Periods (Menstruation): What They Are, How They Happen, and What Is Considered Normal

Periods are the part of the menstrual cycle when blood flows from the vagina for several days. Calmly and factually, we explain how this works, what symptoms occur, and where the boundary of normal lies.

What periods and menstruation are

Menstruation, periods, "that time of the month" — this is normal vaginal bleeding that occurs as part of the monthly cycle. Every month the body prepares for pregnancy; if it does not occur, the uterus sheds its inner layer — the endometrium — and it exits through the vagina along with blood and tissue. A new cycle begins on the first day of menstruation.

Menstrual blood barely clots, it contains little fibrinogen, and it is darker than venous blood: the color is explained by the blood "aging" in the vagina. There are no periods during pregnancy, and in most cases they do not occur during breastfeeding either.

Why periods happen: how the menstrual cycle works

The cycle is counted from the first day of one menstruation to the first day of the next. In most women it lasts about 28 days, but both shorter and longer are normal: the range is 21–35 days. Only 13% of women have a cycle of exactly 28 days.

The first period (menarche) usually arrives at 9–15 years of age. The one after the first may come in 2–3 months, and it sometimes takes several years for the cycle to become established. Periods last about 2–8 days. The volume of fluid per cycle averages 50–100 milliliters, with a range from 10 to 250 milliliters. Periods continue until menopause: the normal range is 40–57 years, most often 50–52 years.

Signs that your period is approaching

A few days before it begins, hormone levels change, and this can be felt both in the body and in mood — this condition is called premenstrual syndrome (PMS). Typical signs: bloating, breast tenderness and soreness, mood swings, irritability, skin breakouts, decreased libido, headache. Estimates of PMS prevalence range from 3% to 30%, and not everyone who has periods experiences it. Usually symptoms ease with the onset of menstruation and disappear within a few days.

What happens during periods: symptoms and duration

In addition to bleeding, during periods there may be cramps and pain in the lower abdomen or pelvic area, lower back pain, bloating, breast tenderness, headache, fatigue, and mood swings. Before periods, irritability, drowsiness, fatigue, and a slight increase in heart rate are sometimes noted; during them, a slight slowing of the heart rate.

Bleeding is usually heaviest in the first two days, and the blood is red then. On lighter days it may be pink or brown.

What is considered normal for a menstrual period

It is normal if:

• the cycle lasts from 21 to 35 days;
• periods last from 2 to 7 days, most often about 5;
• about 20–90 milliliters of blood is lost during a period (roughly 1–5 tablespoons);
• the first period came at 9–15 years of age, and periods became regular by 16–18 years;
• menstruation stopped at 40–57 years.

If your numbers fall outside these ranges, it is not yet a diagnosis. But noticeable changes — periods becoming longer, shorter, heavier, or disappearing — are a reason to discuss them with a doctor.

When to see a doctor

Cycle disorders have different names: amenorrhea — no periods, oligomenorrhea — periods coming less often than usual, menorrhagia — very heavy periods, dysmenorrhea — painful periods with cramps. Bleeding between periods, after sex, and after menopause requires particular attention: its cause may be an infection, changes in the cervix, and in rare cases cancer.

If a period has not come and you have been sexually active, pregnancy is possible. If the test is negative and you have missed three periods in a row, a doctor will determine the cause. Another reason to visit is bleeding lasting longer than 8 days, blood loss of more than 80 milliliters, or severe pain. The doctor may order hormone tests, such as estrogen and FSH, and ask you to track your cycle in a calendar.

Periods by themselves are not a reason to call an ambulance; 103/112 — if the condition is life-threatening.

This text is for reference: it helps you understand what is happening to you, but it does not replace a doctor's consultation, which takes your specific situation into account.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer