• Karoline Heldt, CFCP

Effectiveness for Avoiding Pregnancy

Updated: May 18

Let’s talk numbers! How well does Creighton Model System (CrMS) really work for avoiding pregnancy? Let me first reiterate that CrMS is not another form of “birth control”. It is a true method of family planning in that it can be used to achieve OR avoid pregnancy at any time. It can also be used to understand and (with the help of your NaPro trained physician) diagnose and treat gynecological health problems! But the reality is, many women (myself included when I first learned about CrMS) are coming to the system to space children or limit their family size and it’s important to know: How well does it actually work?


According to this study, the method effectiveness for avoiding pregnancy in couples of normal fertility is 99.5%. The use effectiveness for avoiding pregnancy in these same couples was 96.8%. Ok, hold up, that study is old! It’s 2021 after all. So here’s the amazing thing - CrMS is SO standardized and so consistent that their effectiveness rates have not gone down in 30+ years of system use. Incredible.


Another question: why the disparity between “method effectiveness” and “use effectiveness”? And what do those terms mean? Often when scientists are looking at outcomes for family planning methods they use these terms to identify two sets of data. Method effectiveness is used to describe “how well should this method work, taking in account anatomy, physiology, biology, the method instructions and process”. In other words, if you lived in a vacuum and used this system in an absolute perfect fashion, what kind of outcomes do you see? And then, since none of us live in a vacuum and are very human, we have another set of data: use effectiveness. This tells us “what is the actual effectiveness we see being achieved with this method when put into practice?”.


96.8% use effectiveness to avoid pregnancy! That is truly amazing. So why did my doctor tell me that this would have a 1 in 4 chance of failing me? They were most likely referring to the CDC data which looks at this study. The CDC data on birth control effectiveness lumps all “Fertility Awareness Based Methods” (FABMs) into one category and the data says that they have up to a 23% failure rate. Or, in the way we’ve been presenting numbers, a 77% chance of avoiding pregnancy effectively. There are a few reasons why this study isn’t applicable to your use of CrMS.

  1. The study was a systematic review of multiple methods of FABMs. CrMS was not included in the study.

  2. The CDC bases their data on abstinence or use of condoms on days identified by your method as being fertile. Hold up. Condoms? I thought we were studying FABMs. When it comes to CrMS, if you are using a condom on a day of fertility, you are relying on the effectiveness of that condom (low) NOT the effectiveness of CrMS.

There is so much more to CrMS than just numbers. The positive impact on your health, your marriage, your self-esteem. But numbers are important too! People can very often have serious reasons for needing to avoid pregnancy and it’s extremely important that the numbers can support their use of the system in being able to avoid pregnancy for a season or indefinitely. To learn more about what makes CrMS so effective or how it could work for you, contact one of our FertilityCare Practitioners.

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