Once the menstrual cycle is established, post-puberty, it follows a basic pattern. While no two menstrual cycles are exactly the same, the basic hormone trends across the menstrual cycle look like this.
What are the stages of the menstrual cycle?
The menstrual cycle can be broken down into 4 stages, often considered in weeks (7 days) as the average cycle is 28 days long. Within each, different hormones are dominant and initiate and promote changes to the reproductive organs as well as the rest of the body.
Not every woman experiences these stages in neat 7-day blocks. Each stage can vary in length, which accounts for how NHS guidelines say a regular cycle can be anywhere between 23 and 35 days long and considered healthy. There are ways to track the different stages. Some women can tell where they are in their cycle because of certain symptoms showing up at different times, while others might use period trackers, like various apps, which may or may not include doing a daily temperature check, to pick up on the minute temperature changes that can occur around ovulation.
Week 1 and 2 of the cycle are known as the Follicular phase -the portion of the cycle that prepares the body for, and controls, the release of a mature egg -sometimes more than one. The end of the Follicular phase is ovulation.
Week 3 and 4 of the cycle are known as the Luteal phase. This stage begins around day 15, after ovulation, and ends at the beginning of menstruation. The Luteal phase supports eggs for possible fertilisation, and tells the body what to do if this does, or does not, occur.
What is happening in each stage?
The Follicular phase begins at menstruation and lasts until ovulation. This phase can be anywhere from 14-21 days long. It involves the last stages of maturation of (typically) a single egg (oocyte) within an ovary up until this egg is released into the Fallopian Tube. The maturation of an egg actually takes far longer than 14 days, and begins weeks before that particular egg will be released, and is called folliculogenesis.
What are the basics of egg maturation?
The goal of folliculogenesis is to produce a primary egg, from a group of growing follicles. Follicles, also called oocytes, or as called above ‘eggs’, and mature in large groups (as high as 1000 at a time), from which this single follicle/egg will emerge. This seems like a very large number of eggs, but a foetus actually develops anywhere from 4-6 million of these follicles during the 6-9 month mark of pregnancy. By birth, this number is suggested to be closer to 1-2 million. Each month, up until puberty, groups of eggs will start to mature within the ovaries, however, lacking specific sex hormones, will not be able to mature fully and ultimately be broken down. This can happen to up to 10,000 eggs each month pre-puberty. During puberty, when sexual hormones rise and start to support a menstrual cycle, eggs can begin to mature fully. A typical egg reserve of around 300-400 thousand eggs remains by this point. Each month, a pool of eggs (around 1000 follicles) will undergo the stages of maturation, leading to one primary mature egg being released. Sometimes there is more than one fully matured egg and this can lead to multiple eggs being released that month. All ‘unchosen’ eggs will be broken down.
This process begins as soon as the last cycle ends, which is why menstruation week is considered to be week 1, and not week 4, because it marks the beginning of a new cycle. The menstrual cycle, simplistically, is a process of building, breaking down, and removing cells, month on month.
So what is happening within each ‘week’ of the follicular phase?
Week 1 - Bleed
Menstruation (also called menses, or period) is the name for the release of blood and other tissue from the lining of the uterus, which has been building up in preparation to house a fertilised egg. This typically lasts between 2 and 7 days, with heavier bleeding often within the first couple of days, followed by lighter discharge, until completed. The heaviness of a period, and the length of bleeding, is influenced by hormonal levels, but also diet and lifestyle factors. This can include how hydrated someone is, or if they have enough iron in their blood.
The colour of discharge during this time can vary -from bright red, to darker reds and browns, or pink at the onset when less blood is being released along with other cells. The colour and consistency of the discharge, e.g. whether it contains clots or other tissues, can potentially be signs of hormone imbalance or poor menstrual health. Any extreme period symptoms, like heavy bleeding and extreme pain should always be evaluated by your health care practitioner.
As mentioned above, the ovaries are preparing for the next egg release already. Follicle Stimulating Hormone (FSH) is released from the pituitary gland in the brain, and ‘oversees’ folliculogenesis. Its ‘sister’ hormone Lutenising hormone (LH) is also present throughout the next 2 weeks, also secreted from the pituitary, gradually rising throughout the follicular phase and working alongside FSH to oversee ovarian functions. Importantly, LH stimulates the production of oestrogen within the ovaries.
