Ovulation test strips, medically known as luteinizing hormone test strips, are used to qualitatively detect luteinizing hormone in human urine. It is an important indicator of impending ovulation, so it is often possible to detect peak levels of luteinizing hormone to determine the time of ovulation for the purpose of contraception or conception. Normal fertile women ovulate once a month and luteinizing hormone peaks 35 hours before ovulation. As sperm enters the female reproductive tract, it can survive for up to 3 days. If you have intercourse a few days before ovulation at this time, although the ovulation test results have not yet reached the peak, the sperm is very likely to survive until ovulation and result in pregnancy. There is also the case of environmental, emotional and other conditions, some women will suddenly advance or postpone ovulation. This situation, too, may make conception more likely. Therefore, it is not recommended for fertile couples to use ovulation tests to detect ovulation as a method of contraception.