Menstrual health glossary

This article was medically reviewed by Andrew Horne, Professor of Gynaecology and Reproductive Sciences at Edinburgh University's MRC Centre for Reproductive Health.

During our research and focus groups we spoke to a number of people living with endometriosis who said that when they were first diagnosed, they found all the terminology and definitions confusing. They also highlighted a lack of simple resources to help them understand some of the terms they were hearing from doctors or reading online. 

We worked with our clinical research team and Professor Andrew Horne, Professor of Gynaecology and Reproductive Sciences at The University of Edinburgh and one of the leading specialists in endometriosis in the UK, to create a list of some of the terminology you might hear, along with definitions. 

• AFAB – an individual who is Assigned Female at Birth (AFAB). This is based on their external sex genitals at birth. AFAB does not describe a person’s gender identity.  
• Menarche – the first menstrual period in women and people assigned female at birth. On average, people experience this at age 12-13, but it is also normal to get your first period between the ages of 10 and 16.  
• Menstrual cycle – It is not only the period. It is the whole chain of activities that involves the brain, uterus, and ovaries that are all controlled by hormone changes. It is not always predictable or precise, and can change depending on things like age, stress, exercise, weight fluctuations, or medication. It starts on the first day of your period and ends the day before the next period. This is on average 21-35 days, but can vary between individuals. Menstrual cycles happen in women and AFAB. There are four phases (or stages) of the menstrual cycle: menstruation, follicular, ovulation, and luteal.  
• Menstruation –  

What is menstruation? also known as a period, or menses. This is the first phase of the menstrual cycle. It is the monthly shedding of the uterus lining, called the endometrium. The length can vary between individuals but on average is 4-6 days.   

What is happening with hormones? Estrogen and progesterone are at their lowest, which helps the endometrium break down.

When does menstruation happen? The first day of menstruation is considered day 1 of the menstrual cycle.  

• Follicular phase–  

What is the follicular phase? also known as proliferative phase. This is the longest phase of the menstrual cycle. Here, the ovaries produce many small fluid-containing sacs called follicles until one becomes the most mature. 

What is happening with hormones? Estrogen levels rise which signals the endometrium to thicken and provide a space for the egg to implant.  

When does the follicular phase happen? Since menstruation is included in the follicular phase, this stage is the longest and can lasts around 14 days.  

• Ovulation –  

What is ovulation? The most mature follicle is released from the ovary. The follicle bursts, releasing the egg. The egg leaves the ovary and enters the fallopian tube to prepare for fertilization. 

What is happening with hormones? Estrogen levels are very high. When it reaches its peak, it causes another hormone LH to rise. This is what releases the egg from the follicle.  

When does ovulation happen? This happens on one day each month usually around the middle of the menstrual cycle. It typically occurs about 14 days before the next period starts.  

• Luteal phase - 

What is the luteal phase? also known as secretory phase. The leftover follicle releases estrogen and progesterone to help the endometrium thicken. This is done to prepare for pregnancy, giving the egg a platform to implant into.  

What is happening with hormones? If pregnancy happens, progesterone stays high to maintain a thick endometrium. If pregnancy does not happen, the follicle degenerates, which causes a drop in progesterone and the endometrium breaks down. Then, menstruation happens and the cycle restarts.  

When does the luteal phase happen? On average, the luteal phase lasts around 14 days. It is considered short if it lasts less than 10 days. If this happens, the endometrium does not have enough time to thicken, so people may experience more difficulties getting pregnant in this case.  