Week 2 - Build
Week 2 is where re-building begins. The womb needs to be as hospitable as possible to the egg when it is released at ovulation. The uterine lining needs to be ready and able to accept a fertilised egg, and so post-period, the process of building up the uterine lining begins again.
Oestrogen, released from the ovaries, promotes this new round of preparing the womb for possible fertilisation and implantation. As oestrogen is released, FHS is forced into decline, and oestrogen continues to rise. This increase in oestrogen promotes the thickening of the uterine lining (endometrium) within the womb. It is also linked to many other symptoms around ovulation, including the rest of the body, like thinning of cervical mucus (to aid fertilisation), but also things like changes in physical appearance, like skin. Lutinising hormone (LH), which has also continued to rise, joins oestrogen in supporting the build up of the endometrial lining.
Oestrogen hits its peak a few days before ovulation around day 14, and starts to decline, replaced as ‘top hormone’ by the increasing LH, which will increase rapidly to also reach its peak just before ovulation. It is this sudden rise in LH, that causes the rupture of the ovarian follicle, and releases the egg. Ovulation marks the end of the follicular phase.
The Luteal phase covers the second half of the cycle, bookended by ovulation and menstruation.The typical luteal phase, as demonstrated in these infographics/images, cover what happens with the different hormones when pregnancy is not the outcome, and the cycle begins again. If pregnancy does occur, hormones remain at higher levels to support the continued growth of the zygote. The luteal phase can be, again, broken roughly into 2 stages -sometimes called mid- and late-luteal stages, and each roughly last a week, collectively anywhere between 12 and 17 days long.
So what is happening within each ‘week’ of the luteal phase?
Week 3 - Sustain
The Luteal phase begins the day after ovulation. It is effectively the point in time where the womb is supposedly primed to receive a fertilised egg. The ‘fertile window’ is actually fairly short. It begins just before ovulation (in the follicular phase), and lasts a couple of days post ovulation. This isn’t to say that pregnancy can’t occur during other parts of the menstrual cycle, especially if cycles are irregular and mapping them out is difficult. In fact fertilisation can even occur during a period. But the textbooks say that this window of fertility is around 3 days prior to ovulating and extends to only around a day after ovulation. The main hormone at this stage is still Lutenising hormone (LH). This hormone now slows the growth of the endometrial lining, and prepares the endometrial lining for implantation. It also stimulates the ovarian follicle (from which the egg was released), now called the Corpus Luteum, to produce progesterone. If implantation occurs, both LH and progesterone will support early pregnancy and pregnancy maintenance. A few days after ovulation, progesterone takes over as the primary hormone, LH continues to drop and oestrogen remains low. Progesterone continues to promote thickening of the endometrial lining to support implantation as much as possible.
If an egg is fertilised by a sperm cell, it will travel from the fallopian tube (where it still is), down into the uterus, all the while dividing in cells and growing. Implantation of the now-zygote can take anywhere between 6 and 12 days to occur. At this point progesterone is the main hormone present, and continues to rise into the later stage of the luteal phase.
4 - Renew
If this implantation does not occur, the body will start to reset the system to begin again. Progesterone continues to rise but has a far less sharp peak than oestrogen and LH, and rounds out around day 21 and into decline. This decline is caused by the breakdown of the Corpus luteum, which was producing it, and therefore reducing available progesterone. Progesterone is no longer there to maintain the uterine lining, so the process of shedding this lining starts.
The Luteal phase usually lasts around 14-16 days. A short luteal phase might occur if the body doesn’t produce enough progesterone. This could be because of hormonal disorders like PolyCystic Ovarian Syndrome (PCOS), thyroid disorders, very low body weight, obesity, extreme exercise, and stress. Signals of low progesterone could be an overall shortening of the cycle, increased irregularity of periods, digestive symptoms (eg. bloating), changes in weight, mood irregularities, and issues with sleep, among others.
It is during this last stage of the cycle that many people experience symptoms associated with premenstrual syndrome (PMS), outlined below.
What symptoms are common during the menstrual cycle?
Throughout the month
The above pattern of hormones is a lot less regulated than that explanation would have us believe. Were all hormones to peak and dip where ‘meant to’, with the perfect length of each stage, the menstrual cycle could, in theory, come with few symptoms. But life isn’t like that, and a myriad of internal and external factors influence the menstrual cycle of individuals in so many ways, that there are millions of examples of what a menstrual cycle looks like. There are common co-occurring symptoms that we are only just realising relate to the menstrual cycle, and are getting research focus now, and likely more to be discovered.
