Irregular periods: causes and when to see a doctor

Your period arrived early this month, or it’s a week late and you’re not sure why. Occasional changes are completely normal: very few people have cycles that run like clockwork. But when your periods are often unpredictable, it can be frustrating, and sometimes it’s your body’s way of signaling that something needs attention. Here’s how to tell the difference.

What counts as an irregular period?

For adults, a typical cycle lasts between 21 and 35 days, counted from the first day of one period to the first day of the next. A little variation is expected, but your periods may be considered irregular if:

• Your cycles are regularly shorter than 21 days or longer than 35 days.
• Your cycle length varies by more than 7 to 9 days from month to month, for example 24 days one month and 36 the next.
• You often skip periods or go months without one.

When irregular cycles are expected

Some stages of life naturally come with less predictable cycles:

• Puberty: in the first few years after your first period, cycles are often irregular and can last up to 45 days while your hormones settle.
• Perimenopause: in the years leading up to menopause, usually in your 40s, cycles may become shorter, then longer, and periods may be skipped.
• After pregnancy and while breastfeeding: breastfeeding can delay the return of your periods, and the first cycles may be irregular. You can ovulate before your first period comes back, so talk to a health professional before relying on breastfeeding as contraception.

Common causes of irregular periods

Many things can affect the hormones that control your cycle, including:

• Pregnancy: if you’ve had sex and your period is late, take a pregnancy test first.
• Stress: emotional or physical stress can delay ovulation, and therefore your period.
• Weight changes: significant weight loss or gain, a very low body weight or disordered eating can disrupt ovulation.
• Intense exercise: training hard without eating enough to match your energy needs can make periods irregular or stop them.
• Polycystic ovary syndrome (PCOS): a common hormonal condition that can cause irregular or absent periods, acne, excess hair growth and difficulty getting pregnant.
• Thyroid problems: both an overactive and an underactive thyroid can affect your cycle.
• High prolactin: raised levels of this hormone, sometimes caused by certain medicines or a benign growth on the pituitary gland, can stop ovulation.
• Contraception: starting, switching or stopping hormonal contraception often changes your bleeding pattern for a few months.

How tracking helps

Memory is unreliable when it comes to periods. Logging the start date of each period, how long it lasts and how heavy it is gives you an accurate picture of your real average cycle length and how much it varies. Over time, you may notice links, such as longer cycles after a stressful month or changes after starting a new medicine. Your record also lets a cycle tracking app widen its predictions when your cycles vary, and gives your doctor precise information instead of guesses.

What a doctor might check

A doctor will usually ask about your cycle history, general health, weight changes, stress, exercise and medicines. Depending on your situation, they may suggest a pregnancy test, blood tests to check hormones such as thyroid hormones, prolactin and androgens, and sometimes a pelvic ultrasound. Treatment depends on the cause, and many causes are very manageable once they’re identified.

When to see a doctor

Make an appointment if:

• You haven’t had a period for 3 months and you’re not pregnant.
• You have bleeding between periods or after sex.
• Your periods are very heavy, for example soaking through a pad or tampon every 1 to 2 hours, or you pass large clots.
• Your periods last longer than 7 days, or your cycles are consistently shorter than 21 days or longer than 35 days.
• Irregular periods come with other symptoms, such as excess hair growth, severe acne, milky nipple discharge or unexplained weight changes.
• You’re trying to get pregnant and your cycles are irregular.