For the Calculating Fertile Days When it comes to a woman’s menstrual cycle, it’s important to know that the luteal phase (the second phase of the cycle, which begins after ovulation) always lasts 14 or 15 days, even though the total length of the cycle can vary from woman to woman. You can determine your ovulation day by subtracting 14 days from the average cycle length.
When does ovulation occur?
So if you have a 28-day cycle, ovulation occurs around the 14th day of your cycle. However, when calculating your fertile window, you should definitely take the days before and after into account as well. Although the egg survives for only up to 24 hours, sperm can survive for up to 5 days. It’s therefore possible that you could have unprotected sex a few days before ovulation and still become pregnant, because the sperm can, so to speak, “wait out” ovulation. You should always keep this in mind, whether you’re trying to conceive or want to avoid pregnancy at all costs.
Basal Body Temperature as an Indicator of Fertile Days
The fertile window can also be determined based on body temperature. The temperature rises by a few tenths of a degree (0.3–0.5 °C). However, this must be measured in the morning before getting out of bed; this is why it is also referred to as the basal body temperature (the standard nighttime temperature without physical exertion), because physical activity can always cause slight variations in temperature. You must therefore take your temperature daily in order to detect the slight fluctuations during your fertile window.
Cervical mucus also undergoes some changes during the fertile window —it becomes more transparent and fluid, and is produced in greater quantities.
Ovulation Tests
So-called ovulation tests are available at pharmacies. Like pregnancy tests, the test strips are briefly held under the urine stream and indicate whether you are currently in your ovulation phase (by detecting luteinizing hormone). If you are trying to conceive, the fertility indicator will tell you with about 90% accuracy whether you are currently in your fertile window.
