How to accurately determine your fertile days

You want nothing more than a baby? How wonderful! Now the only question is when you are fertile and the chances of pregnancy are particularly high. But even if you don’t want to get pregnant at this very moment, it makes sense to track your cycle and know exactly which cycle phase you’re in.

The day on which the mature egg is released into the fallopian tube, i.e. the day of ovulation, cannot be per se linked to one day. Just as not every woman’s cycle is the same length every time, the time of ovulation also shifts. In addition, it can also happen that an egg does not mature in the ovaries in every cycle and therefore ovulation sometimes does not occur at all. Especially if you want to have a child, it is very important to observe each cycle individually so that you do not miss the fertile window and can really effectively increase your chances of pregnancy.

Once the egg is released into the fallopian tube, it can be fertilized for up to 24 hours. So once ovulation has taken place, fertilization can only occur within this window of time. This is why it is so important to be able to estimate the time of ovulation. Strictly speaking, a woman is only fertile at this time. Sperm can survive in the woman’s body for up to five days under ideal conditions. This extends the fertile phase, which is limited to just 24 hours, to up to six days. This means that, taking into account the viability of the sperm, the five days before ovulation and the timeframe of ovulation itself (due to the viability of the egg) are defined as the woman’s fertile days. Unprotected intercourse within this window of time is significantly more likely to result in conception than on other days in the cycle.

Despite popular opinions, it is not correct to assume that ovulation always occurs in the middle of the cycle (or indeed in every cycle). If you want to have a baby, it is extremely important to observe each cycle individually in order not to miss the fertile window and be able to effectively increase your chances of getting pregnant. The fertile phase actually only occurs once each cycle and maximum fertility is only given during a short window of time.

The breathe ilo method is based on the measurement of the CO2 content in the breath, which drops several days before ovulation. This makes breathe ilo an early indicator for the start of the fertile window, which is based on a real-time measurement. Methods based on the temperature method are categorized as a late indicator. The temperature rises when ovulation occurs and therefore ovulation can only be determined retrospectively. The detection of the highly fertile days before ovulation cannot be done in real-time and thus can only be derived by using data from past cycles. This only works for very regular cycles. Another common method is to measure the luteinizing hormone in the urine with ovulation test strips. The luteinizing hormone rises 24-48h before ovulation and thus makes it possible to detect ovulation 1-2 days before. The result can therefore not be compared to breathe ilo.

We get it: In the hope of being able to determine ovulation very precisely, ovulation tests are often used. However, there is a common misconception that a test can determine or predict the exact time of ovulation. You might imagine that after the morning test, the result would simply be a YES or NO for ovulation. Unfortunately, this is not the case. Ovulation tests measure the concentration of certain hormones in the urine. Shortly before ovulation, the concentration of these hormones increases. This means that you have to start testing early and regularly in order not to miss this fluctuation. The test device for the test strip has to determine a baseline in order to recognize an increase as such. 

In summary, this means that ovulation tests cannot determine the time of ovulation. Rather, they indicate the probability that ovulation will occur or has occurred. This means that it is not the WHEN but the IF that is indicated. There is no absolute value that can be used to indicate ovulation with 100% certainty. Since it is an increase to a basic value, which by the way can be different for every woman, it must be measured or tested constantly, depending on the method you have chosen. It is also important to mention here that the use of ovulation test strips produces a lot of waste – so this method is not particularly sustainable. In addition, the handling is not very hygienic, which is often criticized by women using this method.

The basal body temperature is measured each morning immediately after waking up. In the first half of the cycle, the waking temperature is the normal body temperature of about 36.5 degrees Celsius. After ovulation, it rises by at least two tenths of a degree Celsius. It remains this high until the next period. The measurement must be taken in the morning, immediately after waking up, and before getting out of bed. It is best to have slept for a few hours before taking the measurement. The measurement must be taken for at least three minutes and preferably in the vagina or anus. It is also important to always measure at the same place and at approximately the same time within one cycle.

It is also important to note that this method is susceptible to external influences. These include, for example, illness, lack of sleep, stress, time shifts, alcohol consumption, etc.

If the body temperature rises, this is a sign of ovulation. This means that if the basal body temperature is at least 0.2 degrees higher on three days in a row than on the six days before, the woman can assume that ovulation has taken place. If she is trying for a baby, this means that it is hardly possible to use or determine the fertile days in advance. It is only possible to use data from previous cycles to recognize a cycle pattern if necessary.

It happens time and again, especially with young women, that they have never heard the term ‘cervical mucus’ and they are often very confused about what the ‘discharge’ is all about. Well, we can reassure you: During the cycle, the mucus that is formed in the cervix and can be felt and seen at the vaginal entrance changes and is part of a healthy cycle. At the beginning of the cycle, the vaginal opening usually feels rather dry. The cervical mucus appears milky and cloudy and only becomes clearer in the days before ovulation. In addition, its texture changes from sticky and viscous to liquid and stringy (comparable to raw egg white). 

If you take some mucus between your index finger and thumb and pull it apart, you can see whether it is clear and spinnable or not. Clear, spinnable cervical mucus is a clear indication of the fertile window.

The symptothermal method is a combination of the temperature method and cervical mucus observation. A personal cycle chart can be created from the values that are recorded daily. Since this method links several body signs together, it is not possible to determine the fertile days exactly, but it is possible to narrow them down to about 12 to 14 days per cycle. 

