NFP Effectiveness - Fact or Fiction?

A note about studies. As of this writing, the effectiveness rates stated in this post can be found in the studies located on the Diocese of Lansing NFP website. Some methods have ongoing research, while others may not. I will not be updating this post to reflect future studies.

What is the effectiveness of NFP? I am asked this question all of the time. Unfortunately, many proponents of Natural Family Planning (NFP) will quickly reply, "99%" because that's what they've been told. The truth is that it's much, much more complicated than that, and most NFP methods are not 99% effective - at least not in the way most users think they are. Today, I will break down the types of effectiveness rates so you can feel confident when choosing a method of NFP. Note: this post also applies to Fertility Awareness Based Methods (FABMs ) since many people use FABM and NFP interchangeably.

Before getting too far in the weeds, let's talk about the word effectiveness. In most circles, when someone asks you if a method of family planning is "effective," they are asking you what the likelihood of them having an unintended pregnancy is. But NFP is not birth control. Many people use it to avoid pregnancy, but just as many use it to achieve pregnancy. And many are using it simply to track their cycles. Because of that, I never assume that the question "is it effective" automatically equates to "is it effective at preventing pregnancy?" For that reason, it is important to look at effectiveness rates for achieving pregnancy as well. However, that will not be addressed in this post (because it's already exceedingly lengthy). As of this writing, Creighton is the only method to study the effectiveness rates for achieving pregnancy. To further complicate things (as seems the norm with all things fertility), there are two types of effectiveness when avoiding pregnancy: Theoretical use (AKA perfect use) and Actual use. Theoretical vs. actual is where people's expectations for NFP and their lived experience conflict. In the world of birth control (the pill, patch, ring, implant, IUD, etc...), this is calculated using something called the "Pearl Index," which reports both the theoretical use and the actual use over a 12-month period of time. But because NFP is behavior-based and couples also use it to achieve pregnancy, it is very difficult to apply the Pearl Index to NFP methods (although some try). Another complication is that many NFP methods are not actually studied. They use other NFP methods' effectiveness rates and claim them as their own (more on this below). Despite these different factors, I am going to try and make this as easy to understand as possible.

Theoretical use is exactly what it sounds like. In theory, if everything goes EXACTLY to plan, how effective is this? If you are using the birth control pill, this would mean that you took it at the exact same time every day, never took a medication that enhances cervical mucus, like an antibiotic, and never skipped a dose. If you do all of these things, then the pill is 99% effective. But if you don't do all of those things, then it's about 92% effective. And before all you exceptionally technical people email me to complain that some pills are 90% effective and some are 93% effective, and the overall theoretical effectiveness rate is 98.6%, it's ok; I am lumping them all together. Because, really, no one would read a 40,000 word blog post, which is what it would take to list every type of birth control and all their effectiveness rates.

Similar to the theoretical effectiveness of birth control, NFP's theoretical effectiveness is determined based on perfect use. Did you follow all your method's instructions? Are you using the proper Basal Body Temperature (BBT) thermometer at the same time every day? Are you getting at least 4.5 hours of uninterrupted sleep? Are you peeing on the proper monitor strip? Is it expired? Do you have PCOS? Are you wiping from front to back and determining the sensation every time before AND after using the bathroom? Whatever your method is - are you following the instructions 100% of the time? That's right. One. Hundred. Percent. Of. The. Time. See what I did there with the bolding? If yes, then your method is likely 99% effective at avoiding. However, if you miss even one observation, or you have a medical condition that isn't compatible with your method, then you cannot expect that effectiveness rate. Instead, you can expect your specific method's actual use effectiveness rate. And this is where many people get frustrated and angry. Many people feel that they were given a bait-and-switch. I know this because in my diocesan work I have been yelled at (I'm not joking) about this more times than I can count. The actual use effectiveness rates vary wildly between methods and many couples find themselves thinking that they are getting a 99% effectiveness rate when they are actually getting closer to 90%.

There isn't enough time to go over each method's actual use effectiveness rates, but I can give you some examples. Creighton, for instance, has been studied extensively both by the developers and by others (including the founder of the Marquette method) and has been found to have an actual use effectiveness rate of between 96.8 and 98% at avoiding pregnancy. (I'd like to point out that the ACTUAL use effectiveness of Creighton is comparable to having yourself surgically sterilized or using an IUD). Likewise, the Marquette method (using the Clear Blue monitor only) has been studied and found to be 98% effective at avoiding pregnancy. NOTE: There are many different ways to use Marquette, and some of the other ways to use it are not as effective or are still being studied. Sympto-Thermal, on the other hand, has a lower actual use effectiveness rate. If (and this is a big if for many women) you have a consistent Basal Body Temperature (BBT) change, it is approximately 93% effective. If you choose not to use BBT it drops to 88%. But this isn't necessarily bad. Some couples avoiding pregnancy don't have as strong a conviction to avoid as others. For example, a school teacher who would like to time her conception so she can maximize her maternity leave might be more open to an earlier pregnancy even though it may present some logistical problems, whereas a woman undergoing chemotherapy who absolutely cannot get pregnant needs a more effective method. Because each couple's situation is different, there is no "best" method when it comes to avoiding pregnancy. The best method is the one that works for that couple. But I do feel strongly that couples are given the correct information about effectiveness rates so they can make informed decisions and choose the best method for them.

