In short, the effectiveness of Natural Cycles remains the same whether you use an oral basal thermometer, the Oura Ring or an Apple Watch. Natural Cycles is 93% effective with typical use and 98% effective with perfect use.
Natural Cycles’ effectiveness rates across all devices are closely monitored and Apple Watch effectiveness rates were validated in clinical trials that were evaluated by the FDA during our 510(k) process in which the FDA Cleared the Apple Watch integration. You can learn more about Natural Cycles' effectiveness here and about our clinical trials conducted here.
You may see a difference in temperatures from your thermometer and wrist temperatures from your watch – these are expected as measuring devices cannot and should not be compared. This is why two measuring devices (even if the same type of device) cannot be used at the same time - we provide more background on this here.