A woman can achieve pregnancy during a maximum of 6 days in each cycle. These are the days directly before ovulation and the day of ovulation itself. Being able to identify your fertile window is valuable information when you are trying to get pregnant. While it is sometimes true that a woman has a ‘textbook’ cycle where ovulation occurs on cycle day 14 with a cycle length of 28 days, around 70% of women ovulate outside of the widely expected 13-15 day range.
One of Daysy's features is that she gives you a prediction of your ovulation and associated fertile window based on your previous cycles. This feature is mainly used by women to help them plan their pregnancies and their lives.
However, the prediction of ovulation is completely independent of the accuracy of the possible fertile (red) and infertile (green) days. There are a couple important items to note about Daysy’s ovulation prediction:
- The ovulation marker (white star) in your current cycle is solely a prediction of ovulation (see figure A), based upon everything the device knows about you so far. It is NOT a confirmation that ovulation has definitely occurred that day. Since it is just only a prediction, it is always subject to change based upon the progression of your cycle. You will know when ovulation has occurred in your current cycle when you begin seeing green fertility indicators (see figure B). The switch from yellow/red fertility indicators over to green is based upon the pattern of your day to day basal body temperature, not based upon the prediction.
- After you are 5 days into your next cycle, Daysy evaluates your previous cycle in its entirety and moves the marker from the predicted status to the calculated status, if different (see figure C).
The ovulation and menstruation predictions are set at the beginning of the cycle, and they remain static. However, Daysy is tracking your cycles in real time and giving accurate fertility indicators accordingly each day, regardless of the original predictions.
Pre-Ovulation Phase (driven by previous cycles)
Daysy’s ovulation prediction for the current cycle does not necessarily impact the pre-ovulatory green days, particularly after you have gone through the learning phase. When you first begin using Daysy, due to the lack of personal data in the early cycles of use, the algorithm assumes that all days after cycle day 5 and through ovulation could be fertile. This is adjusted by Daysy over time with more available data, in which infertile days during the pre-ovulation phase are calculated by learning from previously entered data and daily basal body temperature (BBT). Your earliest recorded ovulation confirmed by the corresponding characteristic elevated basal temperature is mainly responsible for your pre-ovulatory green days.
Ovulation Day Detection
Daysy was not designed to solely identify and isolate the predicted day of ovulation for the user, but also to identify the full potentially fertile window. Retrospective detection of a temperature shift closer to the end of the cycle is used to identify that ovulation has occurred.
Post-Ovulatory Phase (Temperature-driven)
After the fertile (red/yellow) days, the infertile post-ovulatory phase begins. Immediately after ovulation, the hormone progesterone is secreted by the corpus luteum. Progesterone has a thermogenic effect which causes the BBT to rise by approx. 0.2-0.3°C after ovulation. Due to the predominant secretion of the corpus luteum, progesterone levels and the associated increase in BBT after ovulation is a very constant retrospective indicator that ovulation has occurred. The status covering the post-ovulatory phase is temperature-driven and also not based on the predicted ovulation set at the beginning of the cycle. After ovulation is identified by a characteristic rise of BBT for a defined period of time over the average BBT of the pre-ovulatory phase, Daysy starts to assign post-ovulatory, green infertile days to the days thereafter. On each new day, statistical analysis is used to re-evaluate whether you are still in the high-temperature infertile luteal phase.