One thing that is often glossed over in the world of NFP is that many methods have not actually been studied at all, but claim to have high effectiveness rates (both theoretical and actual). These methods use studies on the Billings Method, Sympto-Thermal, and Marquette and then claim to be effective. However, NFP is taught by an instructor and learned and applied by users. Its effectiveness rate is based on the teaching and the couple's use, and each method uses different terminology, tracking, teacher training, and instructions for avoiding pregnancy. These things combined create the effectiveness rate of the method. Although it may seem like you can simply use the studies from one method and apply them to another method, you cannot. Just as the FDA requires all new birth control medications to be tested for effectiveness even if they are similar to other approved medications (because they're different), NFP methods should be treated the same. You cannot change terminology without changing the method. Period. Many newer methods track the same biomarkers, but they change the terminology, teacher training requirements, and instructions. They also might combine various aspects of different NFP methods and make some optional. For example, some methods allow you to optionally track BBT and LH on their app, but only train the teachers to teach and interpret cervical mucus. One study looking at combination methods and self-taught methods (I'm looking at you phone apps and social media groups) found an actual use effectiveness rate of around 87%. Interestingly, the effectiveness rate of doing absolutely no tracking whatsoever is about 85%. Now I'm not saying that these methods are bad, or that tracking with a phone app alone is bad, or that learning your method from your cousin's best friend's sister-in-law via social media is bad. I have just been yelled at enough to know that there are a lot of couples who use methods, thinking that they are very effective at avoiding pregnancy, only to find out (after an unintended pregnancy) that their method has never been studied. I've also counseled couples and explained that their method has never been studied, and they're fine with that. It just depends on what works for that couple.

Before I end this post, I do want to address two other common things that crop up in NFP circles. 1) How Creighton calculates unintended pregnancies and 2) Virtual vs. in-person teaching. First, some individuals have complained to me that the Creighton Model removes couples who would have been considered unintended pregnancies if the Pearl Index had been applied. In the original large effectiveness study of the Creighton Model (and other studies done by other researchers since), couples who chose to have intercourse on days that they knew to be fertile were not included in unintended pregnancies because they knowingly did not follow the instructions for avoiding pregnancy and instead knowingly chose to use the instructions to achieve pregnancy. These were not accidental pregnancies. These couples decided to have intercourse knowing they had a 76% chance of getting pregnant. In a later, famous study, the CEIBA study, researcher Dr. Joseph Stanford found that the Creighton model was 83% effective if you included people who knowingly had intercourse on a day of fertility, but who claimed to be avoiding pregnancy. But if you removed those people, then Creighton was 97% effective in actual use. This study was famous because Dr. Stanford assessed how effective the method was based on a couple's conviction to avoid pregnancy. He found that couples who strongly agreed that they were avoiding pregnancy had an almost 99% use effectiveness rate whereas couples who did not have a strong desire to avoid were much more likely to knowingly choose days of fertility to have intercourse despite stating at the beginning of the cycle that they were avoiding pregnancy. The developers of the Creighton Model have consistently stated that Creighton can be used to both achieve and avoid pregnancy. It is what the couple knowingly decides to do, in that moment, that makes the system either a system to avoid or a system to achieve. If a couple knows they can get pregnant on a specific day and chooses to have sex, they are using it to achieve a pregnancy. They are not using it to avoid a pregnancy. Creighton is not unique in this approach. The original Sympto-Thermal researchers removed couples who knowingly had intercourse on days of fertility as well. Additionally, even birth control that is assessed using the Pearl Index remove participants who stop using the birth control or use backup measures like a condom when assessing perfect use. Why? Because they aren't using the method being studied, so any resulting pregnancy or lack thereof isn't a true reflection of the method. Now, couples who miss a pill here or there are included in the actual use effectiveness data because that is reality, and it reflects how people take medication. But forgetting to take a pill on a Thursday that results in an unintended pregnancy is VERY different from using the Creighton model and actively having intercourse when you know you have a 76% chance of getting pregnant. And how do we know that they know? Because we teach it as part of learning the Creighton model, and we do pregnancy evaluations and ask if they knew the day was fertile - in two different ways. The heart of the conflict is that many people try to treat NFP like it's just another form of contraception. But it's not, and it needs to be studied differently.

Second, most NFP methods were developed and studied based on in-person teaching. While there were some teachers in various methods teaching NFP virtually before the Covid pandemic, the pandemic forced almost all teaching online. Because NFP is behavior-based and its effectiveness is influenced by both the teaching and the application of the instructions, the question is, "Does teaching virtually make NFP less effective?" The answer is "maybe." I know that Marquette had already studied their online teaching modality using the Clear Blue monitor, so those rates are likely accurate. However, the other methods have not done any studies that I am aware of. I have been teaching since 2016, and I can tell you that in some ways, teaching virtually is easier. Couples rarely miss virtual appointments; they are more flexible and able to stick to the follow-up schedule, and they tend to be more compliant with quick "chart checks." These things, in my experience, make it more likely for a couple to succeed. However, there was a big learning curve for me when I started teaching virtually. It was painful trying to get clients to send a clear copy of their charts in a timely manner, and getting essential paperwork back was a nightmare. These are things that eat into the appointment time and make it more likely that parts of the teaching schedule will get skipped due to time. These things can decrease the effectiveness of the method. However, the Creighton Model has since developed protocols to combat these challenges and ensure that couples and teachers alike succeed in sticking with the teaching schedule. So, time will tell if virtual teaching is as effective as in-person.

If you've made it this far reading, CONGRATULATIONS! If you skipped to the bottom for the takeaways, then here they are: First, actual use effectiveness is the rate you can expect to have an unintended pregnancy using your specific method (ask your teacher what those are). Second, not every method is studied for effectiveness. Third, if you are learning virtually and want the effectiveness rate stated by your method, then follow the instructions for learning, such as submitting charts ahead of time, etc. Fourth, the Creighton Model is between 96-98% effective (actual use) at avoiding pregnancy. Contact one of our Practitioners to get started. Happy charting!