• Menopause –When you go through 12 consecutive months with no period (menstruation), you are considered to be in menopause. On average, this starts around ages 45 to 55. After menopause, women and AFAB will permanently stop having a period since their ovaries stop producing hormones. Menopause symptoms can last for 7 – 9 years on average but can go on for over 10 years.  These individuals can still experience menstrual health conditions like endometriosis, fibroids, and PCOS even after menopause.  
• Uterus – Also known as the womb. It is the hollow organ located in the pelvis of women and AFAB. It responds to hormones and is responsible for many functions including menstruation, pregnancy, and childbirth. In the first stages of pregnancy, the embryo implants in the uterus. The uterus has three layers: endometrium (outer layer), myometrium (middle muscle layer) and perimetrium (bottom layer).  
• Vagina – The muscular tube between the cervix and the vulva. The opening is where menstrual blood leaves the body during the period, and where babies exit during childbirth. It can also be used for insertion, such as for sexual intercourse, tampons, or menstrual cups. People often use the term vagina to refer to the external genitalia anatomy, but this is actually the vulva. The vulva includes the labia minora and majora, opening of urethra and vagina, clitoris, and other tissue.  
• Ovaries – Two glands attached to the end of the fallopian tubes that are responsible for producing eggs. The hormones oestrogen and progesterone are produced here. Some testosterone is also made in ovaries.  
• Fallopian tube – Two long tubes that connect the ovaries to the uterus. During ovulation, an egg passes from the ovary into the fallopian tube, where it can get fertilized by a sperm cell.  
• Cervix – Connects the uterus to the vagina. It opens slightly to allow the passage of menstrual blood or sperm cells. During pregnancy, it stays tightly closed to prevent the baby from exiting until labor contractions start.  
• Follicle – Small sacs filled with hormones and fluid that grows during the follicular phase. When they are growing, they contain an immature egg called an oocyte. During ovulation, high amounts of hormone cause the most mature follicle to open and release the oocyte. This mature oocyte is now called an egg.  
• Egg – Also known as ovum. If the egg gets fertilized by a sperm cell, it will be called a zygote. If the egg does not get fertilized, it will still be an egg.  
• Bowel – Also known as intestines. It consists of the small and large intestine and is responsible for breaking down food to collect nutrients and passing waste to the rectum.  
• Rectum – The organ at the end of the intestine that functions to store poo.  

• Hormones – chemicals secreted by organs that act as messengers to communicate to other organs of the body. There are several classes of hormones, one is the steroid group. These hormones are made from cholesterol, and can be transformed into oestrogen, progesterone, or testosterone.  
• Oestrogen – a major steroid hormone released by both male and female sex organs, but females produce more of it. Before menopause, oestrogen is mainly released from the ovaries. After menopause, it is mainly released by the adrenal glands and fat tissue. In pregnancy, it is mainly released by the placenta. When the follicles grow in the ovaries during the follicular phase, they secrete oestrogen. This thickens the endometrial lining to prepare for implantation of a zygote. Many conditions are related to high oestrogen levels, such as PMDD, breast cancer, ovarian cancer, endometriosis, endometrial cancer, and PCOS.  
• Progesterone – during the luteal phase, the leftover follicle produces high amounts of progesterone. Its main function is to maintain a thick endometrial lining during the early stages of pregnancy. Other non-reproductive roles for progesterone include regulating mood, inflammation, thought processes, and sexual libido. During the menstruation and follicular phase, progesterone levels are typically low. Oestrogen and progesterone work in balance to make sure the endometrial lining does not get too thick.  
• LH – luteinizing Hormone (LH) is produced by the pituitary gland of the brain. LH levels are controlled by GnRH, another hormone secreted by the hypothalamus of the brain. LH stimulates the ovaries to produce oestrogen during the follicular phase and progesterone during the luteal phase. When oestrogen is at its highest, it will cause LH to peak, triggering ovulation.   
• FSH – Follicle Stimulating Hormone (FSH) is also produced by the pituitary gland of the brain and is under the control of GnRH. As FSH rises during the follicular phase, the follicles start to grow and release oestrogen. Since only one follicle can mature into an egg, oestrogen restricts FSH. The drop in FSH causes the smaller, premature follicles to die off since they are starved of FSH. This allows one follicle to be released at ovulation. FSH levels are higher in the follicular phase and are lower during luteal phase. Normally LH to FSH levels are found at similar amounts in the blood. ? 
• GnRH – Gonadotropin-releasing hormone (GnRH) is released from the hypothalamus of the brain. They travel to the pituitary gland and control the levels of LH and FSH. In males, this results in the production of testosterone. In women and AFAB, this results in the production of oestrogen and progesterone. GnRH levels are controlled by a communication loop between the ovaries and the brain. When the levels of steroid hormones are too high, estrogen and progesterone will communicate to the brain to produce less GnRH, and vice versa.  

