Daysy works by measuring, recording and analyzing your basal body temperature. This is the temperature of your body at rest. Most scientific applications accept the body’s temperature immediately upon waking as a representation of the BBT.
There are 2 predominant hormones involved in the fertility cycle, estrogen and progesterone. Estrogen is dominant during the pre-ovulatory phase (follicular phase) of your cycle, the time from the start of your menstruation until just before ovulation. Immediately after ovulation, during the luteal phase, production of the hormone progesterone increases and remains at an elevated level until just before the next menstruation. Progesterone causes the basal body temperature to shift by approximately 0.2 degrees Celsius. Daysy uses a complex algorithm to determine the change in average temperature values between pre-ovulation and post-ovulation. When the change is recognized, your Daysy knows that ovulation has occurred and you are no longer fertile.
Initially, Daysy determines your fertile window based on statistical data. Statistically, women can ovulate as early as day 11, so Daysy begins the red days around day 6 or 7 depending on the length of your menstruation. The red days will continue until Daysy has been able to confirm ovulation. In the beginning, Daysy is very cautious and it could take up to 5 or 6 days for Daysy to be certain that the temperature shift was in fact due to ovulation and not some other factor. Over the course of the first few cycles, as Daysy learns your unique fertility rhythm, it will slowly and cautiously reduce the number of red days. Daysy will begin to pinpoint your ovulation and start your fertile window (red days) to 5 days before your earliest ovulation. The fertile phase will then continue until ovulation has been confirmed.