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Menstrual Cycle and Pregnancy

The menstrual cycle refers to the changes that the bodies of women and people with uteruses go through that enables pregnancy to happen. Each cycle lasts around 28 days and has four main phases.

This page is about the reproductive system of women and people with a uterus (womb). It talks about the reproductive system, the menstrual cycle, periods and how pregnancy happens. Information about the reproductive system of men and people with penises. 

What is the menstrual cycle? 

You might have heard about the menstrual cycle, or menstruation, in relation to having periods, but there is so much more to know!  

The menstrual cycle, sometimes known as the fertility cycle, is the series of natural changes that happen in the reproductive systems of women and people with a uterus. It is what makes pregnancy and having babies possible. 

The menstrual cycle usually lasts between 21 – 35 days, most commonly 28 days, but it can be shorter or longer and for some people the length will vary each time. 

Did you know…?
The word menstruation comes from the Latin word ‘mensis’, which means month, and the Greek word ‘mene’, which refers to the moon.  
In ancient times, people thought that the menstrual cycle was related to the moon’s cycle because both last around 29 days (it’s not – that was just a coincidence!). 

The menstrual cycle is controlled by hormones and the changes to these hormones in the different phases of the cycle can affect someone’s mood, energy, feelings and libido (sex drive); though some people don’t notice any changes between the different phases.  

This is why it’s a great idea to understand your cycle more so you can prepare for the different changes it brings to your body and your feelings.

The Reproductive System 

To understand the menstrual cycle, it’s helpful to understand the reproductive system of women and people with a uterus. 

Every human has a reproductive system which is made up of sex characteristics such as genitals (the penis and the vagina and vulva), sex hormones and internal organs. These parts work together to make pregnancy happen. 

Parts of the reproductive system

Reproductive system. In the centre is the uterus whicha at the top has two arms coming out of tit, these are the fallopian tubes and on the end of these are circular sacs which are the ovaries. The uterus, womb in the centre leads down into the vagina. Where the vagina and uterus meet is the cervix
  • The Vulva = We often refer to the external genital organs (the bits you can see) as the vagina, but this is actually called the vulva. Some parts of the vulva that you might have heard of are the inner and outer labia (sometimes known as ‘lips’), the mons pubis (where pubic hair often grows) and the clitoris.  Find out more about your vulva
  • The Uterus = This is the part of the body where a baby grows during pregnancy. It is normally about the size of a fist but grows with pregnancy as the baby does. The uterus is often called the ‘womb’. 
  • The Cervix = The cervix can be found at the top of the vagina and is the entrance to the uterus. Your cervix changes position as you go through the menstrual cycle and can feel harder closer to your period and softer around the time of ovulation.  
  • The Vagina = The vagina is the muscular tube inside the body that leads from the cervix (the opening of the womb) to the vulva. This is where you bleed from during your period.  
  • The Fallopian Tubes = There are two fallopian tubes that link the ovaries to the uterus. These are the tubes which an egg will pass through and where sperm will meet the egg ending in pregnancy.  
  • The Ovaries = There are two ovaries which are linked to the uterus by the fallopian tubes. The ovaries are almond-shaped glands that produce hormones and eggs which they store until ovulation.  Fun fact: A woman/person with a uterus is born with a lifetimes supply of eggs – normally around 1-2 million!  

What is intersex?
Some people’s reproductive system does not include all of these parts, for example some people with a uterus might not have a vulva, and some people with a vulva might not have a uterus. This is known as intersex.

The phases of the menstrual cycle

You can explore each of these phases and how they might affect your body and mood below. How you feel and what you feel like doing in each phase is specific to you. We’ve included some suggestions of how you may feel and want to spend your time but it’s important you listen to your own body.  

Days 1-5: The Menstrual Phase (Bleeding)


Low levels of oestrogen and progesterone, rising levels of follicle stimulating hormone (FSH)

Discharge and vaginal mucus

May be slightly brown or pink before your period and towards the end. 


Energy at its lowest, less social, need more rest

Time for

Rest, reflection, alone time, low intensity exercise like walking, reviewing past work

This begins when you start your period. The first day of your period is the first day of your menstrual cycle.   

  1. The menstrual phase happens if an egg from the previous cycle isn’t fertilised (it didn’t meet any sperm). This means pregnancy hasn’t happened.
  2. This causes the hormones oestrogen and progesterone to fall.  
  3. The thickened lining of your uterus, which develops to support a pregnancy with nutrients, is no longer needed, so it gets shed through your vagina- this is a period.  

What is a period?
A period is a combination of blood, mucus and tissue that is released from the uterus through the vagina because pregnancy hasn’t happened. The average age to start a period is age 12 but some people will start years before this or years after. It’s common to have irregular periods when you first start them.  
Find out more about periods

Days 1-12: Follicular Phase


Follicle Stimulating Hormone (FSH), oestrogen and testosterone rising after period

Discharge and vaginal mucus

Starts off dry after your period and gradually becomes more wet. It may be white and cloudy in the lead up to ovulation  


Higher energy, improved mood, increasing sex drive, better concentration

Time for

Socialising, trying/creating new things, high energy workouts

The next stage is happening at the same time as your period. It starts with the first day of your period and ends when you ovulate (when the ovaries release an egg) and typically lasts between 10 and 22 days. 

