Standard Days Method, Rhythm Method, Sympto-thermal Method...What’s the Difference?

wrote this on June 23, 2014

The sympto-thermal method of fertility awareness (STM) is often confused with methods like the standard days method and the rhythm method, but not all "natural" methods of pregnancy prevention are created equal. Each of these methods involves abstaining from intercourse – or, alternatively, using a barrier method – during a certain portion of the menstrual cycle in order to avoid pregnancy. However, the sympto-thermal method is far more accurate (we’re talking on par with the pill, here) and has many additional benefits aside from preventing pregnancy. In this blog post, I’ll be discussing the biggest differences between these methods, along with some common causes for confusion, in order to clear up some misconceptions and show you that STM is actually quite wonderful.

The rhythm method is one of the most widely-known (and widely ridiculed) methods of natural pregnancy prevention. You know: What do you call someone who uses the rhythm method?! A PARENT! Hyuck, hyuck. But what is the rhythm method, and why isn’t it highly effective? The rhythm method was actually one of the first formal systems to use periodic abstinence to prevent pregnancy. A woman using this method predicts when she is fertile based on the lengths of her past cycles: her shortest-ever cycle length minus 19 is the start of her fertile phase, and her longest-ever cycle length minus 10 is the end of her fertile phase. The problem with this method is that past cycles cannot predict future cycles. Let’s say that a woman using the rhythm method calculates that her fertile phase will occur between cycle days nine and 25 based on this information. First off, holy cow…16 straight days of abstinence is a lot for just one cycle. But what if, this cycle, she comes down with the flu and she ends up ovulating 10 days late as a result? Her fertile window might not actually end on cycle day 25 like she thought, and now she’s at risk of becoming pregnant.

Now, what about the standard days method? This method isn’t quite so widely known, but it is incredibly simple to practice. Simple isn’t always better. This method can only be used by women with cycle lengths varying from 26 to 32 days, and users of this method are considered fertile between cycle days eight and 19. An 11-day fertile window is much more reasonable than the 16-day window with the rhythm method. So what’s the problem? Well, there are a few. First, the standard days method does not account for women with a luteal (or post-ovulatory) phase of less than 13 days. So what if a woman often has cycles that are 32 days long (which is within the method’s limits) but has a luteal phase length of 12 days? This means she may not ovulate until cycle day 20, which is outside of the specified fertile phase. The method says she is no longer fertile after cycle day 19, but if she has unprotected sex on cycle day 20 thinking she’s not at risk, then she is likely to become pregnant! The second problem is that, like the rhythm method, the standard days method cannot account for cycle variability. What if a woman’s cycles are typically between 26 and 32 days long, but this month her cycle is 36 days? Again, she’s at risk. Past cycles cannot predict future cycles.


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The length of your cycle can be affected by any number of things, and it only takes one incorrect prediction of the fertile phase to become pregnant. The sympto-thermal method of fertility awareness, unlike these other two methods, does not attempt to predict the fertile phase. Instead, it requires daily observation of two simple fertility signs – basal body temperature and cervical fluid – to accurately detect the fertile phase. It can even be used by women with highly irregular cycles caused by polycystic ovarian syndrome (PCOS), which is a huge no-no for both the standard days method and rhythm method. STM is also a great tool for women who are trying to get pregnant. Not only can it greatly speed up the process of getting pregnant, but it can also help in the detection of reproductive disorders that may lead to difficulty conceiving. To learn how to practice the sympto-thermal method, or for more information about its benefits, effectiveness, and uses, check out the free info on our website.

As you can see, not all natural methods of pregnancy prevention are created equal, and it’s truly a shame that the rhythm method has given all other natural methods such a bad rap. Education about these methods – including their differences – is likely to make many women realize that STM is a perfect fit for their lifestyle. Even if a woman decides not to use it, at least she’ll be more educated about the ins and outs of her body. And how could that not be an awesome thing?

Jennifer Aldoretta is the cofounder and CEO of Groove. She is an entrepreneur, engineer, and biohacker who is obsessed with periods, nutrition, hormones, and the microbiome.