Everything You Need To Know About Menstruation

Every day, 800 million women and girls around the world are menstruating. Here’s what you need to know about this complex yet common occurrence.

Menstruation is the shedding of the uterine lining.

Every month the uterus regrows its lining in preparation for a fertilized egg to implant in it. If an egg hasn’t been implanted on the uterine wall by the time the lining is done growing, the lining begins to shed, makes its way through the OS (the opening between the uterus and the vagina), and causes the vaginal bleeding we refer to as a “period.”

The menstrual cycle has three phases.

The menstrual cycle can be broken down into three phases. The first phase begins on the first day of the period, and it’s called the follicular phase. During this phase, the ovary prepares the egg that will be released approximately 14 days later during the second phase, which is called ovulation.

After ovulation, the luteal phase begins in which the body prepares the uterine lining for fertilization. If the egg is not fertilized by the end of this third phase, the uterine lining begins to shed -- which is the beginning of the next menstrual cycle.

Menarche is when a girl has her first period.

Menarche (pronounced MEN-AR-KEY), is formed from the Greek word meanos, which means, and the Greek word arkhe, which means beginning. In medicine, the term is used to describe a girl’s first period.

The average age of menarche in developed countries is 12 years old, though it’s considered normal for menarche to occur anywhere from 10-16 years of age. 

 “Normal” menstrual cycles can be anywhere from 24-38 days in length.

 While referring to a period as a “monthly cycle” implies that a period occurs exactly once a month, in reality, only 10-15% of women have a cycle that recurs exactly every 28 days.

Some women have a shorter cycle that occurs every 24 days, while some have a longer cycle that occurs every 38 days. These time frames are all within the bounds of normal.

Women can get a better understanding of their cycle -- and when to expect the next one -- by tracking their periods on a calendar or using a period-tracking app.

Most periods last 4-8 days.

The average period lasts for 5 days from start to finish. However, it’s considered normal for periods to be as short as 4 days and as long as 8 days. Women whose periods are heavier than average, longer than normal, or irregular are often prescribed oral contraceptives that can help to regulate their cycle.

Menstruation can cause several other symptoms.

Painful menstrual cramping (called) is one of the most commonly experienced symptoms of menstruation. In fact, 75% of menstruating women report painful cramping just before or during their period. Many women find that using a heating pad and taking an anti-inflammatory over-the-counter medication alleviates their discomfort.

It’s estimated that 75% of menstruating women also experience some form of PMS (Premenstrual Syndrome), a combination of both physical and psychological symptoms. These symptoms can include mood swings, crying spells, food cravings, breast tenderness, and irritability. These symptoms begin anywhere from 5-10 days before a woman gets her period and resolve soon after her period starts.

A more severe form of PMS is called Premenstrual Dysphoric Disorder (PMDD). In addition to the physical symptoms of PMS, PMDD can also cause anger, insomnia, severe fatigue, extreme mood swings, and depression.

It’s thought that PMDD happens when hormones lower a woman’s serotonin levels. Medications that increase serotonin levels (called Selective Serotonin Reuptake Inhibitors or, SSRI’s) are often used to treat PMDD.

Women also need to know when to get their thyroid checked. Low levels of thyroid hormone cause a delay in the breakdown of estrogen as well as a decrease in clotting factors, which means that many women with an underactive thyroid experience heavier-than-normal periods.

Periods increase the risk of anemia.

Menstruation is the number one culprit for iron deficiency anemia in menstruating women. In fact, 42% of women of childbearing age worldwide have iron deficiency anemia.

It’s important for menstruating women to get plenty of iron. They can do this by eating iron-rich foods like beef, oysters, mussels, spinach, and kale. Also, women’s multivitamins and iron supplements can provide women with the iron their bodies need.


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Written by Sarah Thebarge, Physician Assistant