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Published Research

How Effective is Natural Cycles as Birth Control?

Illustration showing various birth control methods

Key takeaways

  • Natural Cycles has a typical use Pearl Index of 7 and perfect use Pearl Index of 2. Perfect use means that users don’t have unprotected sex on red days.
  • The effectiveness is similar globally and between groups.

This refers to how many users out of 100 per year become pregnant using a specific birth control method. When talking about effectiveness, we also refer to typical and perfect use. Perfect use reflects how a method is intended to be used, whereas typical use reflects how a method is actually used. 

For Natural Cycles, perfect use means that users abstain or have protected sex on all red days, while typical use includes all pregnancies that occur while using the app.

Fertility awareness-based birth control methods (FABMs), which are based on identifying the fertile window in each cycle, have previously been found to have a typical use Pearl Index ranging from 1.6 to above 20, and a perfect use Pearl Index ranging between 0.4 to 4.8. There are several fertility monitoring devices based on FABMs available on the market, but their contraceptive effectiveness is often unknown.

Natural Cycles shares similarities with traditional FABMs, but it’s also very different in a number of ways. With this in mind, we set out to investigate how effective Natural Cycles is as a birth control method in its own right. 

This study, which is one of the largest ever to be performed on a FABM, followed 22,785 participants from 37 different countries who used NC° Birth Control to prevent pregnancy. During the study period, they contributed a total of 18,548 years worth of data. We then analyzed how many of these users had become pregnant while using the app as birth control.

The results showed that with typical use, Natural Cycles has a Pearl Index of 6.9, meaning that on average just under 7 users out of 100 became pregnant during one year of use. With perfect use, the study found that Natural Cycles has a Pearl Index of 1.

Since this study, we have carried out further investigations into the effectiveness of Natural Cycles by looking at specific user groups, to see if the effectiveness stayed the same. So far, we have published two peer-reviewed papers that focused on users in the UK and in the US. The UK study included 12,247 users with 10,066 years' worth of data, and the US study included 5879 users with 5125 years' worth of data. The result of both studies showed similar effectiveness rates as the global study, with a slightly higher perfect use Pearl Index of 2. 

Since the perfect use Pearl Index varied between 1 and 2 in the studies, we report a perfect use Pearl Index of 2 in our marketing so that users are accurately informed when reading up on our effectiveness.

In summary, the results of these studies show that Natural Cycles’ effectiveness is comparable to other widely available contraceptives. They also show that the effectiveness rates of Natural Cycles are higher than what is generally seen in fertility-awareness-based methods.