A woman is only fertile for a very short time period in her menstrual cycle. The days just before ovulation are best for sexual intercourse; these are called the “fertile days”.

Those trying for a baby should learn how to calculate when these fertile days are, so they miss as few as possible.


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How to effectively predict the day of your ovulation using two complimentary methods of measuring body basal temperature and the viscosity of cervical mucus

Sperm can wait for several days in the fallopian tube for an egg which is ready to be fertilised. Generally, it can be assumed that sperm survives for 3 to 4 days, but sometimes sperm can still be found in the body of a woman up to 10 days after sex.

However, it is not certain that sperm that has lasted this long is still capable of fertilisation.

As eggs only survive for between 12 and 24 hours, fertility begins to already decrease on the same day as ovulation. The fertile days therefore begin around 4 days before ovulation and end one day afterwards. In this time period, the mucus which is secreted by the cervix is thin and clear.

The consistence of this cervical mucus ensures that it is easier for sperm to find its way into the uterus. The vagina itself has a low pH-value to kill off any germs. This acidic environment does however limit the mobility of sperm. Cervical mucus, on the other hand, is alkaline and therefore establishes the best conditions for the sperm cells during the fertile period.

Calculate Your Fertile Days and the Ideal Moment

ovulation graphIf you are trying for a baby, the optimal time to have sex is the day before ovulation. However, the precise point of ovulation can be hard to predict exactly, so frequent sexual intercourse around the time of possible ovulation is recommended.

In order to predict the point of ovulation and therefore to calculate the fertile days, there are several possibilities.

The two following methods can of course be combined.


Method 1 – Ovulation Calendar

The better you know your body, the more easily you will be able to determine if your cycle is regular and if ovulation has occurred. If you observe your menstrual cycle over the course of several months, then you will be able to calculate your exact fertile days through your basal body temperature and the mucus from the vagina. Those who wish to measure this exactly can also use cycle computers or ovulation tests.

Measure Your Basal Body Temperature

work together as a teamThe hormone progesterone is responsible for raising the body temperature by up to 0.6 °C. As this female sex hormone is produced only after ovulation, measuring the body temperature in the mornings on a daily basis can give an indication of whether or not ovulation has taken place. It is important to measure the temperature as soon as you wake up, before you have even gotten up, as even sitting up in bed can cause a mild rise in temperature.

To obtain meaningful results using the temperature method, the temperature should also be taken at around the same time every morning. If you have slept for less than 5 hours, this can also affect the reliability of the results.

It is best to take the body temperature either rectally, vaginally or orally under the tongue, though the first two methods produce the most accurate results. Even when using a digital thermometer, which beeps after a shorter time period, you should leave the thermometer in place for at least 3 minutes, or up to 5 minutes if taking the temperature orally. It is also important to be consistent in the place you use to measure your temperature; once you have already measured it rectally, vaginally or orally, stick to this method for the whole cycle, as the temperature can vary in different parts of the body.

Overall, the body temperature method is a time-consuming way of calculating your fertile days.

Entering the Values

Begin the first day of your cycle (the first day of actual menstruation) with a new calendar sheet. Note your body temperature on the calendar sheet every day using a dot – later on, these dots can be joined up. Also make a note of the days when you had little sleep, or took the measurement at a different time, or had a cold or were otherwise ill.

As alcohol raises the body temperature, and various medicines, such as painkillers, lead to a decrease in temperature, days when these were taken should also be made a note of.

Evaluating your Temperature Curve

Pregnancy test - happy womanThe body temperature often falls by a few tenths of a degree shortly before ovulation. In contrast, there is a sudden rise after the egg has been released, which lasts until the end of the cycle. The temperature falls again shortly before or at the start of menstruation.

When the values on three consecutive days are a minimum of 0.2 °C higher than those of the preceding six days, then it is highly likely that ovulation occurred in the 48 hours before this rise in temperature. If fertilisation occurs and you become pregnant, the temperature remains at this higher level.

There are admittedly many factors which can influence body temperature, so the temperature curve doesn’t always look exactly like this model; it can therefore sometimes be more difficult to pinpoint the exact time period in which ovulation occurred. However, taking your temperature over a period lasting several cycles will improve the results of this method. While evaluating the temperatures, you can also consider the fact that the second half of the cycle always lasts between 12 and 16 days.

If you compare, for example, your temperature curves for your last five menstruation cycles, then you might be able to see that ovulation always occurs between the fourteenth and seventeenth day. From this, you can calculate your fertile days in the following cycle with greater accuracy. 

Possible Variations in the Temperature Curve

ovum fertilisation spermatozoaIf no increase in temperature lasting over several days can be seen, it is highly probable that no ovulation has occurred.

