Knowing Your Menstrual Cycle
A woman’s menstrual cycle may be long, short, predictable or unpredictable. It may change from month to month and over the years, or it may stay pretty much the same. What is normal for one woman is not necessarily normal for another. But there are key changes in every woman’s cycle that can help you get to know what is normal for you. Whether you simply want to know more about your body, are trying to increase your chances of getting pregnant or want to avoid pregnancy, these information pages explain how the menstrual cycle works and what you can do to get to know yours better.
Periods are a normal part of a woman’s life from around the age of 10-14 until about 50. This regular (or not so regular) bleeding is the most noticeable sign of a woman’s menstrual cycle, but it is not the only sign. Getting to know the other, less obvious signs of your cycle can help you become more familiar with your own changing levels of fertility. The length of a woman’s menstrual cycle is calculated by the number of days between one period and the next.
A cycle begins on the first day of bleeding and continues up to, but not including, the first day of the next period. Women’s cycles range from 21 to 40 days or more, with an average of around 28 days. The length of a woman’s cycle may change a little or a lot from month to month.
Bleeding (menstruation) can last from 1 to 8 days, with the average being 4 to 5 days. The amount of blood a woman loses during her period tends to remain the same from one cycle to the next, but some women notice a change over time.
The menstrual cycle explained
When oestrogen and progesterone levels in a woman’s body are at their lowest – just before her period – two things begin to happen:
- The lining of the womb starts to shed. This is your period and is considered the beginning of a new cycle. If you are counting the days of your cycle, count the first day of bleeding as day one.
- At about the same time, the brain’s pituitary gland starts releasing a hormone called FSH (follicle stimulating hormone). The FSH triggers follicles (eggs in their sacs) to start maturing in your ovaries.
Menstruation to ovulation
Under the influence of FSH, 10 - 20 follicles start to develop, but only one of these (sometimes two) will mature fully. As the follicles grow, they release increasing amounts of oestrogen and this oestrogen causes the lining of the uterus to thicken in preparation for a fertilised egg. This stage of a woman’s cycle begins at the same time as menstruation and can vary greatly in length. It may last anywhere between 6 and 21 days and is called the follicular or pre-ovulatory phase. Women in this phase are considered semi or partly fertile because there is no way of knowing how many days it will be until ovulation.
Ovulation
Once the oestrogen produced by the growing follicles reaches a certain level, it triggers the pituitary gland to release a surge of LH (luteinising hormone). This causes the most mature follicle to burst open and release its egg into the Fallopian tube. This is ovulation.
Some women feel a slight twinge on one side of their lower back or abdominal area around the time of ovulation. Not every woman experiences this, but it is normal and is known as mittelschmerz (middle pain). Some women may also have discharge that is pinkish or a little bloody. If you have more than this little bit of bleeding between periods, tell your doctor.
The few days leading up to ovulation are considered the most fertile in a woman’s cycle. This is because sperm can survive for up to seven days in a woman’s body (on average they live for 3 days). If a woman has sex or insemination during the six or seven days before she ovulates, it is likely that the sperm will still be around by the time her egg is released.
One or two days after ovulation are also considered fertile days because a woman’s egg can live for about 20 hours after ovulation. If two eggs have matured, the second will be released within 24 hours of the first. From a few days after ovulation until her next bleed, a woman is generally not fertile.
Anovulatory cycles
Although ovulation occurs in most cycles, it is possible to have a cycle, and a period, without ovulating. This is called an anovulatory cycle and may happen in young women who have just started menstruating, women who are breastfeeding, women nearing the menopause, and women whose cycles are longer than 35 days.
Ovulation to menstruation
This phase is called the luteal or post-ovulatory phase. It is generally accepted that the time from ovulation to menstruation is always 12 to 16 days, whether your cycle is short, average or long. But while this phase does tend to be more constant than the phase before ovulation, recent research suggests it may range from 7 to 19 days.
After the egg has been released at ovulation, the empty follicle starts to produce progesterone as well as oestrogen. The progesterone causes the lining of the womb to secrete nourishing fluids. If the egg becomes fertilised, it plants itself into the womb lining and the follicle it came from continues to produce progesterone to ‘feed’ the fertilised egg.
If fertilisation does not occur, the follicle starts to break down and slowly stops producing hormones. When the follicle has broken down completely and is no longer releasing any hormones, the womb sheds its lining. This is your period. And so begins your next cycle.
Knowing your menstrual cycle — Physical changes to look for
Counting the days of your cycle can tell you how long your cycles are and whether or not they are regular, but the most reliable way to monitor changes in your fertility is by paying attention to clues from your body. Changes in your cervical mucus, basal body temperature and the position of your cervix can help you follow your cycle from start to finish. Some women chart all of these changes carefully to either increase or reduce their chances of becoming pregnant. Some women follow their cycles to know when to expect their periods, or to feel more in tune with their bodies.
