ovulation
Meaning of ovulation: The second half of the cycle runs to a fairly fixed length, so it is the first half that decides when release happens.
Definition of ovulation
Ovulation is the release of a mature egg from an ovary, the event around which the menstrual cycle turns. A surge of luteinizing hormone from the pituitary gland triggers it, and the egg is then swept into the nearby fallopian tube, where fertilization can take place. It falls roughly midway through a regular cycle, although the exact day varies.
What sets the release in motion?
At the start of each cycle a group of fluid filled sacs in the ovary begins to grow under the influence of follicle stimulating hormone. Usually one outgrows the rest and the others wind down. The surviving follicle pours out rising amounts of estrogen, and once that level stays high for long enough the pituitary gland flips from restraining luteinizing hormone to releasing a sharp burst of it. Roughly a day to a day and a half later the follicle wall thins and gives way, and the egg is carried out in a small volume of fluid. Finger like fringes at the end of the fallopian tube sweep it inward. The emptied follicle does not simply collapse. It reorganizes into the corpus luteum, a temporary gland producing progesterone, which prepares the lining of the womb and holds the next cycle back until it fades.
Why does the timing move around?
| Phase | Length and behavior |
|---|---|
| Before release | Variable. Stretches or shortens with illness, stress, weight change, heavy exercise, breastfeeding and the approach of menopause |
| After release | Fairly consistent, close to two weeks, set by how long the corpus luteum survives |
Counting forward from the first day of bleeding therefore predicts release poorly in anyone whose cycles are not steady, because it is the first stretch that moves. Cycles that come at long or unpredictable intervals often reflect release happening late or not at all, which is a common thread in difficulty conceiving.
How is ovulation detected?
Several signals exist and they differ in what they can say. Urine tests pick up the luteinizing hormone surge, so they give warning shortly before release. A small rise in waking body temperature follows progesterone and therefore confirms release only after it has happened. Cervical mucus turns clear, stretchy and slippery in the days beforehand. A blood progesterone level drawn in the second half of the cycle shows whether release occurred at all, and ultrasound can track a follicle directly. Timing matters for fertility because the egg survives only about a day, while sperm can persist in the reproductive tract for several days, so the window in which conception is possible opens before release rather than after it.
Used in a sentence
Tracking of ovulation was discussed as part of the evaluation for the couple's fertility concerns.
Good to know
Ovulation, the release of an egg, is a distinct event from menstruation, the shedding of the uterine lining, though both occur within the same overall menstrual cycle.
Word origin
Where “ovulation” comes from
From Latin ovulum, meaning a small egg, the diminutive of ovum, meaning egg.