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Ovulation Prediction Kits (OPKs)


How do Ovulation Prediction Kits (OPK) work?

Ovulation Prediction Kits are quite popular and can be quite useful to help you find your fertile time.

"Advanced OPKs" and Fertility Monitors using the same sticks are also available. These advanced sticks actually measure both Estrogen and LH and provide more advanced notice of ovulation. See below for more details.

Hormones, Ovulation and OPK

OPKs work by measuring the presence of Luteinizing Hormone (LH) in your urine. A surge of LH, which is sent to your ovary, causes your ovary to produce enzymes which in turn cause the dominant follicle to rupture and release the egg into the Fallopian tube. This is ovulation and it is expected to occur within 12 to 48 hours of the surge of LH.

A standard OPK is calibrated to detect the onset of the LH surge. Once positive it means that your surge has started and that the egg will be released shortly after.

Typically, the egg is released about 12 to 36 hours after the surge but this timing can vary greatly (denoted on the graph above by the red shaded area showing when ovulation can occur).

From a charting perspective, once the surge has started you may ovulate that day (depending on the timing of the OPK test and your own LH profile it may even have already occurred by the time you test) or up to 48 hours after due to the different timing of the observations.

To really know when/if ovulation actually occurred you will need to track your Basal Body Temperature (BBT). A progesterone test can tell you if ovulation actually occurred but not when it occurred.

Standard OPK

A standard OPK is a test stick which has a control line and test line. It is positive when the test line is as dark OR darker than the control line.

Some OPKs include a digital reader that look at the intensity of the lines and simply display a smiley when positive.

Advanced OPK

Advanced OPKs measure your estrogen level and LH levels.

LH detection provides the same information as the standard OPK. It gives you between 12 hours and 48 hours advanced notice of your ovulation. This corresponds to the Peak/Solid Smiley display.

Using the Estrogen detection capability, these sticks/monitors can also give you a few more days notice of your fertile window (High/Flashing Smiley display).

An advanced OPK displays a Low, High (flashing smiley) and Peak (solid smiley) fertility status based on your hormone levels. Enter this result in the corresponding data entry field (Monitor/Advanced OPK) on Fertility Friend (under Tests).

Note that Fertility Friend analyzes these data entries precisely so make sure to enter your data under the right field.

OPK Usage Tips

Following a few guidelines can help you get the most out of your OPK:

Reading and Recording Your OPK Test

For more details on reading and recording your OPK including a description of the available fields see the Reading and Recording Your OPK article.


Direito, Ana, et al. "Relationships between the luteinizing hormone surge and other characteristics of the menstrual cycle in normally ovulating women." Fertility and sterility 99.1 (2013): 279-285.

Strauss, Jerome F., and Robert L. Barbieri. Yen & Jaffe's reproductive endocrinology: physiology, pathophysiology, and clinical management . 8th Edition. Elsevier Health Sciences, 2018.

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