Cervical Mucus
Mucus from your cervix changes throughout your cycle in response to hormonal changes. It’s a good marker of where you are in your cycle and checking your cervical mucus is quick, easy and reliable. Some women produce more mucus than others and may be able to see the mucus in their underwear. Others may need to feel the entrance of their vagina for it – use your fingertips or toilet paper. You can check your mucus at any time during the day.
At the beginning of your cycle, when oestrogen levels are low, you won’t have much mucus at all. This dryness means you are relatively infertile. This is usually just after your period, but if you have a short cycle, it may be at the same time as your period and therefore difficult to monitor.
A few days later, depending on the length of your cycle, your mucus will begin to increase. It may be sticky, white, milky or cloudy. This is a signal that you are entering your fertile window and nearing ovulation. If you are not using contraception and do not want to get pregnant, you should avoid sex from this point until a few days after you stop seeing egg-white mucus (see below). If you do want to get pregnant, this mucus marks the beginning of your fertile time.
Just before ovulation, a woman’s mucus becomes slippery, stretchy and clear – like raw egg-white. This egg-white mucus helps sperm move from the vagina through the cervix and into the uterus in search of an egg. This is the most fertile time in a woman’s cycle.
After ovulation, the mucus changes from the egg-white type back to a thicker, cloudier mucus. You may still be fertile if you see this mucus, but only for two or three days at most. Four days after your last egg-white mucus, you will be in the infertile phase of your cycle.
Your cervix still produces mucus after this point but under the influence of progesterone the mucus is thick, sticky and acidic. It stays around the cervix to block the sperm and many women feel a dryness compared to earlier in their cycles. Some women have no noticeable mucus during this stage, while others notice a thick or white mucus.
Checking your mucus is one of the easiest and most accurate ways to follow your cycle, but changes in mucus can be difficult to detect if you have a vaginal infection or use spermicide. Antihistamines can also cause your cervix to produce less mucus, making it difficult to check.
Changes in your cervix
You can also note the different stages of your cycle by feeling your cervix. To feel the changes in your cervix, insert one or two fingers deep into your vagina until you can touch what feels like the tip of your nose. This is your cervix. You may be able to feel an indent or dimple in your cervix. This is the opening to your uterus – called the os.
Changes in your cervix throughout your cycle
At the beginning of your cycle, your cervix should feel firm and low. The os will be closed. But as you approach ovulation, the position and feel of your cervix changes. It may feel softer and higher in your vagina and the os will feel more open. This means you are in your most fertile phase.
After ovulation, the cervix becomes firm and closed again and moves lower in the vagina. When the cervix has been like this for 3 days, you are no longer in the fertile phase.
It may take a few cycles to recognise the changes in your cervix and get to know what is normal for you. If you are trying to get pregnant or avoid getting pregnant, you may want to check your cervix at about the same time every day. This is the most reliable way to track changes.
Basal body (waking) temperature
Basal body temperature is your temperature first thing in the morning – before getting out of bed or doing anything else. You can’t feel these slight changes in your body temperature but a basal thermometer can detect them. You can take your temperature orally, vaginally or rectally as long as you use the same method every day. Before ovulation your temperature may vary from day to day by about 0.1 degree Celsius. Just after ovulation, however, your temperature rises by at least 0.2 degrees Celsius and remains high until your next period. This increase in temperature is caused by the progesterone released from the follicle after ovulation.
It is important to note that the rise in your basal body temperature doesn’t tell you when you are fertile or about to ovulate. It tells you when you already have ovulated. Women are most fertile the few days before their peak temperature, and are least fertile once their temperature has remained high for three days.
Tracking your temperature is the most demanding method of charting your cycle. You must take your temperature at the same time every morning, as soon as you wake up and after at least three hours of sleep. Going to the bathroom, having a cup of tea or moving around too much can all change your temperature and make it more difficult to see a regular pattern. Other things can also affect your temperature, such as illness or infection, alcohol and some prescription and recreational drugs.
If you are keeping track of your basal body temperature, it may help to keep daily notes of the time you take your temperature and any thing else that may affect the reading. Sleeping in for an hour longer than normal, for example, could result in a rise in temperature that looks like ovulation, but isn’t.
Other signs of your cycle
You may notice other changes that mark the different stages of your cycle. Some women regularly experience abdominal pain (slight or severe), swollen breasts, lower back pain and mood changes (both good and bad). These types of signs are not very reliable in pinpointing your fertile or infertile phases, but they may help support your other observations.
Knowing your menstrual cycle — Charting your cycle
A chart may help you keep track of the different changes that occur during your cycle. You don't have to keep track of all the changes, but you may get a better understanding of your cycle if you use more than one method. Choose what feels right for you.
Notes on completing the chart:
Temperature
If you are charting your temperature, remember to try to take your temperature at the same time every morning.
