Home-Check Instant Ovulation Test is designed to detect the surge in Luteinizing Hormone (LH). The body always makes small amounts of LH but prior to ovulation it makes far more. This test device will detect the LH surge which happens in the middle of your menstrual cycle, about 1 -1.5 days before ovulation. A pregnancy begins with conception. A child is conceived when the male sperm successfully fertilises the female egg. Successful fertilisation is most likely during a 24-hour period following the LH surge. Since this window is only open once a month and for a short period of time, being able to predict the L.H surge is very helpful when trying to become pregnant. Home-Check Instant Ovulation test is highly accurate and sensitive. It can detect surge in LH levels as low as 20mlU/ml.