It detects the LH surge in your urine, which happens about 24 hours before you actually ovulate. When you get this LH surge on the urine stick, you should have sex that night and the next night (remember sperm live 48-72 hours- get them on board before ovulation on the day of the LH surge).
What does an ovulation prediction test tell me?
Wendy Fried, M.D., FACOG, FACS, is an OB/Gyn with Northern Obstetrics and Gynecology, PC in North Hills, New York
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