Thyroid, prolactin or other hormonal conditions
• Some medicines or chronic illnesses

PCOS should not be diagnosed from irregular periods, acne or an ultrasound alone. These features can overlap with normal early adolescence. Pregnancy testing may be appropriate whenever pregnancy is biologically possible, with a respectful opportunity for confidential discussion within safeguarding requirements.

Can heavy periods cause anaemia?

Yes. Repeated heavy bleeding can reduce iron and haemoglobin, causing tiredness, weakness, headache, dizziness, pale skin, breathlessness, a fast heartbeat or difficulty concentrating. Heavy bleeding from the earliest periods may sometimes indicate a bleeding disorder, especially with frequent nosebleeds, easy bruising or a family history.

What may assessment involve?

The doctor may review menstrual timing, bleeding, pain, weight, diet, exercise, sleep, stress, medicines, acne, excess hair and pregnancy possibility. Selected tests may include pregnancy testing, blood count, iron, thyroid or hormone tests, bleeding-disorder testing and ultrasound. A pelvic examination, ultrasound and broad hormone panel are not automatically required for every teenager.

Is treatment always needed?

No. Tracking and follow-up may be enough when the pattern reflects normal early development and no warning features are present. Treatment depends on the cause and may include iron replacement, nutritional support, treatment of a thyroid or hormonal condition, or medication to control bleeding. Do not start hormonal tablets, high-dose iron or unverified “hormone balance” supplements without individual advice.