Individuals using hormonal contraceptive devices can experience a completely different cycle than that of those not using medical interventions, as can those with recognised hormonal conditions, chromosomal disorders, genetic variants, as well as good old fashioned stress.
Some people can tell when they have ovulated. High oestrogen levels promote small changes around the body which can sometimes be perceived, like changes in the appearance of the skin. More specific signs that demonstrate ovulation has occurred, or is about to, will typically appear a few days before and continue into a few days post ovulation.
- Clear, mucus discharge -commonly described as egg-white in consistency
- A slight up-shift in temperature, which can be picked up using a sensitive thermometer, like a basal body thermometer.
- Similar to premenstrual symptoms -breast tenderness, bloating
Premenstrual syndrome (PMS) is a collection of symptoms that can appear in the later portion of the luteal stage, typically a few days before bleeding begins. There are around 150 recognised symptoms that are considered part of PMS, both physiological and psychological. Typical symptoms can include:
Changes to sleep, mood, and brain function, including: increased feelings of depression and anxiety, and general emotions; insomnia and changes to sleep patterns; cognitive changes like brain fog, poorer focus and concentration
Digestive changes, like bloating, cravings, constipation; Sensitivity in reproductive tissues, eg breast tenderness, and increased sensitivity to pain in general; changes to skin, possible acne breakouts; Muscle aches and pains; increased tiredness and fatigue; and water retention, eg. oedema in extremities (hand, feet, ankles).
PMS apparently affects between 30-40%, with anywhere between 3 and 10% of these describing their symptoms as severe enough to ‘impact on their lives’. However, that number seems very low given that PMS can be experienced at any age, at any point of reproductive life, when sex hormones are constantly influenced by internal and external stressors. There is yet no clear understanding of the mechanisms behind PMS, except to say that it is recognised to involve more than just sex hormones. Research suggests that PMS, and other menstrual syndromes, are caused by interactions between sex hormones and neurotransmitters (eg. serotonin), and influenced by genetics and social context. As sex hormones interact with many areas of the body, these hormones, eg Oestrogen, can influence neurotransmitters in the brain, and PMS could be the emotional and physical manifestations of this.
When PMS symptoms involve changes to mental health, like anxiety and depression, or extreme mood swings, PMS might be reclassified as premenstrual dysphoric disorder (PMDD).
Any symptoms that are severe, like changes to mental health, pain, ongoing digestive issues etc, should always be discussed with a health professional to rule out any other causes, before written up as PMS or PMDD.
During a Period
Periods can be very different person to person. Symptoms will be influenced by internal and external factors, such as stress, physical exertion, medications, diet, etc. Some months can appear relatively symptom free, while others carry far more with them.
A number of symptoms are considered normal to experience throughout a period. Cramping of the uterus is common, brought on by the secretion of prostaglandin by the uterus, which creates contractions and aids in the shedding of the uterine lining. Cramping can begin before blood appears, and can cause various degrees of pain -mild to severe, felt within the uterus but also potentially throughout the abdomen, back and even legs. Cramping can also impact bowel movements, as prostaglandin also influences digestive movement. While sometimes period pains can be managed with over the counter medications, severe pain, which impacts someone’s ability to carry out regular activities and live as they wish, should always be investigated by a health professional, as it could be a sign of reproductive or hormonal conditions, such as Endometriosis.
What can I do to help with period symptoms?
During this stage, women often develop a number of activities or mechanisms to help with period symptoms. Having heat packs or hot water bottles against the abdomen can help ease cramps. There are electrical devices and botanical patches that are designed to help reduce pain when attached to the skin of the abdomen. Certain exercises, resting, nourishing foods, and certain supplements may also be a part of monthly actions to support a happy period. There are many sources of information on menstruation that encourage ‘living life as normal’ during a period, that periods ‘don’t have to hold you back!’, but the reality is many benefit from resting during this week. Ultimately, it is a personal experience, embraced as one chooses to -which could include choosing not have a regular period at all, eg. when using the oral contraceptive pill.
For more information of contraceptive devices, click here: https://www.nhs.uk/conditions/contraception/