What you might not know about ovulation

We know that it is essential to understand your ovulation schedule in order to pinpoint the short window of success for insemination timing. But women often learn — late in the process — that temperature charting and ovulation detection kits don’t always tell you what is important for you to know.

This insight on ovulation detection, and its methods, was submitted by board-certified Reproductive Endocrinologist Dr. Michael Zinger, from Choice Mom sponsor East Coast Fertility.

Regular, monthly menstrual cycles are suggestive of normal ovulation. However, monthly episodes of bleeding can occur even in women who are not ovulating. Episodes of bleeding without ovulation are usually related to thickening of the uterine lining, such that it becomes unstable and bleeds for several days. This is different from bleeding that occurs after ovulation.

First, let’s explain what is happening to your body during a normal cycle. Progesterone is a hormone that is produced in the ovary after an egg is released during ovulation. It normally takes two weeks for an egg to mature and ovulate, then two weeks further until progesterone declines. This decline of progesterone is what triggers normal, ovulatory menses.

The most accurate approach for verification of ovulation is not simply to record that you have had a period, then, but by measurement of progesterone in the blood. This should be done one week after expected ovulation; in a normal 28-day cycle, this would be three weeks after the start of the period. The test looks for the presence of progesterone. Progesterone production peaks one week after ovulation and then disappears after one more week. Thus, the presence of progesterone in a significant concentration is an almost certain sign that ovulation has recently occurred.

Progesterone causes a slight increase in basal body temperature, providing clues to the presence of ovulation without the need for medical intervention. The measurement of basal body temperature should be performed each morning upon first waking. A result that would verify ovulation will demonstrate an increase in temperature that matches the rise and fall of progesterone as described above (starting soon after ovulation, lasting for close to two weeks, and ending at the beginning of the next menses).

There are some significant disadvantages of basal body temperature charting, however. 1) The progesterone-related increase in body temperature is so subtle that it can easily get lost within normal variations, significantly limiting the accuracy of this approach. 2) Furthermore, the tedious morning chore of checking daily temperatures throughout the cycle serves as an unwanted, stressful, daily reminder of the ongoing struggle to conceive. 3) Also, because the unrelated background variations can be quite erratic, it can take many months before one can verify whether or not a consistent ovulatory pattern exists. This loss of time can be frustrating and could delay useful treatment.

It is also important to understand that basal body temperature charting cannot be used to time the introduction of sperm during the current cycle since ovulation would have already occurred by the time the temperature rise occurs.

Luteinizing hormone (LH) serves as the body’s signal for triggering ovulation. Although initially released into the blood, it accumulates in the urine and can be typically detected by over-the-counter urine testing kits without the need for physician consult. Because the kit measures the trigger for ovulation (LH) rather than something that results from it (progesterone and the resulting increase in temperature), it provides an indication early enough to allow properly-timed introduction of sperm.

The positive signal is typically detected on the day prior to ovulation. However, the kits are not accurate for everyone. Hormonal imbalances, such as PCOS, can elevate the LH level to such a degree that, in some women, the kit will read positive every day. It is best to note a negative reading when first testing and see it then become positive on a subsequent day.

To improve the precision of this approach, a fertility center can provide ultrasound monitoring. Through ultrasound visualization, the fluid around the egg can be seen to increase, creating an expanding pocket of fluid, known as a follicle. The size of the follicle provides an estimate of how many days may remain before ovulation. Then, after ovulation, the follicle usually appears collapsed. This ultrasound approach is often combined with LH measurement to provide adequate warning when ovulation is approaching.

The most accurate way to know when ovulation is occurring is to provide a substitute trigger, through an injection. Physicians time the injection to be done once the follicle appears large enough on ultrasound. In this way we know that the egg, which is in the follicle, is ready for ovulation. By preempting the body’s own trigger, physicians can schedule a specific time for ovulation to happen. We know that ovulation occurs about 36 hours after the injection. In contrast, measuring LH by urine test kits can only tell us which day the trigger begins, not the exact time.


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