Irregular Periods: Causes, Late Periods & When to Worry

A period is called irregular when your cycle is shorter than 21 days, longer than 35 days, or changes in length by more than 7 to 9 days from month to month. The most common causes are PCOS, thyroid problems, high prolactin, stress and sudden weight change, and less often low ovarian reserve or a problem in the womb such as fibroids or polyps. An occasional late or early period is normal, but if your cycles stay unpredictable, a few simple tests usually find the reason. At Yaal Fertility Centre in Chennai, Dr. Rukkayal Fathima and our team see many women with irregular cycles, both those trying to conceive and those who are not.

What Is a Normal Menstrual Cycle?

A cycle is counted from the first day of one period to the first day of the next. A regular cycle usually has:

Doctors also use a few medical terms you may see on a report:

• Oligomenorrhoea: periods more than 35 days apart, or fewer than about 8 periods a year.
• Amenorrhoea: no period for 3 months or more when you are not pregnant. See our guide to amenorrhea.
• Intermenstrual bleeding: bleeding or spotting between periods.

Keeping a note or app record of your period dates for three months gives your doctor the most useful information.

Late Period but Not Pregnant: Common Reasons

A pregnancy test comes first. If you are sexually active and your period is late, take a home urine test, and repeat it after a week if it is negative and your period still has not come.

Once pregnancy is ruled out, a delayed period usually means ovulation happened late or not at all that month. Common reasons:

• Stress: physical or emotional stress raises cortisol, which can hold back the brain hormones that trigger ovulation. Read more on how stress affects fertility.
• Weight change: losing weight quickly, eating too little or being underweight can switch ovulation off. Gaining weight can also unsettle the hormones that control the cycle.
• Heavy exercise: very intense training without enough food can delay or stop periods.
• Illness, travel or a change in routine, including night shifts (see night shift and fertility).
• Breastfeeding: high prolactin while feeding often keeps periods away for months.
• Recent start or stop of hormonal medicines, such as the pill or an emergency contraceptive.
• Life stage: cycles are often irregular in the first few years after periods start, and again in the years before menopause.

If your period is late once and then returns to normal, this is rarely a concern. If it keeps happening, look at the medical causes below.

Irregular Periods at Different Ages

What counts as "normal" changes through life, and so do the likely causes.

Teenagers and the First Few Years

In the first two to three years after periods start, cycles are often irregular because the link between the brain and the ovaries is still maturing. Periods may be 20 days apart one month and 45 the next. This usually settles on its own. See a doctor if periods have not started by 15, if there is no period for 3 months once they have started, if bleeding lasts more than 7 days or is very heavy, or if there are signs of PCOS such as acne and excess hair growth. PCOS often first shows itself in the late teens.

In Your 20s and Early 30s

Cycles are usually at their most regular in these years, so a change is worth noticing. The common causes at this age are PCOS, thyroid problems, high prolactin, stress, weight change and stopping the pill. This is also the age when many women start trying for a baby, and irregular periods are often the first clue to an ovulation problem.

After Childbirth and While Breastfeeding

While you are breastfeeding, the hormone prolactin stays high and can keep periods away for months. When periods return, the first few cycles are often irregular. If you are not breastfeeding, periods usually come back within about 6 to 8 weeks of delivery. You can still ovulate before your first period returns, so you can get pregnant again before you see a period. If periods have not settled within a few months of stopping breastfeeding, a check of thyroid and prolactin is sensible, as thyroid problems are more common after childbirth. Our prenatal and postnatal care team can advise.

In Your 40s: Perimenopause

In the years before menopause, the ovaries respond less evenly. Cycles often become shorter at first, then longer and less predictable, and periods may get heavier. Hot flushes, night sweats, poor sleep and mood changes are common. Menopause is confirmed when you have had no period for 12 months, at an average age of about 46 to 47 in India, a little earlier than in Western countries. Heavy, very frequent or prolonged bleeding in your 40s should still be checked, because fibroids, polyps and a thickened lining become more common at this age. See our menopause care.

