Perfect Use, Typical Use, Imperfect Use – What Exactly Does It All Mean?

An accurate understanding of FAM’s failure rate is a critical foundation for anyone’s confidence and willingness to use FAM as birth control (or any other birth control method, for that matter!)

In evaluating the safety of any birth control method, you need to understand the difference between perfect usetypical use, and imperfect use.  This information may already be well understood by many reading this blog, but it’s important enough to be repeated – especially because the term ‘typical use’ is actually fairly misleading!

Let’s consider how these terms apply to the failure rate of condoms.  The perfect use failure rate generally accepted for condoms is 2% per year.  This means that over the course of one year, when condoms are used correctly and consistently with every act of intercourse, 2 out of 100 women will have an unintended pregnancy.  According to Planned Parenthood, the typical use failure rate for condoms, however, rises to 18% per year – 18 out of 100 women who use condoms as their only form of birth control will experience unintended pregnancy.

18 out of 100 might seem like a lot (and it is!), but there are two issues to keep in mind when you consider ‘typical use’ failure rates in relation to your chance of getting pregnant with a particular birth control method.  The first is that while the perfect use failure rate only includes those couples who used the method correctly every time, typical use failure rate is gathered by observing the actual, real-world incidence of unintended pregnancies in a large group of women over the course of a year, including the people who used condoms correctly every time and all the incidences of incorrect use, such as removing the condom before intercourse has concluded, or even leaving the condom in the drawer entirely!

The second thing to keep in mind about typical use failure rates is that they are an average across a large number of users.  Your failure rate for a particular birth control method is going to depend on how consistently you use it and whether you use it correctly.  Typical use does not mean typical experience.  This is why it’s crucial that you choose a birth control method that meshes with your lifestyle. Make it easy on yourself to follow the rules – even the most effective birth control methods won’t stop you from getting pregnant if they are used incorrectly.

So, we’ve talked about condoms – what about the sympto-thermal method (STM), also known as the Fertility Awareness Method (FAM)?  I mentioned three birth control failure rates – perfect usetypical use, and imperfect use.  A dedicated study published in Human Reproduction in 2007 sought to find each of these failure rates for the STM by analyzing the incidence of unintended pregnancy in 900 women using the STM over the course of 24 months.

This study is a huge step forward in fertility awareness research: it is the first study on STM efficacy which documents sexual behavior throughout the cycle – including instances where the couples broke the FAM rules and engaged in risky behavior during fertile times.  Using this information, the researchers were able to differentiate between perfect STM use and imperfect STM use and compare the pregnancy rates between the two conditions.

According to the study, the perfect use failure rate for the STM is .6%, meaning approximately 1 out of 200 women who practice the method consistently will experience unintended pregnancy.  This number only takes into account cycles in which there was no unprotected intercourse during the fertile time (the failure rates for couples who abstained and couples who used barriers during the fertile time were virtually the same, by the way).  If you consistently follow the FAM rules each cycle, you can expect a pregnancy risk of .6% per year.

Imperfect use (also known as “user failure”) is where things get just a tad more complicated.  The researchers found that when they analyzed only the cycles in which unprotected intercourse occurred during the fertile time, excluding the cycles where the rules were followed, the pregnancy rate for those cycles was 7.5% per year.  Unfortunately, we cannot assume that if you break the FAM rules, you can expect a pregnancy risk of 7.5% per year – remember: this number is an average across many cycles where FAM rules were broken.  Your particular chance of pregnancy in any cycle where rules have been broken will depend on when you had intercourse in relation to your temperature shift and the qualities of your cervical fluid at the time.  The take-home message here is, if you break the FAM rules, your risk of pregnancy isn’t known – a 7.5% imperfect use rate averaged across many cycles doesn’t mean much to a couple who had sex on a very fertile day just before her temperature shift!

Lastly, typical use, reported by the researchers in this study as 1.8%, is the pregnancy rate of both the perfect use cycles and the imperfect use cycles combined.  If a large cohort of motivated, informed women uses the STM, including women who use it correctly every cycle and those who do not always use it correctly, we can expect 1.8 out of 100 women per year to become pregnant.

So what does this all mean for you, exactly?  My hope is that you’ll not feel frightened and out of control by high typical use failure rates for any birth control method.  As I mentioned before, typical use does not mean typical experience – you have more control over your fertility than those numbers might seem to suggest.  Your actions and conscious choices to adhere to your birth control method are the most influential factors in your chances of unintended pregnancy, whether you choose FAM as your birth control of choice, condoms, the pill, or whatever else you prefer.  So go forth and take charge of your fertility!

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