Medical Basis


The information the monitors use to distinguish between fertile and infertile days are founded on some biological facts relating to the female menstrual cycle.

  • Women ovulate once per cycle. If on the rare occurance of more than one, this will happen within 24 hours.
  • After ovulation, the ovum can be fertilized for a maximum of 18 hours.
    After intercourse, male sperm are active and able to fertilize an ovum in the female body for no more than 3 to 5 days.
  • So, during a female menstrual cycle, there are a total of 6 days that a pregnancy can occur, 5 days before ovulation and the day ovulation occurs.


This graphic clearly shows processes of the monthly menstrual cycle and how they are reflected in the temperature curve. Download INFORMATION BOOKLET below to also see this graphic illustration. It is also available from the Family Planning page.