Medical Causes of Irregular Periods

Most of these are hormonal. For the full list of signs to look out for, see hormonal imbalance symptoms in women.

PCOS

Polycystic ovary syndrome (PCOS) is the most common hormonal cause of irregular periods in women of reproductive age. Higher levels of male-type hormones (androgens) and insulin stop follicles from maturing properly, so ovulation becomes infrequent. Periods may be months apart, then heavy when they come. Other signs include acne, excess facial or body hair, weight gain around the waist and difficulty losing weight. Read more in PCOS and fertility and about our PCOS care.

Thyroid Problems

• An underactive thyroid (hypothyroidism) can cause heavy, long or delayed periods, tiredness, weight gain and feeling cold.
• An overactive thyroid (hyperthyroidism) can cause light or infrequent periods, weight loss, palpitations and anxiety.

Both are easy to test for with a TSH blood test and usually easy to treat. See thyroid and fertility.

High Prolactin

Prolactin is the hormone that makes breast milk. When it is high outside pregnancy and breastfeeding, it can delay or stop periods, and sometimes causes a milky nipple discharge. Causes include some medicines, an underactive thyroid and a small, usually harmless, pituitary growth. See hyperprolactinemia and fertility.

Low Ovarian Reserve or Early Menopause

When the ovaries run low on eggs before 40, a condition called premature ovarian insufficiency, periods become irregular and then may stop, often with hot flushes or night sweats. An AMH and FSH test help confirm it. See premature ovarian failure and fertility options.

Problems in the Womb

Some causes affect the bleeding pattern rather than the timing of the cycle:

• Fibroids can cause heavy or long periods. See fibroids and fertility.
• Polyps can cause spotting between periods or after sex. See uterine polyps.
• Endometriosis and adenomyosis often cause painful, heavy periods. See endometriosis and fertility.
• Infection such as pelvic inflammatory disease can cause irregular bleeding and pelvic pain.

Any bleeding after sex, between periods or after menopause should always be checked by a doctor.

PCOS, Thyroid or Prolactin: How They Differ

The three most common hormonal causes can look alike, but each has its own pattern of clues:

More than one cause can be present at the same time, for example PCOS with a mild thyroid problem, which is why doctors usually check all three together.

Do Irregular Periods Affect Fertility?

They can, because an irregular cycle usually means irregular or absent ovulation. If you do not release an egg every month, there are fewer chances to conceive in a year, and it is harder to know when your fertile days are.

Home methods are less reliable with irregular cycles:

• Ovulation kits may show repeated positive results in PCOS without an egg being released.
• Temperature charts only show that ovulation has already happened.
• Counting days does not work when cycle length keeps changing. See the phases of the menstrual cycle for how ovulation timing normally works.

A follicular study (a series of ultrasound scans over a few days) shows whether an egg is growing and when it is likely to be released, so you can time intercourse or treatment accurately. Many women with irregular periods conceive once the cause is treated or ovulation is supported. Our guide to the chances of getting pregnant by cycle day explains the fertile window.

How to Track an Irregular Cycle at Home

A simple record is the most useful thing you can bring to your first appointment. For at least three months, note:

• The first day of each period and how many days you bleed.
• How heavy the flow is, for example how many pads you use on the heaviest day, and whether there are clots.
• Spotting between periods or after sex.
• Pain, and whether it stops you from working or studying.
• Other changes, such as acne, hair growth, weight change, tiredness or mood.

A period-tracking app or a calendar both work well. If you are trying to conceive, you can also note changes in vaginal discharge: clear, stretchy discharge like raw egg white usually means ovulation is near.

Do not rely on an app's "fertile days" prediction if your cycles are irregular. Apps estimate ovulation from your average cycle length, which is unreliable when cycles vary a lot. Ovulation kits or a follicular scan give a far better answer.

What to Expect at Your Gynaecologist Visit

Many women delay seeing a doctor because they are unsure what will happen. A first visit for irregular periods is usually straightforward.

