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The Ultimate Guide to the Effectiveness of Evidence-Based FABMs

posted on November 17, 2018 by Lindsay Schlegel Lindsay Schlegel

When it comes to selecting a fertility based-awareness method (FABM) of natural family planning, there’s one question that’s of utmost importance: does it work?

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With the evidence-based FABMs being used today, the answer is a resounding yes, despite what popular opinion and perhaps even your doctor would have you think. There are two things to keep in mind when evaluating which method you can trust for your wellness and the future of your family.

The first is the difference between “perfect use” and “typical use.” Perfect use, or method failure, reflects how many unintended pregnancies occurred in a clinical trial, wherein couples followed every rule to a T, with no human error. Typical use reflects how the method is used in real life, when people make mistakes of varying degrees. Typical use is an average calculation. It includes those who didn’t follow the rules at all on some occasions and those who made minor errors on others. Your typical use will depend on how consistently and correctly you follow the rules of your chosen method.

The second thing to understand is that the Centers for Disease Control and Prevention (CDC) cites an overall FABM typical use failure rate of 24%, that is of 100 women who use them in a year, 24 will get pregnant. This data is flawed in a couple of ways. According to Dr. Marguerite Duane, a board certified family physician, Adjunct Associate Professor at Georgetown University, and co-founder of FACTS, the Fertility Appreciation Collaborative to Teach the Science, “The data comes from a retrospective survey based on patient recall, a flawed methodology, plus 86% of the respondents reported using variations of the calendar rhythm method, [which is not a modern FABM] which explains why the failure rate they report is so high.” The study also lumps together all FABMs with those who reported using no method at all. When you look at each method on its own, it’s clear that this isn’t an accurate representation of FABMs.

As you start to learn more about FABMs, you’ll quickly see that there’s a whole lot more to contemporary methods than calendar-based methods, which is the blanket term for the rhythm method (first formalized in the 1930s) and the standard days method (introduced in 2002). The rhythm method is calculated from a woman’s historically longest and shortest cycle lengths. This method has not been tested with contemporary clinical designs.

The standard days method is for women whose cycles range from 26 to 32 days in length, and it predicts she’ll be fertile for days 8-19 of her cycle. With the standard days method, the perfect use failure rate is 4.75% and typical use is reported as 11.96%.

While the standard days method, Cycle Beads, and apps developed from these models are natural forms of birth control, they don’t provide users with body knowledge about their signs of fertility and valuable health information. They also have lower effectiveness rates than methods that train women to chart their body’s unique fertile signs. 

What are the accurate numbers for FABM effectiveness rates?

Contemporary evidence-based methods of natural family planning track the various phases of a woman’s cycle each month via observable biomarkers, such as hormone levels (taken from a urine sample gathered first thing in the morning), basal body temperature (taken by mouth first thing in the morning), patterns of cervical mucus, or a combination thereof. You’ll find the studies that produced these effectiveness rates linked in their descriptions below.

The Sympto-Thermal Method (STM) combines basal body temperature (BBT) readings with observations of cervical mucus and sometimes that of the cervix itself. The perfect use rate for this method is 0.4%, and the typical use rate is 1.8%.

The Billings Ovulation Method uses cervical mucus observations to determine when a woman is fertile and when she is infertile. This universal method has been successfully taught to populations with low literacy rates, little access to technology, and even those who are visually impaired. With perfect use, the failure rate is 1%, and with typical use, it’s 10%.

The Creighton Model is a standardized modification of the Billings Ovulation, which categorizes observed mucus and uses color-coded stickers to interpret a woman’s chart. With perfect use, the method’s failure rate is 0.5%. With typical use, the failure rate is 4%.

The Marquette Model utilizes a ClearBlue Easy Fertility Monitor to track levels of luteinizing hormone and estrogen in urine. Variations on the method use cervical mucus or BBT in conjunction with hormone readings. With perfect use, the failure rate is 0.1%; with typical use, it’s 7%.

The Two Day Method is a method in which a woman asks herself if she noticed any cervical secretions today or yesterday. If either answer is “yes,” then she understands herself to be fertile. If both answers are no, she understands herself to be infertile. The perfect use failure rate is 4%, while the typical use rate is 14%. Though it sounds simple (and it is!), it is always best to learn any method from a trained instructor.

Comparing to hormonal birth control

When you compare modern FABM rates like those above to the rates for the Pill (perfect use 0.3%, typical use 9%), condoms (perfect use 2%, typical use 18%), and IUDs (perfect use 0.2%, typical use 1%), the relative risk of unintended pregnancy with FABMs simply isn’t there.

Every woman deserves to know the truth about the methods available to her today—especially those at low cost, with no side effects, and that can help achieve as well as avoid pregnancy. If you think the numbers cited here should be reflected in the CDC’s documentation on FABMs, click here to sign the petition for women to receive accurate information.

Update: The CDC has since updated its stated effectiveness rates of FABM, using more recent data. The CDC now states FABM failure rates range from 2 to 23%. Click here to read more about this update.

Click here to find an instructor in the FABM method of your choice.

If you’d like to read this article in Spanish, click here: “La guía definitiva acerca de la efectividad de los MBCF basados en evidencia.”



Posted by Lindsay Schlegel Lindsay Schlegel
Lindsay Schlegel writes frequently about fertility-awareness based methods, among other lifestyle topics. She writes for a variety of online publications, and her first book, "Don’t Forget to Say Thank You: And Other Parenting Lessons That Brought Me Closer to God" will be published in the fall by Ave Maria Press. You can find out more about her at LindsaySchlegel.com.

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