How Do OPKs Detect Ovulation

Ovulation Predictor Kits (OPKs) can help you in predicting your most fertile time of the month, known as ovulation. Easy to use and easy to buy, OPKs are wonderful tools for ovulation prediction and can greatly improve your chances of conception. Not only can an ovulation test confirm that ovulation has actually occurred, but it can also warn you of impending ovulation. Since the unfertilized egg has a short 24-hour existence and ovulation only occurs once per month, predicting ovulation correctly is extremely beneficial when trying to conceive.

Identifying Ovulation

Ovulation predictor kits work by identifying the reproductive hormone called luteinizing hormone, or LH. This hormone is ever present in your urine and increases 24 to 48 hours prior to ovulation. At the start of the menstrual cycle, your body commences production of the follicle stimulating hormone (FSH). This hormone aids in the formation of a follicle on one of the ovaries, which contains and nurtures the ovum. Once the follicle has developed sufficiently, a surge of luteinizing hormone forces the follicle to burst, releasing the ovum into the fallopian tube. This is the exact moment of ovulation.

The increased quantities of LH are sensed by ovulation predictor tests via anti-luteinizing hormone antibodies within the sensitive testing membrane of the kit. By detecting this sudden LH surge, ovulation tests help you predict, with great accuracy, exactly when you will ovulate.

A positive prediction on an OPK signifies that you will probably become fertile over the next three days. Peak fertility should then occur 24 to 36 hours after the positive ovulation test which indicated a surge in LH.

Timing Intercourse for Conception

Once you have received a positive result on an ovulation predictor test, it is then imperative to time your intercourse perfectly. The American Pregnancy Association recommends:

The three days immediately after a positive test represent the best time to have intercourse and increase the probability of getting pregnant. The first or second day will account for the day prior to ovulation and the third day should be the day of ovulation.

Fertilization will almost certainly happen 1 to 3 days after the LH surge. Therefore you will be at your most fertile approximately 24 to 36 hours after the LH surge.

Using Ovulation Predictor Kits

Be sure to follow the directions carefully when using an OPK. Some tests require you to hold the test strip in a container of urine for a few seconds. Other tests will instruct you to hold the test strip downward in your urine stream. Both are equally accurate and choosing between the two is just a matter of personal preference. Regardless of the test, the typical reaction time is five minutes. Each test has a control color line that signifies whether or not the ovulation test is working properly. This control line provides a baseline by which to interpret the test line results. If the test line color is darker or equal to the control line color then an LH surge has been detected. If the color is lighter then it signifies that no LH surge is present or that the LH that is present in the urine is at a normal level.

There are a few facts to consider when using an OPK. The most important of which is that there are some infertility medications that can confound the results. Clomid is one such medication that can cause a false positive ovulation test if you begin testing too early in your cycle. Drugs that contain FSH, LH, or HCG, antibiotics that contain tetracycline and hormonal methods of birth control can also invalidate test results.

It is possible to miss your LH surge, especially if you are one of the few women whose surge lasts less than ten hours. It is therefore suggested that if after a month of using OPKs you have not detected ovulation, you should consider testing twice a day. The recommendation is noon and 10pm, or at least eight to ten hours apart.

Works Cited:

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Last modified: April 14, 2014

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