If you are using ovulation tests to predict ovulation, pregnancy can affect the results of your tests. Because of the similarity in the hormones associated with ovulation and pregnancy, ovulation tests can turn positive both when you are ovulating and when you are pregnant.
Pregnancy tests measure the hormone human chorionic gonadotrophin, or hCG, to detect pregnancy. Once an egg has been fertilised, it travels down the Fallopian tube and implants in a woman's uterus. After implantation, the embryo begins producing hCG, which can be detected in the woman's urine. Home pregnancy tests detect this hormone at different sensitivity levels and turn positive when detected at those levels.
Ovulation is the release of an egg from an ovary each month. If this egg is fertilised, the woman becomes pregnant. Before ovulation, a woman's body releases luteinizing hormone, known as LH. This hormone is released in increasing amounts for several days before ovulation. Just before ovulation, LH surges, causing the release of an egg.
An ovulation prediction kit or test detects an LH surge in a woman's urine. These tests work in a similar way as pregnancy tests, but are read in a different way. Both a pregnancy test and an ovulation test have a control line and a test line. With a pregnancy test, two lines indicates a positive result. However, with an ovulation test, two lines do not necessarily indicate a positive result. Because LH builds up before ovulation, you will see two lines on a test for several days before ovulation. The result is positive when the test line is darker than the control line and the LH surge has been detected. When the LH surge is detected, ovulation will occur in 12 to 36 hours.
Ovulation Tests as Pregnancy Tests
Because of the similarity of hCG and LH at the molecular level, ovulation tests can detect pregnancy as well. The difference between hCG and LH is a beta subunit attached to the hCG. The website peeonastick.com illustrates the difference by describing LH and hCG as identical twins. The difference between them is that hCG is wearing a hat and LH is not. So the ovulation test will turn positive when it detects either one of the identical twins. But because pregnancy tests are also looking for the hat on the twin, a pregnancy test will not turn positive during ovulation. So if you are pregnant, an ovulation test will turn positive.
The sensitivity levels of ovulation tests are generally lower than the sensitivity levels of home pregnancy tests. Because ovulation tests are detecting the surge of LH, they are made to have lower sensitivities. If they are too sensitive, they will turn positive at the presence of LH. Because LH is present for several days before ovulation, ovulation tests must be made to predict high levels, or the surge, of LH. Ovulation tests have an average sensitivity of 30 mIU. And early home pregnancy tests can detect pregnancy at levels as low as 12.5 mIU, according to peeonastick.com. So a home pregnancy test will often turn positive before an ovulation test will turn positive.