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Pearl index and contraceptive safety

In order to evaluate the various contraceptives according to their safety or effectiveness, the “Pearl Index" is used as standard. But what can this index tell us, how is it calculated and are the calculations really so reliable? We answer the most important questions about the Pearl Index.

What is the Pearl Index?

“The Pearl Index tries to make a statement about the safety of a contraceptive. It interprets the data collected for a particular contraceptive in such a way that it can be shown how many out of 100 users became pregnant despite using the contraceptive.

Thus, a Pearl Index of 2 means that two out of 100 women became pregnant despite using a certain contraceptive. This is also referred to as a “failure rate" of 2%.

The Pearl Index is also calculated from the method safety and the application safety. The method safety indicates how many pregnancies occur even though the contraceptive has been used perfectly correctly. The more practical safety of use, on the other hand, shows how many women – taking into account application errors that occur in everyday life – become pregnant unintentionally. If method safety and application safety are close to each other, one can assume a general safety of the contraceptive."

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How is the Pearl Index measured/calculated?

The lower the Pearl Index, the higher the protection of a contraceptive. But how can the Pearl Index be calculated?

The calculation is based on 1200 months of use (100 women within one year) of a contraceptive. The index then finds out how many of these 100 women became pregnant within one year using the respective contraceptive.

For example, with a Pearl Index of 2, two out of 100 women became pregnant in one year. If the Pearl Index is 0.05, for example, one in 2000 women became pregnant within one year.

Pearl Index: Strengths and weaknesses

“The Pearl Index is a good and easy-to-calculate point of reference for those who prefer to be on the safe side when choosing their contraceptives and for whom a comparison can be made easier with the help of this reference figure.

However, it is very important to remember that the effectiveness of a contraceptive always depends on its correct use. Unfortunately, the Pearl Index (PI) also has a few weaknesses, which we will list for you below.

1. The PI does not take into account the increasing probability of becoming pregnant over time.
2. In addition, some women have sexual intercourse more often than others.
Diseases such as gastrointestinal illness can also reduce the effectiveness of hormonal contraceptives.
3. Also, there are the aforementioned problems in using different contraceptives (link to category page on contraception). While some are very easy to use, others are much more complex.

To counteract this problem, the “Life Table Analysis" was designed. This not only takes into account the frequency of sexual intercourse and individual use errors, but also gives an indication of the women who have not become pregnant. This makes it possible to indicate a percentage of protected women for individual months.

The Pearl Index should primarily serve as a guide. It does not provide any information about the risk of contracting sexual diseases. Depending on your life situation and individual factors, it is important to talk to your gynaecologist.

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Pearl Index for hormonal methods

With hormonal methods of contraception, such as the pill or the hormone patch, it is first of all important to note that they are not a barrier method. Hormonal methods do not guarantee protection against sexual diseases such as herpes genitalis, chlamydia or HIV.

The most commonly used contraceptive method for women is the pill. About 31% of women take it and swear by its effectiveness. The Pearl Index of the pill is between 0.1 and 0.9 in most cases, which also makes it one of the safest contraceptive methods – according to PI.

However, this safety also comes at a high price, because the list of side effects is seemingly endless. Weight gain, hormonally induced mood changes, a feeling of tightness in the breasts, headaches or nausea are just some of the many possible side effects.

Pearl index for natural methods

Natural Family Planning (NFP) aims to do without the addition of hormones or chemical agents. Unfortunately, natural contraception is still often assumed to be extremely costly and unsafe or even to require surgery. However, this assumption is wrong.

The safest method of natural contraception is the symptothermal method, which is also used by the trackle contraceptive computer. With so-called perfect use, i.e. no vaginal intercourse during the fertile time, it has a Pearl index of 0.4. With protected intercourse it is 0.6.

The symptothermal method can determine your fertile window by monitoring changes in basal body temperature and cervical mucus. trackle simplifies this method, eliminates its flaws and makes it more digital. trackle is worn overnight while you sleep and records your core body temperature throughout the night. When you wake up the next morning, trackle sends the temperature data from its station to your app. For the analysis, trackle only needs your cervical mucus data. That's it! This makes the symptothermal method fun and safe to use.

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Alternatives to the Pearl Index

One thing is clear: the Pearl Index can help us decide how to use contraception. However, it is also susceptible to interferences that affect the result. Forgetfulness, illness or interactions with other medicines can affect many contraceptive methods and thus reduce their effectiveness.

For this reason, the Pearl Index can be supplemented by two additional variables to make it more reliable. For example, when examining the number of unintended pregnancies in 100 women over a period of twelve months, the Pearl Index can be broken down into Safety of use (practical PI) and Safety of method (theoretical PI).

Safety of use provides information about typical and everyday use of a contraceptive. Factors such as forgetting to take the contraceptive, gastrointestinal disorders or errors in use are taken into account.

On the other hand, there is method safety. It assumes that the contraceptive method is used completely correctly and shows a value that indicates the safety of a contraceptive method rather theoretically.

If we now look at these two values in a common context, we can conclude: The closer the method and application safety are to each other, the more accurate the Pearl Index is. The lower the Pearl Index, the safer the contraceptive method.

The Pearl Index: A good orientation

The Pearl Index is a good tool for comparing contraceptive methods and their safety. The Pearl Index makes it possible to find one's way through the variety of contraceptive methods and to make an initial choice. Nevertheless, it is always advisable to keep in mind: No matter which method you use – only correct use can give you safety and reliability. Therefore, if you have any questions about contraception, talk to your gynaecologist and get detailed advice on finding the right method for you. If you have any questions about how to use trackle contraception, please contact us at [email protected] – we look forward to hearing from you.

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Hormone-free contraception with trackle

With the trackle contraceptive computer, you can use contraception easily, digitally, safely and, above all, hormone-free. You know exactly when you can get pregnant and when you can't.