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Ovulation Prediction Kits  (OPK)

Luteinizing hormone (LH) is chemical produced  by the brain that causes release of the egg from the ovary (ovulation).  Ovulation usually takes place within 12 to 36 hours after a sharp rise  of luteinizing hormone in your blood known as the LH "surge". Ovulation prediction kits work by detecting the presence of the  LH surge in your urine.

If you are using an ovulation prediction kit, start testing about 3 days before the expected  day of ovulation. If you have  irregular cycles, use the length of your shortest cycle in the past six months to estimate when to start testing your urine. You can use the calcualtor below to estimate when to begin testing.

Days in cycle     

The best time to perform the test is around noon.

Follow the directions on the test kit. Usually about 5 minutes after the urine has been absorbed onto the stick the control band of the test strip will appear. The test is positive if the control band is present and the test band is equal to or darker in color to the control band.  If no visible control band appears at all the test is not valid. This usually means you did not apply enough urine to the test strip, and you will need to repeat the  test .


Continue testing every day until the test is positive.  Have sex  within 36 hours of testing positive.


Khattab AF, et al., The use of urine LH detection kits to time intrauterine insemination with donor sperm. Hum Reprod. 2005 Sep;20(9):2542-5. PMID: 15919775

See Also:
Fertility Charting
Ovulation calculator

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