Questions Your Doctor Will Ask

• When your periods started, and when they became irregular.
• Your usual cycle length, how long you bleed, and how heavy it is.
• Whether you are trying to conceive, or need contraception.
• Changes in weight, skin, hair, sleep, stress or exercise.
• Medicines you take, and any thyroid, diabetes or PCOS in your family.

Examination and Tests

Your doctor may check your weight, blood pressure and signs such as acne or excess hair. A pelvic ultrasound is often done, usually transvaginally for a clearer picture. For women who have never been sexually active, a scan through the tummy is used instead. Blood tests are then planned, some on specific days of your cycle, as listed below. Most women leave the first visit with a clear plan for testing and, often, the likely cause.

Tests for Irregular Periods

A gynaecologist usually starts with your history and then suggests:

• Pregnancy test (urine or blood hCG).
• TSH for thyroid function.
• Prolactin.
• FSH and LH, taken on day 2 to 4 of your period where possible.
• AMH to check ovarian reserve.
• Testosterone if PCOS is suspected.
• A pelvic ultrasound, usually transvaginal, to look at the ovaries, the womb lining and any fibroids or polyps.

Treatment for Irregular Periods

Treatment depends on the cause and on whether you want to get pregnant now.

If you are not trying to conceive:

• Lifestyle changes (see the steps below). In PCOS, losing even 5 to 10% of body weight often brings back ovulation.
• Thyroid medicine for a thyroid problem, or medicine to lower prolactin when it is high.
• Hormonal treatment, such as the combined pill or a cyclical progestogen, to regulate bleeding and protect the womb lining.
• Treatment of fibroids or polyps where they cause heavy or irregular bleeding.

If you are trying to conceive:

• Treating the underlying cause first, such as thyroid or prolactin problems.
• Ovulation induction with tablets such as letrozole, monitored with follicular scans, and injections if tablets do not work.
• IUI or IVF where there are other factors, such as blocked tubes or a low sperm count.

Diet and Lifestyle Steps That Help

• Keep a steady weight. Both being underweight and carrying extra weight around the waist can stop regular ovulation.
• Eat regular, balanced meals. Build meals on millets, whole grains, vegetables, dal and other protein, and cut down on sugar, white rice and maida. Our PCOS diet guide has South Indian meal ideas.
• Move most days. Brisk walking or yoga for about 30 minutes is enough; very intense training without enough food can make things worse.
• Sleep and stress. Regular sleep and time to unwind help the brain hormones that control ovulation.

Lifestyle steps support treatment, but they do not replace finding the cause. Thyroid and prolactin problems, for example, need medical treatment.

Common Myths About Irregular Periods

"Irregular periods mean I cannot have children." Not true. Many women with irregular cycles conceive naturally, and most causes are treatable.

"It is normal, so there is no need to see a doctor." An occasional late period is normal. Cycles that are regularly irregular usually have a cause worth finding, because some, such as PCOS and thyroid disease, also affect long-term health.

"Skipping periods is harmful because the blood builds up inside." Blood does not collect inside the body. However, going many months without a period can let the womb lining build up under estrogen, which is why doctors sometimes prescribe treatment to bring on a period.

"Home remedies like papaya or sesame will bring on a period." There is no good evidence that particular foods start a period. If your period is late, rule out pregnancy and find the reason.

"Only overweight women get PCOS." PCOS also affects women of normal weight, so a normal BMI does not rule it out.

When to See a Doctor About Irregular Periods

Book an appointment if:

• You have not had a period for 3 months and you are not pregnant.
• Your cycles are regularly shorter than 21 days or longer than 35 days.
• Your periods last more than 7 days, or you soak a pad every hour for several hours.
• You bleed between periods or after sex.
• You have severe period pain, or signs of PCOS such as excess hair growth.
• You have been trying to conceive for 12 months (or 6 months if you are over 35). With irregular periods, it is reasonable to see a doctor sooner.