All about Ovulation

Lesson 12

Lesson Objectives:

• Know what ovulation is and understand the significance of ovulation for fertility charting

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Fertility charting, as you now know, is largely concerned with identifying ovulation and then using this information to make other predictions and calculations about your cycle. Once you know when (and if) you ovulated, you can decide to take a break from baby-making intercourse, you can tell if intercourse was well timed for conception and you can get the most reliable due date calculation. You can also tell when you can either reliably take a pregnancy test or expect your period.

So, what exactly is ovulation?
Ovulation is the release of a mature egg (ovum) from the ovarian follicle. Each menstrual cycle, several ovarian follicles begin to mature and develop under the influence of pituitary hormones. Usually only one follicle develops fully. While the other follicles recede, this dominant follicle produces an egg which will be released and which can be fertilized. The growing follicle secretes increasing amounts of the hormone estrogen. Following peak estrogen production, there is a surge of luteinizing hormone (LH). The LH surge triggers the release of the mature egg from its follicle. This is ovulation.

After Ovulation
Once ovulated, the egg is picked up by one of the fallopian tubes and begins to travel towards the uterus in the fallopian tube. This is where fertilization, if it is to happen, takes place. The follicle that released the egg becomes known as the corpus luteum after ovulation and begins to secrete the heat inducing hormone, progesterone.

The lifespan of the egg after ovulation is just 12-24 hours, maybe even less. Fertilization must take place within this time frame. After this time frame, the egg begins to degenerate and is no longer capable of being fertilized. This seems like a very short window of time for conception to take place. However, sperm deposited prior to ovulation can survive in the female reproductive tract for a few days, so the few days before ovulation takes place are also considered fertile days.

Ovulation and the Cycle Phases
Ovulation is the event that defines the phases of the menstrual cycle. The phase before ovulation, when the ovarian follicles are developing, is called the follicular phase. The phase after ovulation is called the luteal phase. The length of the follicular phase may vary but the luteal phase length is generally constant from cycle to cycle for the same woman, lasting 10-16 days. When cycles are irregular, it is usually because ovulation occurred earlier or later than usual. Knowing when ovulation occurred allows you to see if intercourse was well-timed for conception and lets you determine your luteal phase length. Knowing your luteal phase length tells you when to expect your period or a positive pregnancy test result.

When does Ovulation take place?
Ovulation takes place, on average, about two weeks before your period, though it can vary from 10-16 days before the onset of menstruation depending on the length of your luteal phase. During an "average" 28 day cycle, ovulation is usually expected to take place between cycle days 13-15. Based on this guideline, many women are taught to expect ovulation around day 14 of their menstrual cycle. Many women, however, do not have average cycles and even those who usually do may see irregularities from time to time.

A typical menstrual cycle may be anywhere from 21 to 35 days according to the American Society for Reproductive Medicine. Some women even notice cycles that are shorter or longer than this. Ovulation, then, may occur much earlier or later than typical guidelines suggest. For example, ovulation may occur on cycle day 23 during a cycle that is 35 days long for a woman with a 12 day luteal phase while ovulation may occur on cycle day 10 for a woman with a 24 day cycle and a 14 day luteal phase length. This variation among women and from cycle to cycle means that there is really no simple "one-size-fits-all" mathematical formula to calculate your ovulation date without observing your fertility signs. However, it is possible to learn how to identify your own ovulation date and fertile signs by examining your fertility signals.

Detecting Ovulation
Your ovulation date and your time of peak fertility can be detected by charting your fertility signs. This is because our bodies produce signals that can alert us that ovulation is approaching and tell us when ovulation has passed. Fertility signs that indicate that estrogen levels are high and ovulation is approaching (and fertility is high) include observing increasingly stretchy and "egg white" cervical fluid and observing a high, soft and open cervix. Commercial devices such as ovulation prediction kits (OPKs) and fertility monitors can also tell us that ovulation is approaching by measuring the presence of estrogen or luteinizing hormone (LH) in urine. Charting your basal body temperature (BBT) allows you to pinpoint the day of ovulation and tells you when ovulation has passed because progesterone raises the basal body temperature after ovulation.

Next Lesson: Interpreting your Chart.