How does the basal body temperature method work?

To use the basal body temperature method:

  • Make sure you have a thermometer that measures temperatures to at least one-tenth of a degree. This could be a regular digital thermometer or a special basal body temperature thermometer.
  • Take your basal temperature at the same time every day. The best time to take this temperature is immediately after waking up. Your body usually reaches its basal temperature when you are asleep..
  • Measure the temperature from the same place every day. The basal body temperature can be taken in the mouth, vagina, or rectum.
  • Record the temperature each day. Use a graph, list, or fertility-tracking app that allows you to compare each day’s temperature.
  • Identify a temperature increase. Basal body temperature typically rises less than ½ of a degree Fahrenheit after ovulation. It may take a few cycles to determine when this rise occurs each month.
  • Consider the fertile period. You are most likely to get pregnant during the period spanning 2 days before and 3 days after ovulation. If you are hoping to become pregnant, have sex during this time. If you want to avoid pregnancy, do not have unprotected sex until the fourth day after ovulation.

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