Ovulation

Ovulation is the release of a secondary oocyte from a mature dominant ovarian follicle. The timing is not reliably fixed by a calendar day. It usually occurs about 14 days before the start of the next menstrual period, so a regular 28-day cycle often places ovulation near day 14. In a shorter or longer cycle, the date shifts; the interval from ovulation to the next period is generally more predictable than the follicular phase that precedes ovulation. The fertile window is approximately six days: the five days before ovulation plus the day of ovulation. Fertile cervical mucus allows sperm to remain viable for several days, whereas the released oocyte remains capable of fertilization for only a short interval. For a person trying to conceive, intercourse during the days before ovulation is therefore useful, not merely intercourse on the presumed day itself. For a person avoiding pregnancy, a calendar estimate of “day 14” is not a dependable safe period. Ovulation marks the transition from the follicular phase to the luteal phase. After follicular rupture, the remaining follicular tissue becomes the corpus...