Menstruation

The menstrual cycle is a process most females go through each month that prepares the body for pregnancy. It includes the growth and selection of follicles that each hold an egg, the release of one egg from an ovary, and getting the uterus ready for an embryo. If no embryo arrives to the uterus, then menstruation happens and the cycle restarts.

All people with ovaries are born with a finite number of egg cells. After puberty, these follicles grow in waves. Every menstrual cycle, some of the bigger follicles are chosen to grow and one may be chosen to ovulate.Then, during ovulation, one of those eggs gets released from its follicle and the ovary. The shell of the follicle that is left behind releases hormones that tell the uterus what to do (this is called the luteal phase). If the egg doesn't meet a sperm cell and get fertilized, then menstruation, or a period, happens. During a period, blood comes out of the vagina, which signals the beginning of a new menstrual cycle.

Having a regular menstrual cycle is a sign of health and fertility. Most girls have their first menstrual cycle between ages 9 and 17, or when they reach puberty (which can be earlier or later). From that moment on, that girl usually experiences a menstrual cycle every month or so. That continues through her life until she reaches menopause around age 51. Menopause is when the ovaries stop making hormones, so no more eggs develop or ovulate.

Menstruation (or a period) is the regular monthly bleeding that signals the start of a new menstrual cycle. It marks the beginning of the follicular phase of the menstrual cycle. During a period, the inner lining of the uterus (endometrium) sheds through the vagina over a span of several days. The contractions of the uterus that cause this are due to the prostaglandins, which are lipids (fats) that are often found near damaged tissue. They help control blood flow and some muscle contractions.

Usually, women have periods every 25 to 35 days. The length of the menstrual cycle is counted from the first day of the period to the day before the next period.

A few days before a period, many women may show signs of PMS, or premenstrual syndrome. PMS is a combination of mood swings, cramps, and body changes, such as an increase in acne and bloating, due to large changes in hormone levels.

After a period starts, bleeding usually lasts for 3 to 7 days. In that time, it's common to lose 30 mL (1 ounce) of blood. That's about two tablespoons. Menstrual blood is from the inner lining of the uterus, so it's common for the blood to have clots and chunky bits in it. The flow of blood changes over time. Many periods start with light bleeding, but it's also not unusual for the first few days to be heavy. Women often report that the second day of their period has the heaviest flow. Because the uterus contracts to shed its inner lining, some cramping during a period is common.

While light cramping during a period is common, some people experience much worse pain during their periods. If the pain is so strong that it prevents you from doing your regular activities like going to school, there may be a problem. Very painful periods may be a sign of endometriosis. In endometriosis, the lining of the uterus grows outside of the uterus. When that happens, the hormonal changes signal for that lining to shed every menstrual cycle, so it swells and bleeds, but does not leave the body. That can cause a lot of pain.

Some people may not have periods at all or have them irregularly throughout the year. If you reached puberty, are not taking birth control, and do not have regular periods, this may be a cause for concern. Overexercising, undereating, and general stress may cause the body to stop periods altogether. Also, people with polycystic ovary syndrome (PCOS) may not get their periods regularly.

Other people have very heavy periods. An abnormally heavy period is when a person expels over 80mL of blood per cycle, which is more than 2 times higher than the usual amount. That may lead to anemia. Anemia is when the body doesn't have enough red blood cells to carry oxygen to all parts of the body. Fatigue is a common side effect of anemia.

Many abnormalities in the menstrual cycle may signal that something is wrong with the body. Some conditions may stop ovulation, while others may cause very painful cramps and other symptoms. The easiest way to tell if something is wrong is to track menstruation and related symptoms, as those are the only parts of the cycle we can see or feel.

• Hormones of the menstrual cycle
• Birth control and the menstrual cycle
• Polycystic ovary syndrome and the menstrual cycle
• Endometriosis and the menstrual cycle

Hormones of the menstrual cycle

The menstrual cycle is controlled by changing levels of hormones in the body. There are four main hormones related to the menstrual cycle. Those are estrogen, progesterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

The ovaries make most of the estrogen, but it is also made in the adrenal gland and fat cells. Estrogen rises slowly during the follicular phase, falls right before ovulation (shown as a yellow vertical bar), and has one more gradual rise and fall in the luteal phase.

The follicle cells that remain in the ovary after an egg is ovulated make progesterone. Progesterone stays low before ovulation. It then increases during the luteal phase and then falls at the end, which triggers menstruation.

The other two major hormones of the cycle are FSH and LH. The pituitary gland, which is a small, bean-shaped gland in the middle of the brain, makes both of these hormones.

