What Causes Menstrual Irregularities?

Menstrual irregularity is one of the most frequent reasons women consult a physician. Not every change in the cycle means disease, but some irregularities can be the first sign of an underlying condition. This article summarises the normal limits of the cycle and the possible causes of irregularity.

What is a normal cycle?

The cycle is counted from the first day of one period to the first day of the next. According to the definitions of the International Federation of Gynecology and Obstetrics (FIGO), a cycle length of 24–38 days, bleeding lasting up to 8 days and cycle-to-cycle variation of up to 7–9 days are considered normal. Greater variability is expected in the first years after menarche and in the years approaching menopause.

Types of irregularity

• Infrequent periods (oligomenorrhoea): cycles longer than 38 days
• Frequent periods (polymenorrhoea): cycles shorter than 24 days
• Absent periods (amenorrhoea): no bleeding for three months or more
• Heavy bleeding (menorrhagia): bleeding lasting more than 8 days or heavy enough to affect daily life
• Intermenstrual bleeding: spotting or bleeding between periods

Common causes

Hormonal: polycystic ovary syndrome (PCOS), thyroid disorders, raised prolactin and the menopausal transition are the most frequent hormonal causes.

Structural: endometrial polyps, fibroids, adenomyosis and intrauterine adhesions can cause heavy and prolonged bleeding in particular.

Lifestyle and general health: rapid weight gain or loss, excessive exercise, sleep disorders, intense stress and some chronic diseases can affect the cycle.

Medication and contraception: hormonal contraceptives, intrauterine devices, anticoagulants and some psychiatric drugs can change the bleeding pattern.

Pregnancy: in women of reproductive age, pregnancy is the first cause to consider when a period is late; ectopic pregnancy and miscarriage can also present with irregular bleeding.

When to see a physician

• No period for more than three months (once pregnancy has been excluded)
• Cycles consistently shorter than 21 or longer than 38 days
• Bleeding that requires changing a pad or tampon every hour, or large clots
• Bleeding after intercourse or after menopause
• Bleeding accompanied by severe pain, dizziness or weakness

How is it assessed?

The physician first asks about the menstrual calendar, the amount of bleeding, accompanying symptoms and medication. The uterus and ovaries are assessed by gynaecological examination and ultrasound. A pregnancy test, full blood count, thyroid and other hormone tests may be requested where appropriate. Identifying the cause allows treatment to be planned individually; it is the underlying cause, not the irregularity itself, that is treated.

A practical tip: track your cycle

Recording the start and end dates of bleeding, its amount and any pain in a calendar or app makes the physician’s assessment much easier. A record of at least three cycles helps define the type of irregularity.