The follicle-stimulating hormone (FSH) is the key hormone in this part of your cycle. It causes your ovaries to produce follicles (fluid filled sacs) which contain an egg. One of these follicles, or sometimes two, grows more than the rest and this is the one that will be released by the ovary. The growth of this follicle causes an increase in oestrogen.  

What is Oestrogen?
Oestrogen is the feel-good hormone that is highest just before ovulation. It causes the lining of the uterus (womb) to thicken in preparation for a possible fertilised egg.  

Days 13-15: Ovulation Phase


Oestrogen, testosterone and luteinizing hormone (LH) 

Discharge and vaginal mucus

In the couple of days before and during ovulation discharge will be stretchy and look like raw egg whites; slippery and very wet. 


High energy, improved mood, increased sex drive, more confidence

Time for

Socialising, trying new things, meeting new people and high intensity/energy workouts or strength training

Ovulation happens at around day 14. As oestrogen rises because of the egg maturing, the luteinizing hormone (LH) is also released. This hormone is responsible for triggering a mature egg to be released from the ovary, also known as ovulation.  

Once released, the egg then travels through the fallopian tube, it is here that the egg will most likely meet a sperm if pregnancy is to happen. 

Ovulation happens at around day 14 and is the time when you are most fertile. If you want to get pregnant you should be having sex in the build up towards ovulation as sperm can live up to five days in the vagina and uterus. 

Days 16-28: Luteal Phase


Oestrogen and testosterone declining, progesterone rising 

Discharge and vaginal mucus

Less discharge or no discharge, dry, tacky texture  


PMS symptoms, declining energy levels, mood swings

Time for

Slowing down, lower intensity exercise, taking more time for yourself

If the egg isn’t fertilised, it will make its way to the uterus where it will be shed along with your next period. Oestrogen and progesterone levels have fallen during this phase. It is here that you are most likely to experience PMS (premenstrual syndrome) symptoms. PMS is different for everyone, but some common symptoms include: 

  • Bloating 
  • Breast swelling and tenderness 
  • Mood changes 
  • Headaches 
  • Changes in sexual desire
  • Food cravings
  • Trouble sleeping
  • Acne
  • Tiredness

If you’re symptoms are extreme or affect your ability to go about your daily life, it’s important you speak to a medical professional. It shouldn’t be just something you put up with! 

What is progesterone?
Progesterone is a hormone produced by the ovaries which prepares the uterus for pregnancy. Rising progesterone in the luteal phase after ovulation can cause some people to feel more drowsy and less anxious. Progesterone stays high for a few days after ovulation and stays high if pregnancy has occurred. If pregnancy hasn’t occurred, levels of progesterone will fall.   

How does pregnancy happen?

Pregnancy happens if a sperm reaches the fallopian tube and burrows into an egg. The egg then changes to stop any more sperm from entering. This is called conception and it can happen up to five days after you have sex.  

As an egg only survives for about 48 hours after ovulation, pregnancy is only possible if you are having unprotected sex in the days leading up to or during your ovulation phase. 

The fertilised egg will then move towards the uterus in the days after conception. When it gets there, it will attach itself to the lining of the uterus, this is called implantation. Some people may experience implantation bleeding about 7-14 days after conception. This can be mistaken for a period but it is generally a lot lighter than your period would be.  

The body will then release the human chorionic gonadotropin (hCG) hormone. This is the hormone that pregnancy tests detect – that’s why you should wait at least three weeks after unprotected sex to take a pregnancy test. HCG keeps the uterus lining thick to support the growing embryo.  

As progesterone, hCG and oestrogen levels are high, the uterus lining will remain in place, and you will most likely miss your next period. A missed period is often the first sign that most people have that they are pregnant.  


Your menstrual cycle continues throughout your life only stopping during pregnancy, if you get pregnant, or when you reach the menopause which normally happens between the ages of 45-55.  

Your periods stop when you reach the menopause because of lower hormone levels. Before this happens, lower levels of hormones can also bring other changes including hot flushes, brain fog, mood swings, anxiety and irregular periods. This time of hormonal changes before the menopause is known as the perimenopause.  


Can I get pregnant on my period? 

Because an egg only survives for about 48 hours after ovulation, pregnancy is only possible if you are having unprotected sex in the days leading up to or during your ovulation phase. Sperm can live inside the human body for several days, meaning you could get pregnant if you have unprotected sex up to a week before ovulation. 

If you have a shorter cycle, ovulation may occur very soon after your period meaning that it is possible you could get pregnant if you have sex when on your period. 

