Justawaiting - an opk will only turn positive when th LH (lutenising hormone) surge is happening. OR when HCG (pregnancy hormone) is present in your urine or in the presence of some rare medical conditions. An opk will only show positive for the period of time that your LH surge is occuring. So, if you have a positive opk and your period is due it is possible and probable that you are pregnant. However, as the other women have said a pregnancy test showing a positive result is really the only one to count on.