• Metrorrhagia – bleeding outside the usual time of period. 
• Menorrhagia – now known as ‘heavy menstrual bleeding’ (HMB). This heavy bleeding occurs during the expected time of period but lasts longer, typically more than seven days.  
• Amenorrhea – absence of a period. 
• Oligomenorrhea – having your period infrequently, meaning it does not come every month. Medically, this is fewer than six to eight periods a year.  
• Hypomenorrhea – very little bleeding during period, where periods last around two days. 
• PMS – Premenstrual Syndrome (PMS) are a series of symptoms that occur after ovulation, during the luteal phase of the menstrual cycle. They include appetite, psychological, behavioral, and physical symptoms. People with PMS do not have abnormal hormones, but rather are more sensitive to the changes in hormone levels, such as when oestrogen drops during the luteal phase and progesterone rises.  
• PMDD – Premenstrual Dysphoric Disorder (PMDD) is a severe form of PMS. It is a chronic condition where people are hypersensitive to the hormone changes that occur during the luteal phase. Hormone fluctuations can cause a deficiency in serotonin, which is often called the ‘’mood’’ neurotransmitter. The symptoms are similar to PMS but are much more intense, negatively affecting daily activities and quality of life. 
• Endometriosis – a condition where tissue, similar to the lining of the uterus (known as the endometrium) grows outside the uterus. Once considered a pelvis-only disease, it has since been found growing in every organ of the body. However, where it appears and to what degree is different for everyone. Endometriosis affects women and AFAB.  
• Endometriosis stages – Endometriosis can be classified into four stages. These stages are based on location, extent and depth of the endometrial-like tissue/lesions and the presence and severity of adhesions (scarring). It is important to be aware that having a more advanced stage of endometriosis does not always mean you will have more severe symptoms or pain. Endometriosis doesn’t always go from one stage to the next and if left untreated it can stay at the same stage over time or it can progress: 
• Stage one – ‘Minimal’, few superficial lesions may be found on your organs or the tissue lining your pelvis or abdomen. Mild adhesions present. Little or no scar tissue.  
• Stage two – ‘Mild’. Endometrial tissue is more widespread than in stage one, with some deeper lesions present. There may be some scar tissue.  
• Stage three – ‘Moderate’. Endometriosis is more widespread than stage 2. While there can be superficial lesions, there are much more deep endometrial lesions present, often involving the ovaries (cysts or endometriomas). Scar tissue can be much denser.   
• Stage four – ‘Severe’. Most widespread with many deep endometrial lesions and dense adhesion. There can be large cysts found on one or more ovaries. 
• Fibroids – Also known as uterine myomas or leiomyomas. They are non-cancerous growths that develop in or on the uterus. They are made of muscle tissue similar to the uterus muscle. Some people are asymptomatic, but typical symptoms can include heavy periods, non-menstrual abdominal pain, lower back pain, frequent need to urinate, constipation, or pain during sex.  
• PCOS – Polycystic Ovarian Syndrome (PCOS) occurs when the ovaries produce an abnormally high amount of male steroid hormones called androgens. This causes the ovary to make multiple immature follicles (cysts) instead of one mature follicle. As a result, these follicles do not release eggs so the individual does not ovulate. People who have PCOS have a high chance of experiencing infertility but can receive hormone treatment to help with pregnancy. People with PCOS have high oestrogen levels which causes high LH. The imbalance between LH and FSH is what prevents successful ovulation.   
• Adenomyosis – A condition where tissue similar to that of the endometrium grows into the muscle wall of the uterus. Its symptoms overlap with endometriosis, so it can be difficult to diagnose.   