LH is released right before ovulation, which triggers the release of an egg from an ovary. FSH levels rise at the end of the luteal phase and hit a small peak at the beginning of the follicular phase. This is what stimulates some of the follicles in the ovaries to grow (during the 'cyclic recruitment'). There's also a small FSH spike during ovulation.

Birth control and the menstrual cycle

Many types of birth control have an effect on the hormones of the menstrual cycle. Generally, they keep the level of certain hormones, like estrogen, steady over the cycle. This can prevent ovulation and may even stop periods from happening. They may also reduce symptoms of PMS that are caused by fluctuating hormones.

Some hormonal birth control methods, such as pills, cause periods to occur every 28 days exactly. That happens because those pill packages usually include a total of 28 pills, four to 7 of which are pills with no hormones. Those "sugar pills" cause an abrupt fall in levels of estrogen and progesterone, which triggers a period.

Some birth control methods keep hormone levels constant over the entire month. With those methods, there would be no drop in estrogen or progesterone, and periods would not occur.

Non-hormonal birth control does not stop ovulation. Instead, it may prevent fertilization in a few different ways. For example, condoms trap sperm cells and copper (non-hormonal) IUDs kill sperm cells and make it harder for them to reach the egg.

All hormonal birth controls, and a few non-hormonal types (like IUDs) may cause irregular bleeding and lots of pain in the first few months of use. These symptoms may lessen as the body gets used to the contraception. Some methods, like non-hormonal IUDs, may cause periods to be heavier and to last for a few extra days.

Polycystic ovary syndrome and the menstrual cycle

PCOS is an acronym for polycystic ovary syndrome. PCOS is a hormone disorder that causes increased levels of certain hormones in the female body, but it can cause a variety of other symptoms. Those often include cysts in ovaries and irregular menstrual cycles. PCOS affects 5-10% of women, but it is hard to diagnose, as it can be different for each patient. Scientists don't fully understand the causes of PCOS, but they do know that it comes with risks.

Many people with PCOS have a high resistance to insulin, which can lead to diabetes and can affect heart health. High insulin can also increase the androgens (like testosterone) in the ovaries. Androgens interfere with ovulation and may cause abnormal hair growth or balding.

Patients with PCOS often have bigger ovaries than those without PCOS. That's because in PCOS, small sacs called cysts start growing on the ovaries, which makes them larger. Those cysts may prevent ovulation, so many people with PCOS may struggle to become pregnant. Depending on the severity of PCOS, some people may still ovulate and be able to get pregnant. However, in most severe cases (as shown on the graph) no ovulation occurs. The lack of ovulation and the increase in insulin can greatly affect the hormonal cycle.

Increased insulin levels usually cause increased levels of luteinizing hormone (LH). But if there is no ovulation, there is no LH spike in the middle of the cycle. Estrogen levels can be normal or higher than normal. Levels of follicle-stimulating hormone (FSH) are low and do not vary much during the cycle. Progesterone levels are very low, as there is no corpus luteum to produce it if there is no ovulation.

While we don't know what causes PCOS, we know that exercise and a healthy diet are great ways to reduce the risk of having PCOS or the severity of its symptoms.

Endometriosis and the menstrual cycle

Endometriosis is a condition where the lining of the uterus grows on other parts of the body. The uterine lining is called the endometrium. It grows into a thick layer of tissue every menstrual cycle to prepare for pregnancy. If a pregnancy does not happen, that tissue is shed (or released) through the vagina. That process is called menstruation, or a period.

But what happens when that tissue is growing where it’s not supposed to? It sort of bleeds and sheds where it’s not supposed to. When this tissue bleeds outside of the uterus, it can be especially painful. Any of that blood and tissue outside of the uterus doesn’t connect to the vagina, which means it cannot leave the body. The tissue can grow and blood can pool in places where it shouldn’t. This often causes people with endometriosis a lot of pain during their periods. This pain can be so bad that it stops people with endometriosis from doing their usual activities while on their periods.

In people with endometriosis, extra tissue often grows on the fallopian tubes or the ovaries. When it grows here, it can affect someone’s ability to become pregnant. That’s because the tissue can make it more difficult, or even impossible, for sperm to find an egg. If endometriosis is severe, and affects fertility or everyday activities, a small surgery may be able to help. Surgeons can insert a small tool called a laparoscope into the abdomen through a very small cut. That tool allows them to see and remove the extra tissue, which may help relieve the symptoms of endometriosis.

Learn more about endometriosis in our story, Shedding Light on Endometriosis.