Menstruação irregular: causas, quando se preocupar e o que fazer

An irregular period is one that doesn't follow a predictable pattern — arriving earlier or later than expected, lasting an unusually long or short time, or involving significantly heavier or lighter bleeding than normal. Occasional irregularity is extremely common and usually not cause for alarm. But persistent changes to your cycle can signal something worth investigating.

According to the Cleveland Clinic, a "normal" menstrual cycle falls anywhere between 21 and 35 days in length, with bleeding lasting 3–7 days. If your cycle consistently falls outside these parameters, it's considered irregular.

What Counts as Irregular?

Your period may be considered irregular if:

• Your cycles are consistently shorter than 21 days or longer than 35 days
• The length of your cycle varies significantly from month to month (e.g., 25 days one month, 38 days the next)
• Your period lasts more than 7 days
• Your bleeding is very heavy (soaking a pad or tampon every hour for 2+ hours)
• You experience spotting or bleeding between periods
• You miss periods entirely (amenorrhea) without pregnancy

Occasionally having your period arrive a few days off schedule is normal and usually not concerning. It's the consistent, persistent patterns that deserve attention.

Common Causes of Irregular Periods

1. Stress

Stress is one of the most common and frequently underestimated causes of cycle irregularity. When you're under significant psychological or physical stress, your body produces more cortisol. Elevated cortisol can suppress the production of GnRH (gonadotropin-releasing hormone), which disrupts the hormonal cascade needed for ovulation — leading to delayed or skipped periods.

2. Significant Weight Changes

Both rapid weight loss and substantial weight gain can disrupt the hormonal signalling that regulates your cycle. Body fat plays a role in estrogen production, so very low body weight (common in athletic or restrictive eating contexts) can cause periods to become infrequent or stop. On the other end, obesity is associated with excess estrogen production, which can also disrupt cycle regularity.

3. Polycystic Ovary Syndrome (PCOS)

PCOS is the most common hormonal disorder affecting reproductive-age people, estimated to affect 5–10% of women. It's characterised by elevated androgen levels, irregular ovulation, and often (though not always) ovarian cysts. PCOS frequently causes irregular, infrequent, or absent periods, and is one of the first conditions doctors investigate when evaluating irregular cycles.

Other symptoms of PCOS can include acne, excess facial or body hair, weight gain, and difficulty losing weight.

4. Thyroid Disorders

Both an underactive thyroid (hypothyroidism) and overactive thyroid (hyperthyroidism) can disrupt the menstrual cycle. The thyroid regulates metabolism and influences sex hormone binding globulin levels, which affects how estrogen and progesterone are processed. Thyroid disorders are among the most commonly missed causes of menstrual irregularity — a simple blood test can check your thyroid function.

5. Perimenopause

In the years leading up to menopause (typically the mid-40s to early 50s, though sometimes earlier), fluctuating and declining estrogen levels can cause cycles to become irregular — sometimes shorter, sometimes longer, sometimes heavier or lighter. Hot flashes, sleep disruption, and mood changes often accompany perimenopausal cycle changes.

6. Endometriosis

Endometriosis occurs when tissue similar to the uterine lining grows outside the uterus. It can cause heavy, painful periods and sometimes irregular bleeding between cycles. It affects approximately 1 in 10 people with a uterus and is notoriously difficult to diagnose — the average diagnostic delay is 7–10 years.

7. Uterine Fibroids or Polyps

Fibroids are non-cancerous growths in the uterus that can cause heavy or prolonged bleeding, as well as pressure and pain. Uterine polyps are small growths of the uterine lining that can cause irregular spotting or heavy periods. Both can be detected via pelvic ultrasound.

8. Medications and Contraceptives

Certain medications can affect cycle regularity, including antidepressants, antipsychotics, blood thinners, and chemotherapy agents. Starting or stopping hormonal contraceptives can also cause temporary cycle irregularity while the body adjusts.

9. Intense Exercise

Athlete amenorrhea, or exercise-associated menstrual dysfunction, occurs when very high exercise volumes — particularly in combination with calorie restriction — suppress the hormonal axis that drives ovulation. Female athletes in endurance or aesthetic sports are particularly susceptible.

10. Illness or Surgery

Acute illness, including respiratory or gastrointestinal infections, can temporarily disrupt the ovulation process and delay your period. Major surgery or hospitalisation can have a similar effect.

When to See a Doctor

Occasional irregularity is usually nothing to worry about. However, you should schedule an appointment with your GP or gynaecologist if:

• You consistently have cycles shorter than 24 days or longer than 35 days
• You go more than two months between periods and are not pregnant
• Your periods are consistently lasting longer than 7 days
• You're soaking through a pad or tampon every hour for several hours
• You have severe pelvic pain during or between periods
• You notice bleeding after sex or between periods
• You've missed 3 or more consecutive periods
• You're trying to conceive and suspect irregular ovulation

What Your Doctor May Check

Diagnosing the cause of irregular periods typically involves a combination of:

• A detailed menstrual history (this is where your tracking data becomes invaluable)
• Blood tests for thyroid function, FSH, LH, estrogen, testosterone, and prolactin levels
• A pelvic ultrasound to check for fibroids, polyps, ovarian cysts, or PCOS-related changes
• Sometimes an endometrial biopsy if abnormal bleeding is a concern

How Tracking Helps

The single most useful thing you can do before a medical appointment is bring at least 3 months of detailed cycle data. Noting your cycle start and end dates, flow intensity, pain levels, and associated symptoms gives your doctor a clear picture rather than a vague description.

Your Rhythm makes it easy to track all of this automatically and generate a summary you can share at appointments. Available on iOS and Android, Your Rhythm gives you a structured log of cycle dates, flow, and symptoms that builds over time. The difference between "my periods have been irregular lately" and "here are my last 6 cycles with flow levels, pain scores, and symptom logs" is enormous in terms of diagnostic efficiency.

Understanding your cycle's baseline is the first step to identifying when something has changed — and getting the answers you deserve.