• Adhesions – bands of scar tissue that can join organs together. Adhesions form when lesions stick together. Repeated surgeries can also cause a build-up of scar tissue, creating new sites where lesions can grow, making endometriosis symptoms worse.
• Lesions – patches of endometrial-like tissue found growing outside of the uterus. They can be found in other organs outside of the pelvis such as the gastrointestinal tract, lungs, and abdomen but this is considered rare. There are three types of endometriosis lesions. Lesions also vary by size, color and location. 
• Superficial peritoneal endometriosis – found mainly on the pelvic wall lining. 
• Endometrioma – cysts most commonly found in the ovaries. They are filled with old menstrual blood which creates a brown color, which is why they are referred to as “chocolate cysts”. The presence of these indicates a more severe stage of endometriosis. 
• Deep endometriosis – previously known as deep infiltrating endometriosis (DIE). This is characterized by complex lesions found very deep in the tissue. It can occur in organs near the uterus including the recto-vaginal septum, bladder and bowel. It can also be found in other organs outside of the pelvis such as the gastrointestinal tract, lungs, and abdomen but this is considered rare. 
• Menstrual effluent –scientific terminology for fluid that flows from the uterus as part of the menstrual cycle. It is typically referred to as menstrual blood, however it does not only consist of blood. Menstrual effluent is composed of blood, vaginal fluids and tissue.  

• Ultrasonography – an imaging method that uses sound waves to produce images of structures within your body. It can be used as part of the diagnosis process for endometriosis. Negative results don’t rule out endometriosis as superficial endometriosis lesions cannot be detected by this method. 
• Magnetic resonance imaging (MRI) – an imagine technique doctors may use to help diagnose endometriosis. It can be particularly helpful for those with deep endometriosis. 
• Laparoscopy – see below. It is used for both diagnosis and treatment.   

• Hormone treatment – prescribed to stop or limit the production of oestrogen in the body which can reduce the endometriosis tissue and help manage the pain. This includes combined oral contraceptive pill (COC), progestins (or progestogens), and GnRH analogues. Symptoms will re-emerge when the treatment is stopped.  
• Combined oral contraceptive pill - contains the hormones oestrogen and progestogen. It is prescribed for endometriosis as it can help relieve the associated symptoms. It can help make periods lighter and less painful. Symptoms will re-emerge when the treatment is stopped.  
• Progestogens – these can be given through an IUS (intrauterine system) which is placed in the womb and releases the hormone, via a contraceptive injection and implant as well as in tablet form (such as the progestogen-only pill). Progestogens, or synthetic compounds similar to progesterone called progestin, can also help make periods lighter and less painful.  
• GnRH-analogues - synthetic hormones that cause a temporary menopause, which reduces the production of oestrogen. Typically given as an injection and can either be a one off or as a course, for example over 6 months (or longer).  They are sometimes prescribed after surgery to reduce the recurrence of endometriosis. They are prescribed with add back hormone replacement therapy to minimize their side effects (usually a once daily tablet). 
• Laparoscopy – a ‘minimally invasive’ surgical procedure that allows a specialist gynaecological surgeon to examine the inside of the abdomen and pelvis under a general anaesthetic. A small tube called a laparoscope is inserted into the tummy with a video camera on it, which returns images to a monitor. It is used to identify the presence of endometriosis and also remove endometriosis tissue. It is carried out under general anesthetic. In order to remove the tissue, thin tools are used to either apply heat, a laser or a beam of gas to the tissue to destroy or cut out the endometriosis lesions.   
• Ablation – a technique that uses a heat source to destroy the endometriosis tissue at a surface level. This will not remove the underlying or deep part of the lesion.  
• Excision – removal of the endometriosis tissue by cutting it out completely. Some randomized clinical trials have shown similar effectiveness for treating pain using both excision and ablation, however other studies show more relief using excision. Larger follow-up trials are required in the future to confirm these findings, so your doctor will decide based on an individual basis.   
• Hysterectomy – removal of the womb. A major operation that will have a significant impact and is only recommended if other treatments and surgery haven’t worked and the patient knows they won’t want to get pregnant. It cannot be reversed. It also isn’t a guaranteed method of fully removing endometriosis as you can still experience symptoms afterwards.  

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