The following are ways to detect ovulation with some certainty, in order of decreased probability:
- A typical temperature rise on the BBT chart.
- An endometrial biopsy that shows typical changes 7-10 days after ovulation.
- An elevated blood progesterone level about 7-10 days after ovulation.
- Seeing on ultrasound a follicle that measures 18mm+ and not seeing it anymore several days later and seeing fluid around the ovary.
- A positive OPK (ovulation predictor kit)
- Ferning on the fertility microscope
- Mittelschmerz (ovulation pain)
- Cervical mucus changes like egg-white cervical mucus (EWCM).
One important way to detect regular ovulation is to keep a menstrual calendar. When you see your doctor, the menstrual calendar helps to explain your cycles.
Other ways to detect ovulation include checking for fertility signs such as watching for your mittelschmerz, and evaluating changes in the cervical mucus and the cervical position. But even with the typical fertile egg-white cervical mucus (EWCM), there is insufficient certainty that ovulation has happened. The major question is always, "how can I predict ovulation ahead of time?"
Besides calculating your ovulation based on your cycle length, prediction of ovulation is often done with OPKs. As soon as they turn positive, ovulation usually happens within 12-36 hours. You cannot predict ovulation ahead of time with the BBT curve. Obviously, a positive pregnancy test is the very best indication that you ovulated.