Pearl index and safety in contraception

The “Pearl Index” is used by default to rate the various contraceptives according to their safety and effectiveness. But what can this index tell us, how is it calculated and are these calculations really that 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. He interprets the data collected for a specific contraceptive in such a way that it can be shown how many of 100 users became pregnant despite using contraception. 

A Pearl Index of 2 means that 2 out of 100 women became pregnant despite using a specific contraceptive. One then speaks of a “failure rate” of 2%.

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 at all?

The calculation is based on 1200 months of use (100 women within a year) of a contraceptive. So the index finds out how many of those 100 women got pregnant within a year using each contraceptive.

For example, with a Pearl Index of 2, 2 out of 100 women have become pregnant in one year. For example, if the Pearl Index is 0.05, one in 2000 women has become pregnant within a year.

Practical vs. Theoretical Pearl Index

In general, the Pearl Index can be divided into two subgroups: method security (theoretical Pearl Index) and application security (practical Pearl Index).

While method safety assumes that the contraceptive method is used correctly, application safety provides information about typical and everyday use of a contraceptive. Factors such as forgetting to take the medication, gastrointestinal diseases or errors in use are taken into account.

Pearl index in hormonal methods

The most commonly used contraceptive method for women is the pill. Around 31% of women in Germany take these and swear by their effectiveness. In most cases, the Pearl Index of the pill is between 0.1 and 0.9. This 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 feels endless. Weight gain, thrombosis, hormonal mood changes, breast tension, migraines or nausea are just a few of the many possible side effects.

Pearl index in natural methods

How secure is the trackle?

The Natural Family Planning (NFP) would like to do without the addition of hormones or chemical agents. Unfortunately, natural contraception is still often assumed to be extremely complex and unsafe or even to require an operation. However, these assumptions are wrong.



Diedrich, K. et al.: Gynecology and obstetrics. 2nd Edition. Heidelberg. 2007

Frank-Herrmann, P. et al.: Natural family planning today. Modern cycle knowledge for advice and application, 6th edition. Heidelberg, 2020