Yes, it is possible to ovulate without ever seeing a positive OPK (or peak reading on your fertility monitor). OPKs are designed to detect the surge of luteinizing hormone in your urine. This is the last hormone to peak before ovulation and the hormone that is responsible for triggering the rupture of the ovarian sac. LH needs to surge in order for ovulation to occur, but in some cases, the pattern of your surge and the time you test (if you do not manage to capture the surge when you test) will not let you see a positive result. If you have a sharp LH surge, for example, you may take one test before your surge is detectable by your kit and another test when your LH has already begun to trail and is no longer detectable by the kit. Whether or not you see a positive OPK result, it is recommended to keep on having intercourse until ovulation is confirmed by a clear and sustained thermal shift and ovulation is detected on your chart.