For a woman using Natural Cycles, the daily routine involves just 3 steps:

  1. After waking and before getting up, measuring her temperature in the mouth, under her tongue until the thermometer beeps, which takes less than 1 minute
  2. Entering her temperature data into the app (via mobile phone). Luteinising Hormone (LH) data can also be added, but this is optional
  3. Checking her fertility: Green = Not fertile (no need for protection during intercourse), Red = fertile (need for protection during intercourse)

After 3 months of usage, women with fairly regular cycles, who enter temperature data 5 times or more per week, can expect to get about 60% green days per cycle (i.e. no need for protection on these days)1.

The following factors may increase the number of red days identified:

  • Having recently stopped hormonal contraception
  • Highly irregular cycles
  • Atypical fluctuating temperatures2

1Berglund Scherwitzl E, Lindén Hirschberg A, Scherwitzl R. Identification and prediction of the fertile window using NaturalCycles. The European Journal of Contraception & Reproductive Health Care. 2015;20(5):403-408.
E.g. due to medical conditions (thyroid) or lifestyle (irregular sleep (+/- 2 hours than normal)), use of certain medication, a hangover from extensive alcohol consumption, insomnia, smoking or drugs, an infection or feeling ill, or working a night shift.

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