Also, try to note anything that may have affected your body temperature, such as alcohol or drugs.
It is possible to ovulate without seeing a noticeable rise in temperature. This can make it difficult to interpret your temperature chart, so if you are following your cycle to avoid pregnancy or to get pregnant, paying attention to other signs may help.
Other changes
Add any other changes you notice, such as bloating or swollen breasts, aggression, feeling tired or feeling sexual.
Menstrual cycle chart
print this blank chart for your own use
Knowing your menstrual cycle — Calculating your fertility
The calendar calculation method is a simple, though not very reliable, way to estimate when you are likely to be most fertile. To use this method, count the days of your cycle for at least 6 months. Subtract 20 from the length of your shortest cycle to estimate the first day of your fertile window. Then subtract 10 from your longest cycle to estimate the last day of your fertile window.
Example: If over 6 cycles, a woman’s shortest cycle was 26 days and her longest was 29 days, her calculation would look like this:
(shortest cycle) 26 – 20 = 6
(longest cycle) 29 – 10 = 19
This suggests her fertile window may be between days 6 and 19 of her next cycle.
Fertility monitoring kits
There are fertility monitoring kits on the market that may be useful in helping to identify the fertile and infertile days of your cycle. These devices tend to be expensive and some women find them difficult to read. But for women who want to gather as much information as possible (whether to get pregnant or avoid getting pregnant) or for women who find it uncomfortable to check their cervix or cervical mucus, these kits may be helpful.
Hormone monitoring devices measure hormone levels in urine to predict ovulation and determine which days you are likely to be fertile. The kit stores this information and builds up a record, or profile, of your personal cycles. The data is then used to help predict fertility.
Hormone monitoring devices are not recommended for women who have short cycles, long cycles, are breastfeeding or have Polycystic Ovarian Syndrome (PCOS). Read the package instructions before buying or using a monitoring kit.
Computerised thermometers and saliva tests are also available, but there is limited evidence about their accuracy.
Knowing your menstrual cycle — Special circumstances
After pregnancy or breastfeeding – After pregnancy, a woman’s body produces high levels of prolactin – a hormone that helps to produce breast milk. Prolactin also keeps oestrogen levels low which results in a woman’s menstrual cycle being put on hold. It generally takes about four weeks for a woman’s cycle to return after giving birth, but if she breastfeeds, it may be considerably longer.
Note: After pregnancy, about 50% of women ovulate before their periods return. This means they may be fertile again before they know it.
The cervix takes about 12 weeks to heal after childbirth and won’t feel the same as it did before pregnancy. Your cervix may feel harder and it probably won’t close as fully as it did before birth. Cervical changes will still occur, however, and can be used in monitoring your cycle after pregnancy.
Basal body temperature may also be disrupted following pregnancy, particularly if you are breastfeeding. At first there may be more changes in your temperature, and your readings may be lower than they were before pregnancy, but there will still be a distinct rise when you ovulate.
After stopping the Pill
The Pill works as a contraceptive by preventing ovulation. Once you stop taking the Pill, ovulation tends to return within a couple of weeks, but for some women it may take longer. Mucus and basal body temperatures may also be affected by leftover hormones from the Pill. This can make it difficult to follow your cycle for the first month or two after you stop using the Pill.
Other hormonal contraceptives
Hormonal injections, patches and implants can affect a woman’s cycle even after she stops using them. In some cases it may take many months for a woman’s cycle (and fertility) to return.
PCOS
Menstrual cycles of women with Polycystic Ovarian Syndrome (PCOS) are likely to be irregular, very long (more than 35 days) and often anovulatory.
Knowing your menstrual cycle — Resources and links
Books
Fertility by Dr Elizabeth Clubb & Jane Knight (David & Charles 1996) 3rd Edition. 192pp. This book is now out of print, but is available at the Women’s Health library. Much of the information is also available on the Fertility UK website:
NFPS - Homepage of The Fertility Awareness and Natural Family Planning ( NFP ) Service.
Links
www.ahealthyme.com - well written, easy to follow health website with pages on detecting ovulation, checking cervical mucus and charting basal body temperature. Click on women’s health and enter key words (eg. ovulation or fertility) in the search box. US-based.
Organisations
FertilityUK
Bury Knowle Health Centre
207 London Road
Headington
Oxford OX3 9JA
website:
NFPS - Homepage of The Fertility Awareness and Natural Family Planning ( NFP ) Service
An education and information service giving practical instruction in fertility awareness methods of family planning. Also trains health professionals on fertility issues.
WomanAware
8 Torrington Close
London N12 9TL
Tel: 020 8446 6648
email:
womanaware@purpleturtle.com
Runs courses on the menstrual cycle and fertility awareness. Contact WomanAware for dates of their next courses.
The menstrual cycle explained
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