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Periods are called irregular when the gap between them, the length of bleeding or the amount of flow changes from your usual pattern or falls outside the normal range. Most causes are manageable, and many are temporary, such as stress, a big change in weight or a new contraceptive.
This guide explains what a normal cycle looks like, the common causes, which tests doctors use, and how irregular periods are treated.
What is a normal menstrual cycle?
A cycle is counted from the first day of one period to the first day of the next. The NHS says the average is about 28 days, though a little shorter or longer is common. Cleveland Clinic gives a normal range of 21 to 35 days, and the US National Institute of Child Health and Human Development (NICHD) notes that teenage cycles can range from 21 to 45 days. A period usually lasts about 4 to 7 days. Cleveland Clinic says a cycle is still regular if it varies slightly from month to month.
Irregular periods are most common in the first years after periods begin and in the years before menopause, according to the NHS.
What counts as irregular?
Sources set slightly different limits, so use these as a guide, not strict rules:
- Periods less than 21 days apart or more than 35 days apart (NHS and Cleveland Clinic)
- Three or more missed periods in a row (Cleveland Clinic and NICHD)
- Cycle length that changes by more than 9 days from one cycle to the next (Cleveland Clinic)
- Periods lasting longer than 7 days
- Flow that is much heavier or lighter than usual
- Bleeding or spotting between periods or after sex
- Very painful periods with vomiting or severe cramps
Missing one or two periods is usually not a worry, but first consider pregnancy, which is a common cause of a missed period.
Common causes
Life stage and daily life
- Puberty and perimenopause. Hormones are still settling or starting to change. Perimenopause usually begins around the mid to late 40s, according to the NHS.
- Pregnancy and breastfeeding. Periods may stop or be unpredictable.
- Stress and anxiety.
- Large weight loss or gain, or very low body fat from intense exercise or an eating disorder.
Medical causes
- PCOS (PCOD). Eggs are not released regularly. Read our guide to PCOD vs PCOS.
- Thyroid problems, an overactive or underactive thyroid.
- High prolactin, uncontrolled diabetes or primary ovarian insufficiency (early loss of ovarian function), listed by NICHD and Cleveland Clinic.
- Fibroids, polyps and endometriosis, which often change bleeding patterns or add pain.
- Scarring in the womb or pelvic infection.
Medicines and contraception
Hormonal pills, injections, implants and hormonal coils can all change your bleeding pattern. Cleveland Clinic says irregularity can continue for up to six months after stopping birth control pills. Some other medicines, including blood thinners and certain mental health medicines, can also affect periods. Never stop a prescribed medicine without advice.
When to be cautious: do not assume irregular periods are only stress. If they come with heavy bleeding, bleeding after sex or after menopause, weight changes you cannot explain, or trouble getting pregnant, get them checked.
How doctors find the cause
Your doctor will ask about your cycle, medicines, weight, stress and family history and will examine you. Common tests, per NICHD and Cleveland Clinic, include:
- Pregnancy test if there is any chance of pregnancy.
- Blood tests for hormones such as thyroid and prolactin, blood sugar and iron levels.
- Pelvic ultrasound to look at the ovaries, womb lining, fibroids, polyps or cysts.
- Endometrial biopsy or hysteroscopy in some cases, to look inside the womb or sample the lining.
Tip: track your periods for at least 3 months. Note the first and last day of bleeding, how heavy it was, clots, pain and spotting. A phone calendar or a simple notebook works, and it helps the doctor greatly.
Treatment options
The NHS stresses that treatment is not always needed. When it is, it depends on the cause. Your doctor may suggest:
- Lifestyle steps such as steady, nutritious meals, moderate exercise, sleep, stress management and avoiding rapid weight loss.
- Treating the cause, for example thyroid medicine for a thyroid disorder, or managing diabetes.
- Hormonal treatment to regulate cycles, for example in PCOS. NICHD lists oral contraceptives and cyclic progestin as options for absent or infrequent periods.
- Medicines to reduce heavy bleeding or ease pain, when those are the problem.
- Procedures or surgery for structural causes such as polyps or fibroids if medicines do not help.
- Fertility care if you are trying to conceive and are not ovulating regularly.
Do not start hormonal pills or supplements on your own. They are not suitable for everyone and can hide a condition that needs treatment.
Irregular periods and pregnancy planning
Irregular cycles make ovulation harder to predict. The NHS suggests that if you are trying to conceive, having sex every 2 to 3 days through the cycle can help. If you have been trying without success, see a doctor. Our ovulation calculator works best with regular cycles, so use it only as a rough guide if yours vary. You can also read about when to seek help for infertility.
When to see a doctor
The NHS says to see a doctor if your periods are irregular or your pattern changes. Seek care soon, or urgently, if you have:
- Soaking a pad or tampon every hour for two to three hours, or passing large clots
- Severe pelvic pain, fever or foul-smelling discharge
- Bleeding between periods, after sex or after menopause
- Periods lasting longer than 7 days
- Three or more missed periods in a row, when you are not pregnant
- Dizziness or fainting
See our page on menstrual disorders and the infertility and reproductive care speciality for support.
Talk to a doctor
If you have questions about your own situation, you are welcome to book an appointment or call us on +91 944 103 0587. Chaitanya Hospital in Kadapa offers 24/7 delivery and emergency care, and teleconsultation is available. This article is for general awareness and is not a substitute for a doctor's advice.
References
This article was written in our own words from the following public health sources.
Educational content
Please note. This article is for general awareness and is not a substitute for a doctor’s advice, diagnosis or treatment. If you are worried about your health, or in an emergency, call +91 944 103 0587 or visit the hospital.