Yes, you may not have known it, but the calendar method is also a method in its own right. It was developed by two doctors, Hermann Knaus and Kyusaku Ogino, and was originally intended to maximize the chances of conception. With the calendar method, you record the days of your cycle in a calendar for at least one year. Based on the records, you determine the shortest and longest cycle of the past twelve months. Then a specific formula is applied to determine the fertile days.

Another method is saliva testing, which can be done at home. It tests the hormones in the woman’s saliva to determine when she’s in her fertile window. It charts the natural fluctuations of the hormone progesterone, which typically rises around ovulation, reaches its peak in the days following ovulation, and falls again towards the end of the cycle, just before menstruation starts and a new cycle begins. This method typically uses single-use test strips, which unfortunately does not make this method very sustainable, as a lot of waste is produced over time.

Since the breathe ilo method is based on a real-time measurement, more precisely on the measurement of the CO2 partial pressure in the breath, which drops 4-5 days before ovulation, it is the ideal method to determine the fertile days of a woman. Especially if there’s a wish for a baby, it is important to be able to make full use of the fertile days before ovulation.

It has been known since 1951 that there is an alveolar CO2 drop a few days before ovulation. During this period, the alveoli induce a drop in the carbon dioxide content of the body. This effect is due to an excessive increase in respiratory frequency, a so-called hyperventilation. The cause is a change in the sensitivity of the respiratory centre to the CO2 concentration in the blood. In other words, you breathe faster during ovulation, which causes more CO2 to be exhaled and lowers the partial pressure of carbon dioxide (pCO2) in your body. This hyperventilation happens due to hormonal fluctuations and has so far gone unnoticed in women.

breathe ilo measures exactly this change in CO2 levels and allows a reliable prediction of the time of ovulation 4-5 days in advance, as the value of pCO2 is higher in the 1st phase of the cycle (follicular phase) than in the 2nd phase of the cycle (luteal phase). This makes breathe ilo the only fertility tracker that can determine ovulation early on. 

If you don’t feel like keeping a handwritten cycle diary, there are of course various apps you can use nowadays. Conveniently, you always have them with you on your smartphone. Some of these apps use graphics to illustrate the data entered and thus graphically show the fertile and infertile days. However, apps, which base their results solely on calculations, cannot provide a reliable forecast for your fertile days.

Nowadays, more and more women want to stop taking hormones. In recent years, the pill has become increasingly unpopular, partly because of its numerous side effects. Many women believe to have found a real alternative in the countless cycle tracking apps, some of which can be used free of charge. Usually, you have to enter some data in these apps: Cycle length, duration, and intensity of the period, mood swings, whether you have stress and/or drink alcohol regularly – the list is sometimes long and also quite personal. However, it is not advisable to use it for safe contraception, unless you already want to have a child and it wouldn’t be terrible if a pregnancy did occur as a result. This is because calculations are only mathematical and the apps therefore only provide average values. They cannot, therefore, provide reliable results.

The same principle applies here: ovulation and the onset of the period are determined purely mathematically by these apps. In most cases, existing data from previous cycles is used. The result? Again, an average value. Of course, there can be lucky cases, but usually they don’t determine the fertile window correctly. The length of the cycle can always fluctuate slightly, so average values cannot be relied on.

breathe ilo, on the other hand, offers a cycle app in combination with the breathe ilo fertility tracker. In this app, your fertile days are displayed accurately and reliably if the daily measurement with the breathe ilo device is carried out correctly.

Your cycle length is the period from the first day of menstruation to the day before the next bleeding starts. The first day of the cycle is always the day when the period starts. It is important to count from the day you notice fresh, bright red blood. Spotting, which usually appears light and brownish, does not count. The last day of the cycle is the day before the day of the next bleeding.  

As a rule, the menstrual cycle of healthy women can fluctuate between 24 and 36 days. Fluctuations are completely normal and no cause for concern. In hormonal disorders such as PCOS, endometriosis, due to stress or illness, during menopause, breastfeeding or after stopping the pill, it can happen that the cycles are much longer than 36 days. Irregular cycles would therefore be cycles that are shorter than 23 days and longer than 36 days. Nevertheless, ovulation usually also takes place during these cycles and can therefore be determined. In this case in particular, it is important to look at each cycle individually, to pay close attention to the body’s signals and not to rely solely on forecasts. Again: Slight fluctuations in the cycle are normal and can simply happen from time to time. Often these fluctuations are associated with stress and after the stressful phase the cycle quickly returns to a normal length. However, if significant fluctuations occur frequently or if the cycle is suddenly much longer or shorter, this can indicate a cycle disorder. Especially if you want to have children, this can quickly become a real problem. With a very irregular cycle, the fertile phase and thus ovulation is unfortunately also difficult to determine. In this case, each cycle should be considered individually and it is often advisable to discuss the issue with a trusted specialist in the medical field.

If you decide to use natural contraception, you should be aware that the basic prerequisite is to become familiar with the processes in your own body and to make a conscious effort to understand your body better. Yes, this can be time-consuming, but it’s worth it. By observing the symptoms that occur in both the fertile and infertile phases of the cycle, you learn a lot about your own body and, over time, get an intuitive feeling for your own cycle. Depending on your wishes, pregnancy can either be prevented or, along the way, your wish to have a baby can be fulfilled.