Your fertility app is wrong. Or is it?

How much should we trust our fertility apps when it comes to getting pregnant or avoiding pregnancy? Turns out, the little shortcuts offered by the pocket computers we call “phones” might not actually help us to do either. Or will they?

Your fertility app and your fertility

A recent paper published in the Journal of the American Board of Family Medicine reached the dramatic conclusion that most apps are bad for your family planning strategy.

“Conclusion: Relying solely on an app to use an FABM [Fertility Awareness Based Methods] , without appropriate training in the method, may not be sufficient to prevent pregnancy.” – Duane et al. (2016) The Journal of the American Board of Family Medicine

Each fertility app was evaluated based on its accuracy and authority*. Criteria were weighted based on importance to the user. “Very important” features such as accuracy and education are given 3x more value than “Helpful features” like whether or not moms can get it on their Android phone.  Some were prettier than others. Some were clearly designed by men (looking at you, Lady Cycle)

Accuracy was based on two criteria. One, effectiveness of the method under which the app’s prediction was based (although this seems unfair to those apps whose method is proprietary.) Two, comparing “evidence-based fertile days” to “app predicted fertile days”. The evidence-based fertile days were based on having women track their cycles using on Fertility Awareness Based Methods (see below for more info on these methods).

Importantly, the researchers failed to mention how many moms they tested (and whether they used 5 moms, 20 moms or 1000 moms is actually a really important thing!) They didn’t really go into what types of Fertility Awareness Based Methods they used to determine the “evidence-based fertile days”. They didn’t discuss whether or not they did real statistical analysis to evaluate any of the data in which they based their scoring. Overall, it seems that their score was assigned based on whether or not the app’s suggested fertile days fell outside of the evidence-based range on either end. Analysis ended there? Unclear from their paper.

While my science brain would have preferred a very clear end point – pregnancy or no pregnancy? – I know how difficult this type of study would be. In the least, I would have liked to see that they got as close as possible to physiological proof for ovulation by tracking hormone levels very closely. Since they are promoting their educational website about Fertility Awareness Based Methods, they might have a little bit of a bias towards how they set up the study to begin with.

With that said…

Which apps are good at detecting the fertile window?

This is going to be a very unsatisfying answer: we honestly don’t know that much… yet.

Keep in mind that this study looked at apps to AVOID pregnancy. Solid clinical research is slim to nonexistent when it comes to how the apps actually correspond to whether or not their users got pregnant during the prescribed fertile window. Even research on the pregnancy outcomes for standard Fertility Awareness Based Methods are slim. A review of the scientific literature in 2005 found only three trials studying Fertility Awareness Based Methods and all three of them had methodological issues. And the decade after that did not improve on this much as noted in a 2013 study which found only one solid clinical study for each method.

In the end, I chalk this one up to “take it with a grain of salt” until the evidence really rolls in.  If you don’t want to get pregnant, think about other ways you can avoid pregnancy. If you do want to get pregnant, consider really digging into the proven Fertility Awareness Based Methods and get over your squeamishness about checking your cervical mucus. Or pee on sticks. Lots and lots of sticks.


For those curious about Fertility Awareness Based Methods…

The most common Fertility Awareness Based Methods fall into four categories: Calendar-based, mucus based, sympto-thermal, and sympto-hormonal.

Ok, bear with me, I’m about to put my physiologist hat on.

Here is how your body cycles, in a nutshell:

You’ve just gotten your period, your body is gearing up for its next egg drop. A hormone called Follicle Stimulating Hormone (FSH) is released from the pituitary gland and travels down to the ovary to send the message about getting the next egg prepped. As this egg gets ready, the follicle (home of the egg in the ovary) starts releasing estrogen. Estrogen levels rise, rise, rise, until bam, a trigger in the brain signals the release of the next hormone from the pituitary gland – luteinizing hormone (LH). When LH spikes in the bloodstream, this is the signal to your ovary that it is ready to release the next egg. Egg pops out and the follicle transforms into a new structure called the corpus luteum which now shifts hormone production over to progesterone. Progesterone stays high if the egg is fertilized, takes the initial steps towards becoming an embryo and starts sending signals back to the corpus luteum to keep up the good work with progesterone production. No embryo, no signal, no more corpus luteum, no more progesterone, and the cycle starts again with your period.

Hormone cycles determining fertility LH spike for ovulation and timing conception

Science! The magical dance that your hormones do every single month. Picture from Hole’s Human Anatomy and Physiology 2010.

I tell you all of this because these these hormone signals create changes in your body that can be observed and quantified.  Once progesterone takes over the wheel, several changes occur that can be quantified  – cervical mucus changes from thin and watery to thick (time plug up the cervix!) and basal body temperature starts to rise a bit.  Perhaps you’ve learned enough from my little physiology lesson to realize that by the time progesterone gets into the driver’s seat it is too late. Hence the need to track a LOT of cycles before you start to see your own personal pattern emerge. Or you can pee on sticks. Lots and lots of sticks. Ovulation tests typically look for estrogen levels and LH, the exact hormones responsible for making an egg available for insemination.


Fun times with fertility tracking

If you’d rather avoid the investment in a bulk supply of ovulation tests, the Sympto-thermal Method is far and away the BEST method for planning out your pregnancy or avoidance of pregnancy. Symptothermal = Symptoms + temperature. Read: mucus checking + daily thermometer notes.  When done well, this method is just as effective as birth control for those avoiding pregnancy: there is <1% risk of pregnancy. Wow! BUT it requires a LOT of work. For one, you have to become a trained and diligent cervical mucus detective. Are you really up for the challenge? Not me.

The one that seems easiest, the Standard Days Method, is the only calendar based Fertility Awareness Based Method. This method only works for women with cycles that usually range from 26 to 32 days and classifies a fertile window as days 8-19 of the cycle. When done well, there is less than 5% rate of unintended pregnancy, but for most women, it is really a 12%  risk (I guess most of us suck at using calendars!)

Note, the Standard Days Method is still a rigorous Fertility Awareness Based Method, it is not the “Rhythm Method.” The Rhythm Method, apparently, is not really a thing in the world of science-based family planning. No really, it’s not a thing.


Back to those fertility apps…

Overall, I’m not terribly surprised that fertility apps are still finding their footing when it comes to fertility prediction. They are asking a lot of their users and need to make sure the education component is there so that users know what they are doing. It’s no surprise that the best scoring apps in the study are the ugly ones that rely heavily on education and diligent tracking.

If you’re like me and don’t want another baby and don’t want to do the work required to be a good little planner, you might want to consider other forms of birth control.

I still think the value in many of these apps is there – anything that helps a woman understand her body more ranks high in my book.  Although, some of the apps could use a little re-thinking (Yup, still looking at you, Lady Cycle)


The Pregnant Scientist is the alias under which Molly puts her PhD in Physiology to good use – digging into the scientific literature to share fun facts about pregnancy and parenting along with a few busted myths backed by solid research studies. Yay science!

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