Factors that may impact the result of your basal body temperature measurement include:

  • Fever
  • Common cold
  • Inflammation / infection
  • Certain medications
  • Consumption of alcohol the previous evening
  • Cigarette smoking
  • Stress
  • Sleep disorders
  • Fatigue (physical and mental)
  • Change of morning rising time
  • Change of time zone
  • Long journey
  • Change of climate
  • Significant change in room temperature
  • Breastfeeding
  • Switching the thermometer type during the course of the cycle.

Even if you experience one of these factors, take your temperature, note it down, and describe the occurrence (you may do it in the tab Notes by the given day on the chart.) One or more unusual temperature readings don't necessarily affect the interpretation of your cycle, although they should be taken into account.