Understanding Ovulation and Identifying Your Fertile Window

Ovulation, also called the ovulatory phase, is the moment in your cycle when a mature follicle in one of your ovaries bursts open and releases an egg. That egg travels through the fallopian tube toward the uterus and is viable for fertilization for a maximum of 12 to 24 hours. Ovulation marks the boundary between the follicular phase and the luteal phase and is the central turning point of your entire cycle. No ovulation means no luteal phase, no progesterone rise, no period. Ovulation is not a detail. It is the heartbeat of your cycle.

A common misconception: many women believe that being fertile means having unprotected sex on the day of ovulation. In reality, your fertile window spans several days. Sperm can survive in the female body for up to five days. That means intercourse several days before ovulation can still result in pregnancy. Your fertile window therefore opens a few days before ovulation and closes with ovulation itself.

Many women try to predict ovulation using a calendar, for example the rule of thumb that ovulation happens on day 14 of a 28-day cycle. The problem is that ovulation does not happen on the same day for every woman or even in every cycle. Stress, travel, poor sleep, changes in weight or illness can all shift it by days or even weeks. Calendar methods can estimate ovulation but they cannot measure it. Daysy measures your basal body temperature every morning and detects the actual temperature rise that follows ovulation, precisely, reliably and based on your individual cycle.

Your body sends clear signals around the time of ovulation. Cervical mucus becomes clear, slippery and stretchy, similar to raw egg whites. Many women notice mild ovulation pain, a pulling or pressure sensation in the lower abdomen also known as mittelschmerz. Libido often increases noticeably. And basal body temperature rises by a characteristic 0.2 to 0.5°C after ovulation, a shift that Daysy measures and interprets every single morning.

Not every woman ovulates around day 14. Some women have very short cycles with early ovulation, as early as day 10 or even sooner. This can make family planning more challenging because the fertile window falls very early in the cycle. Daysy learns your individual rhythm and adjusts its analysis accordingly, whether your cycle is 24 days or 35 days long.

Regular ovulation is a sign of good cycle health. When ovulation doesn't occur, this is called an anovulatory cycle and can have various causes including severe stress, extreme exercise or eating patterns, hormonal imbalances or conditions like PCOS. Daysy detects through your temperature curve whether ovulation has taken place and provides valuable information you can bring to a conversation with your OB-GYN, midwife or healthcare provider.