If you want to get pregnant, it’s helpful to track your menstrual cycle so you know when you are most fertile. You can also buy ovulation tests which track the level of luteinising hormone which peaks just before you ovulate. However, you should be having sex before this and not be leaving it until this day.  

If you don’t want to get pregnant, it’s important to use contraception each time you have sex, whether that’s using condoms, or another form of contraception

If you’ve had unprotected sex, which is sex without contraception or a condom, or your contraception failed (like if the condom broke or you missed a pill), you may be able to prevent an unplanned pregnancy by using emergency contraception within five days.  

How do I know when to see a doctor?

You are the best judge of your own menstrual cycle, if something changes, for example you notice unusual discharge, spotting or pain, it might be there’s nothing wrong but it’s a good idea to talk to a GP to check.  

Some people will experience period cramps just before and during their period. If these cramps affect your ability to go about daily tasks, affect other areas of your body including back, hips, or thighs, or require the use of painkillers, you should seek help. Again, there may be nothing wrong but there may also be things that can help make this part of your cycle more manageable.  

Other reasons you might want to see a doctor include: 

  • Periods that are shorter or longer than 2-7 days (five days being the average) 
  • Intermittent spotting during your period  
  • Heavy or light flow during your period 
How do I work out where I am in my cycle?

It’s really useful to know where you are in your cycle even if you aren’t looking to get pregnant or avoid pregnancy. Knowing what phase you’re in and how it affects you can help you: 

  • Be prepared for your period and be kinder to yourself on lower energy days 
  • Plan your social events or exercise around how you’ll be feeling  
  • Plan quieter and rest days around when you know you might have less energy 
  • Notice any changes to your cycle which you might need to see a GP about e.g. changes in discharge that aren’t normal, your period becoming irregular 
  • Spot any early pregnancy signs easier 

The easiest way to get to know your cycle is by tracking when your period is; this is the most visible part of your cycle and will help you understand how long your cycle is.  

You could do this with a normal diary and pen or by using an app to help you track it. Other ways include taking your basal body temperature every day (temperature before you get up or do anything in the morning), monitoring your discharge, recording your mood changes or feeling the texture of your cervix (harder and more closed nearer your period and softer and more open nearer ovulation).  

Some people choose to use track their menstrual cycle so they know when they are fertile and either avoid unprotected sex on those days or have unprotected sex on those days depending on if they’re looking to get pregnant or not. As a contraception method it is not the most effective and is only suitable for certain people’s lifestyles and people who would be okay with becoming pregnant in the next year. Learn more about fertility awareness

How do you know if you’re pregnant?

The easiest way to tell if you’re pregnant is if you miss a period. Most pregnant people won’t get a period but some people experience spotting or lighter/shorter bleeding. Changes to your bleeding pattern may be an indication of early pregnancy as implantation bleeding can be mistaken for a period. Implantation bleeding is lighter, more intermittent and slightly earlier than your period would be.  

Some people experience no symptoms in the first few weeks of pregnancy but others experience:   

  • Tiredness 
  • Nausea 
  • Tender and/or swollen breasts  
  • Needing a wee more frequently  
  • Light spotting 
  • Bloating 

If you’ve had sex that could end in pregnancy and experience any of the above, or even if you’ve had what you think is your period, it’s a good idea to take a pregnancy test to check.  

Pregnancy tests detect the levels of hCG hormone in your wee. This hormone indicates that you are pregnant. However, this hormone won’t be present immediately after unprotected sex.  

If you don’t want to get pregnant, you can use emergency contraception in the first few days after unprotected sex.

To take a pregnancy test, it’s best to wait 21 days (three weeks) after unprotected sex or after your missed period, whichever comes first.  

My cycle is irregular, should I be worried? 

It’s normal for your cycle to be irregular for the first year or two when you start or when you’re reaching the menopause. If you’re at neither of these stages there may be other reasons for your irregular cycle including: 

  • A change in routine (e.g. travelling, new job, stress) 
  • Any contraception you might be using including emergency contraception (link) 
  • Hormone imbalances 
  • Changes in weight or being under/overweight 
  • Early stages of pregnancy – if you’ve had unprotected sex it might be a good idea to take a pregnancy test (link) just in case  
  • Certain conditions such as polycystic ovary syndrome 

There are so many reasons, it would be hard for you to know without asking a GP. There might not be anything wrong but they will be able to give you peace of mind and potentially help you with getting a more regular cycle that you can be in better control of.  

More about irregular periods

How can I support my partner with the changes that the menstrual cycle brings? 

It’s really great you’ve made it to this page and you’re learning about how the menstrual cycle can affect people with uteruses. This is a great first step.  

Everyone’s menstrual cycle affects them differently, some don’t notice many changes while others do, so the best thing would be to have a conversation with your partner and ask them what their experience is like.  

If they want your support around certain times of the month it might be that you check in and ask where they are in their cycle or for you to keep an awareness of where they are.  

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