The menstrual cycle is one of the main indicators of female health. Although many women believe that their period needs to happen on the exact same day or every 28 days, slight variations are considered normal. Still, frequent changes can be a sign that something deserves attention.

The search “Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles”published in the scientific journal NPJ Digital Medicine, from the Nature group, analyzed data from more than 600,000 menstrual cycles recorded by around 124,000 users of monitoring applications and showed that cycle variation is more common than one might imagine.

In the study, the average cycle was approximately 29 days, with great variability between participants. The research also identified that many women experience natural fluctuations in the interval between menstruations over time, reinforcing that the idea of ​​a fixed 28-day cycle does not represent the reality of the majority of the female population.

“In general, we consider the menstrual cycle to be regular, occurring at intervals of 21 to 35 days. Small variations can occur throughout life and do not always indicate a problem. However, when changes become frequent, such as recurrent delays, very irregular cycles or absence of menstruation for several months, it is always important to seek medical evaluation to investigate the possible causes”, explains Adriana Bittencourt Campaner, gynecologist and colposcopist at Dasa and Alta Diagnósticos, a brand premium from Dasa, a diagnostic medicine company.

Causes of irregular menstruation

What many people know as irregular menstruation is technically classified as abnormal uterine bleeding, a condition that can appear at different stages of a woman’s life. According to Jaime Kulak, gynecologist at the Frischmann Aisengart laboratory in Curitiba, the causes are generally divided between hormonal factors: thyroid dysfunction, polycystic ovary syndrome (PCOS) and the transitions of puberty or menopause; and anatomical causes, linked to structures such as polyps, fibroids and endometriosis.

“These variations can have different origins, from hormonal imbalances to structural issues in the uterus. In rarer cases, it is essential to also investigate hematological causes, such as coagulation disorders, which can directly impact the menstrual flow pattern”, explains the doctor, who adds: “Observing changes in the menstrual cycle can help to identify possible changes early. hormonal changes or gynecological […]”.

Factors that affect the menstrual cycle

Below, doctors list factors that can influence the menstrual cycle. Check it out:

1. Stress can delay your period

Situations of intense stress can interfere with hormone production and temporarily alter the menstrual cycle.

2. Changes in body weight also impact the cycle

Weight gains or losses greater than 5% to 10% of body weight in a few months (about 3 to 6 months) can affect hormonal balance and cause menstrual irregularities. This occurs because rapid changes in body composition influence the production of hormones such as estrogen and leptin, which participate in regulating the menstrual cycle. For this reason, both very accelerated weight loss and rapid weight gain can interfere with the regularity of menstruation.

3. PCOS is a common cause of menstrual cycle irregularity

Polycystic ovary syndrome (PCOS) is one of the gynecological conditions most often associated with irregular menstrual cycles, which can cause frequent delays or absence of menstruation. “To investigate polycystic ovary syndrome, imaging tests are essential. With transvaginal ultrasound, we are able to accurately assess ovarian volume and the presence of small follicles in the organ”, explains Martha Calvente, gynecologist at CDPI and Alta Diagnósticos, in Rio de Janeiro.

She details that imaging is essential for a complete diagnosis. “More than just identify the ‘cysts’the image allows us to exclude other pathologies and monitor the endometrium’s response to hormonal fluctuations typical of PCOS, ensuring safe and personalized monitoring for women’s reproductive and metabolic health.”

4. Thyroid changes can interfere in menstruation

Thyroid problems can also impact hormonal functioning and alter the regularity of the menstrual cycle. Conditions such as hypothyroidism and hyperthyroidism can cause changes in the frequency or intensity of menstruation.

Therefore, when thyroid dysfunction is suspected, laboratory tests that evaluate hormones such as TSH, T3 and T4 are essential to investigate the cause of irregularities and guide treatment.

5. Contraceptives can change menstrual patterns

The introduction or change of hormonal contraceptive methods may cause temporary changes in the frequency, duration or intensity of menstruation. This happens because these medications act directly on the regulation of hormones that control the menstrual cycle.

Combined contraceptives that contain estrogen (usually ethinyl estradiol) associated with progestins such as levonorgestrel, desogestrel or drospirenone usually help regularize the cycle and reduce the menstrual flow over time.

Methods that use only progestogen, such as the mini-pill, hormonal implants or some intrauterine devices (hormonal IUD with levonorgestrel), can cause greater menstrual irregularity in the first months of use, including spotting, frequent bleeding or even absence of menstruation.

These changes are generally expected during the body’s adaptation period, which can last between three and six months. If irregularities persist or cause discomfort, medical evaluation is recommended. In these cases, laboratory tests that evaluate the hormonal profile, such as FSH, LH, estradiol and progesterone, can help investigate the cause of changes in the cycle and guide clinical monitoring.

6. Changes in the uterus or tubes can also influence

In some cases, irregularities may be associated with structural changes in the reproductive system, such as uterine myomatosis, adenomyosis, endometriosis, among others. When there are symptoms such as pelvic pain, heavy bleeding or difficulty getting pregnant, the doctor may order specific tests to investigate the health of the uterus and tubes. One of them is hysterosalpingography (HSG), an imaging test that allows the identification of possible obstructions or anatomical changes.

Tracking the cycle helps identify changes

Writing down your period date or using tracking apps can help you notice patterns and identify important changes. If the menstrual cycle remains dysregulated for several months, the recommendation is to seek a gynecological evaluation to investigate possible causes and receive appropriate guidance.

By Mariana Durante