The main points
- The menstrual cycle occurs because of a complex relationship between hormones from the brain and ovaries.
- The purpose of the menstrual cycle is to prepare the body for a possible pregnancy.
- When pregnancy does not occur, a menstrual bleed happens. This bleeding is called a menstrual period or menstruation.
- Each person’s experience of the menstrual cycle is different, with variations in cycle length, bleeding and symptoms.
- Some people experience menstrual cycle concerns such as heavy or painful periods and premenstrual syndrome (PMS). There are lifestyle modifications and treatment options for these.
The menstrual cycle – overview
The menstrual cycle is a natural recurring cycle of changes in the ovaries, lining of the uterus (endometrium) and sex organs. The purpose of the menstrual cycle is to prepare the body for a possible pregnancy.
During the menstrual cycle, a mature egg is produced by the ovaries and the lining of the uterus thickens to support a possible pregnancy. When pregnancy does not occur, the egg and lining of the uterus are shed from the vagina during a menstrual bleed. This bleeding is called a menstrual period or menstruation.
The first menstrual bleed or period (called menarche) usually occurs between the ages of 12 – 14 years but can occur anytime between the ages of 9 – 15. Before a period starts, other sex characteristics have usually developed, such as pubic hair and budding breasts.
The last menstrual bleed or period usually occurs between the ages of 45 – 55. This is known as menopause.
Each person’s experience of the menstrual cycle is different, with variations in cycle length, bleeding and symptoms.
Menstrual cycle length
The length of the menstrual cycle is calculated from the first day of bleeding (day one) to the first day of the next bleed. The average length of the menstrual cycle is 28 days, but this can vary between 21 – 35 days. The length of the menstrual cycle varies between people and from one cycle to the next.
Menstrual bleeding (menstrual period or menstruation)
Menstrual bleeding is the elimination of the egg and thickened lining of the uterus (endometrium) from the body through the vagina. Menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells) and mucus.
Menstrual bleeding can vary in the number of days, amount, flow and colour. It can also vary between each menstrual cycle and at different life stages.
Bleeding usually lasts between 3 – 7 days, and most people lose less than 80ml of blood (about one-third of a cup) in total. Menstrual flow is usually heavier for the first days and becomes lighter. The colour of the blood will change depending on flow, from dark or bright red to dark or light brown. It is normal to see small clots in menstrual blood.
To manage and absorb bleeding you can use products like pads (sanitary pads or napkins), tampons, a menstrual cup or period underwear. It is good to be prepared for menstrual bleeding and keep these products handy. Pads, tampons, menstrual cups and period underwear come in different shapes and sizes but all of them need to be changed every four to six hours to stop leakage and in some cases prevent infection. You can talk to a trusted friend, adult or health professional for more information on how to use these products and where to purchase them.
Most people experience symptoms in the days leading up to their menstrual period. These are referred to as premenstrual symptoms and occur due to fluctuations in the sex hormones, oestrogen and progesterone, and the brain chemical, serotonin.
Symptoms vary between people and can also vary between each menstrual cycle. For most people symptoms are mild and manageable.
The most common symptoms include:
- irritability, anxiety, depression, mood swings, sadness, anger
- difficulty concentrating
- changes in sleep
- tiredness, lethargy
- abdominal bloating
- fluid retention
- changes in appetite, overeating or specific food cravings
- constipation and/or diarrhoea
- vaginal odour (smell)
- weight gain
- skin changes
- breast swelling, tenderness and/or pain
- headaches and/or migraines
- slight spotting and/or pain at the time of ovulation.
- Hormones and the menstrual cycle
The menstrual cycle occurs because of a complex relationship between hormones from the brain and ovaries. The pituitary gland (in the brain) produces luteinizing hormone and follicle-stimulating hormone. These hormones promote ovulation (release of an egg from the ovary) and stimulate the ovaries to produce oestrogen and progesterone (sex hormones). Oestrogen and progesterone stimulate the uterus (and breasts) to prepare for possible fertilisation and pregnancy.
The menstrual cycle is a biofeedback system, which means each structure and gland is affected by the activity of the others.
Phases of the menstrual cycle
The phases of the menstrual cycle are:
The follicular phase starts on the first day of menstruation and ends with ovulation. On average it lasts around 13 – 14 days.
When the follicular phase begins, the lining of the uterus is thick. If an egg has not been fertilised, lowering levels of oestrogen and progesterone result in menstruation (a period).
During menstruation the pituitary gland increases production of follicle stimulating hormone, stimulating the growth of around 5 - 20 follicles in the ovary. Each follicle contains an immature egg. Over approximately 10 days, one of these follicles (the dominant follicle) will mature into an egg, while the others break down. The maturing follicle produces oestrogen, which stimulates the lining of the uterus to thicken in preparation for possible pregnancy.
The ovulatory phase begins with a surge in luteinizing hormone (and to a lesser degree follicle-stimulating hormone) and ends when the egg is released. The ovulatory phase usually lasts 16 – 32 hours.
The surge in luteinizing hormone stimulates the mature egg to rupture from the ovary. This process is called ovulation. During the surge in luteinizing hormone, the oestrogen level decreases and the progesterone level starts to increase.
The ruptured egg is funnelled into the fallopian tube and towards the uterus by waves of small, hair-like projections.
The luteal phase begins after ovulation. It lasts about 14 days (unless fertilisation occurs) and ends just before the next menstrual period.
During the luteal phase, luteinizing hormone and follicle-stimulating hormone levels decrease. The ruptured follicle (left on the ovary after ovulation) forms a structure called the corpus luteum. The corpus luteum produces progesterone and a small amount of oestrogen. This combination of hormones causes further thickening of the lining of the uterus, to prepare for possible implantation.
From the time of ovulation, the life span of an egg is around 24 hours. For pregnancy to occur the egg must be fertilised by a sperm in this time. If it is not fertilised within 24 hours, pregnancy is not possible. Fertilisation is more likely when sperm are present in the reproductive tract before the egg is released. Most pregnancies occur when sex has occurred in the couple of days before ovulation.
If a fertilised egg (embryo) implants in the lining of the uterus, it begins to produce a hormone called human chorionic gonadotropin (hCG). This hormone maintains the corpus luteum, which continues to produce progesterone, until the growing foetus can produce its own hormones.
If pregnancy does not occur, the corpus luteum degenerates and levels of progesterone and oestrogen decrease and a new menstrual cycle begins.
Common menstrual problems
Some of the more common menstrual problems include:
- Amenorrhoea: absence of menstrual bleeding/periods (no menstrual periods).
- Pre-menstrual Syndrome: a combination of symptoms in the days leading up to menstrual bleeding/periods.
- Dysmenorrhoea: menstrual period pain.
- Menorrhagia: heavy menstrual bleeding/periods.
It is recommended you see a health professional if you are experiencing menstrual cycle changes or symptoms of concern, including pain and/or bleeding after sex or in between menstrual periods.
There are many lifestyle modifications and treatment options to manage, reduce or stop menstrual cycle conditions. Your health professional will discuss options with you.
Where to get more information, support or advice
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