If the temperature only rises very slowly, or sinks again to a lower level before it should, this indicates a progesterone deficiency, which can be combatted by the use of monk’s pepper.

If there are a few anomalies in the temperature curve, then these are likely to be linked to stress, the consumption of alcohol, a change in the sleep cycle or the use of medication.

In cases where the cycle is very irregular, then the temperature curve only really indicates in retrospect that ovulation has occurred, and it is almost impossible to use this temperature curve to calculate when the next fertile days are going to occur.

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Method 2 – Cervical Mucus (Billings Method)

couple working together to conceiveThe secretion of the cervix, the cervical mucus, changes visibly over the course of the menstrual cycle because of the composition of the hormones in a woman’s body. It becomes particularly thin shortly before ovulation, so women who want to get pregnant can use this to help predict their fertile days by observing the consistency of their cervical mucus.

In order to use the Billings method reliably to calculate your fertile days, you will need to observe your cervical mucus over several months. It will take some time before you will be able to interpret it properly. A combination of this method and the body temperature method is therefore best.

The advantage of the Billings method is that the moment of ovulation is not merely pinpointed in retrospect, but predicted before it occurs. You can even document the consistency of your cervical mucus on the same calendar as your temperature curve, which would help you to check that your observations are in line with the rough calculations regarding ovulation from the temperature curve.

The Fibrosity of the Cervical Mucus

If you take the secretion out of the vagina between your fingers, then you should be able to feel a definite difference at various points in your cycle. Shortly after menstruation, there is very little, or sometimes no cervical mucus, so it can be rubbery and lumpy. It will become gradually thinner and runnier, and you should be able to stretch it a little bit between your fingers. A few days before ovulation, you should be able to stretch the mucus, which will look a little like egg-white, a few centimetres. Towards the end of the fertile phase, it will become drier and lumpy again.

Examining the Cervix

Menstrual Cycle Fertility ChartFeeling the cervix and the mouth of the uterus with your fingers can also provide information regarding fertile days, after a little practice. This is however only really beneficial for those women who do not produce much cervical mucus. The cervix is closed and low-down on the days which are not in the fertile period. It feels spherical, hard and smooth.

On fertile days, it is harder to feel the mouth of the cervix in a crouching position or while standing or sitting, as it is higher up. It feels softer and the opening, the mouth of the cervix, is easy to recognise as a foveola (a small dimple).

It will take a few cycles before you are able to use feeling the cervix to get any accurate information about your fertile days. You must examine it every day in order to take note of typical differences during your cycle.

  1. Be sure to stand or sit in the same position every day when you examine your cervix.
  2. Start shortly after menstruation has stopped.
  3. Empty your bladder before examining your cervix.
  4. Clean your hands well before examining yourself.
  5. Adopt a comfortable position (for example, sitting on the toilet, or squatting) and insert two fingers into your vagina.
  6. Move your fingers in a circular motion, feeling the cervix and mouth of the uterus.

Cycle Computers and Ovulation Tests

Cycle computers can help to evaluate the temperature quickly and accurately. They often come with an integrated thermometer and show on the screen immediately if you are fertile or not. They work even more efficiently if you enter in the texture of your cervical mucus. These relatively expensive devices do not, therefore, replace the measuring of body temperature and the observation of your own body, they simply make it easier to evaluate the results, as they create and evaluate the temperature curve themselves.

Some cycle computers work in a different way. Test strips measure the luteinising hormone (LH) present in urine in the morning. As it is an increase in LH which leads to the release of the egg, this is a further reliable way to predict ovulation before it occurs. For those women for whom the temperature method is unsuitable, either because they work shifts or have a very irregular cycle, these computers are a good, if not particularly cheap, alternative.

These test strips, which indicate a forthcoming ovulation, are also available individually (without the device). They are used like pregnancy tests and work in a similar manner. These ovulation tests can of course be combined with the approaches described above for a better and more natural family planning method. However, the results, even without simultaneously using the temperature method or the Billings method, are usually very accurate.

Plan and Relax

First of all, of you have not been trying to conceive for 12 months, do not panic. Enjoy this time alone with your partner – once a child comes into your life, your life will dramatically change – and practice lots of well-timed BMS (Baby-Making Sex). You can both immediately take natural fertility enhancing supplements, not do this with caution.

Certain herbs, roots and leaves have been claimed for centuries to alleviate so-called suboptimal fertility. However, none of these have ever been conclusively shown to increase fertility in empirical, scientific research studies.

Several common micronutrients, however, such as vitamins, amino acids and trace elements have been shown to dramatically improve sperm quality effectively, naturally and without side effects in double-blinded, randomised and peer-reviewed studies. We have reviewed the top 10 natural male fertility supplements available in the UK.

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