How Effective is Fertility Awareness? Examining the Research on Natural Birth Control
Study finds surprising data on the efficacy of a contraceptive app. How does it stack up against sympto-thermal approaches?
By: Amy Sedgwick
Not surprisingly, I field a lot of questions from potential clients about the research and efficacy of Fertility Awareness-Based Methods of birth control (FAM). As the wife of a medical researcher, and a graduate of the Department of Rehabilitation Sciences at the University of Toronto (where the importance of evidence-based practice was repeatedly pounded into us) I always find it interesting to evaluate and share what the research says about the work I do.
Unfortunately, from a study design perspective, evaluating the efficacy of birth control methods is very difficult.
For those familiar with research methodology, you’ll know that the gold standard is randomized controlled trials. However, it is essentially impossible to study birth control this way. It would be grossly unethical to insist that anyone use a birth control method that is not a good fit for them or could cause unplanned pregnancies (which by the way, is why the early research on the birth control pill was outsourced to countries with lower standards for research ethics). Nonetheless, a few studies in the 1970s-80s attempted to compare FAM with other methods using randomized controlled trials. Unfortunately the study designs and statistics were so flawed that a 2005 review of the literature concluded that none of them provided a reliable enough study design to draw any conclusions about their efficacy. As a result, we typically have to rely on prospective, longitudinal trials that look at rates of unplanned pregnancies over time for people using a particular birth control method. This is what is called a Pearl Index.
A Pearl Index is the number of unintended pregnancies per 100 woman years. In other words,100 women for one year, or 10 women for 10 years, etc.
The reason a straightforward statistic doesn’t work with birth control is that there is a high rate of people changing contraceptive methods midway through a study, changing partners, and even changing intentions (choosing to become pregnant). To make matters more complicated, some menstruators will ovulate more than once a month (if they have short cycles) while others will only ovulate every few months (if they have long cycles). So instead of simply calculating the number of unplanned pregnancies in a year, it is more accurate to calculate the number of unplanned pregnancies per menstrual cycle reported.
Since most people are not familiar with the Pearl Index, it is often presented as a percentage on informational sites and lay literature. However, it is important to note that the percentage quoted does not reflect the percentage rate that a method will work or not work, but rather the percentage of people who will avoid pregnancy in a year of using that method. For example, if condoms are listed as 82% effective, that doesn't mean that if you use condoms 100 times they will fail 18% of the time. It means that for every 100 people who use condoms as their only method of birth control for a year, 18 will become pregnant. This is what is called a “typical use” rate.
Researchers then usually try to correct for misuse of the method to produce a “perfect rate.” In the case of condoms, those pregnancies that resulted from known errors (putting on the condom incorrectly or only part way through sexual activity) would be eliminated to create the “perfect rate” measure. In this case, yielding a 98% perfect use efficacy rate for condoms.
Contraceptive efficacy rates need to be read with that distinction in mind.
Clients are usually shocked when I quote statistics about how FAM is nearly as effective as the pill. Where do I get that number from? FAM is a term that refers to an approach to tracking fertility that draws on one or more of the following physiological indicators – cervical mucus, BBT shift, and cephalad shift. When mucus and BBT shift are combined it is referred to as using a sympto-thermal approach. The Justisse Method of Fertility Management (the FAM I teach) is one example. Until recently, there had only been one large-scale study conducted on sympto-thermal approaches.
This study was published in 2007 in the journal Human Reproduction, using menstrual tracking data from over 900 women who provided a total of 17,638 cycles worth of data. It found that there were 1.8 unintended pregnancies per 100 women. This was the “typical use” statistic. In this case, typical use included user error – including incorrect charting, or having vaginal sex on a known fertile day.
In this study perfect use was calculated to be 0.6 pregnancies per 100 women.
With only one real study to draw on though, it’s hard to have a lot of confidence. That's why I was pleased to see a study come out recently examining the effectiveness of mobile-based fertility awareness apps for use as birth control (not to be confused with period tracking apps which are very different). This research was specifically examining the efficacy of an app that uses single data fertility awareness (in this case basal body temperature readings) to tell the app user whether or not they are fertile. This means the user is responsible for putting in basal body temperature readings (BBT). Users also had the option of entering data from LH strips (otherwise known as ovulation predictor kits). This study showed that in typical use, there were 7 unplanned pregnancies per 100 in a year.
While this efficacy rate is surprisingly high, what's even more exciting (to us) is that it highlights the gap that proper sympto-thermal education can fill.
Studies of fertility awareness methods that use either mucus or temperature alone have shown much lower efficacy rates than the Human Reproduction study that I described above. Using apps designed for sympto-thermal methods would likely yield a much better result. Furthermore, there was no required education on the part of the app users. Receiving proper education in the use of Fertility Awareness Methods reduces the likelihood of user error by providing training on the correct way to obtain accurate temperature and mucus readings. Thus, we would expect those who use a sympto-thermal approach to fertility awareness (with or without an app) and receive thorough education about how to chart their signs of fertility, would achieve the highest efficacy rates.
While my clinical record is by no means scientific, this has roughly been my experience. Among those who have committed to working with me at the highest level of education and support that I offer, there have been no unplanned pregnancies in the past five years. Among those who have taken my Eco-Contraception program, which requires a little more self-motivation and includes less one-on-one support, my clinical statistics echo that of the typical use from the Human Reproduction study (1-2 pregnancies per 100 women per year). Since there is no follow-up for the Green Your Birth Control in 30 Days program, we can assume that this program has the lowest efficacy.
I hope this helps clarify some of the confusion around birth control efficacy in general, and FAM efficacy specifically. You'll find more resources here on on blog, including how the Justisse method works, reviews of sympto-thermal apps, and tips for using FAM to address menstrual irregularities. If you're interested in implementing FAM as a birth control method in your life, we encourage you to check out our popular Eco-Contraception program. Have a question about FAM or our programs that you don't see answered? Send us a note!
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Kim & Amy Sedgwick love to discuss sex, periods, and all the other things we’re not supposed to talk about. The co-founders of Red Tent Sisters, they’ve been featured in every major Canadian news outlet and have become a trusted resource for women seeking natural (effective!) birth control, a more joyful sex life, and an empowered journey to motherhood.
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