I thought I would start a new thread to make this imformation easier to find! I spent ages researching this so guess that other people will have too! I have been using the Unitest LH Ovulations tests for the past 3 cycles and although they get gradually darker until day 16 (of my regular 31 day cycle) they are yet to go as dark as or darker than the control strip. On day 17 the test strip then dissapears and I'm then left with just the control strip. I was wondering if this was something that I should be going to my doctors about or should I just accept the darkest day as my ovulation reading? I emailed the suppliers of the test and they have replyed. Hopefully this is useful for other people too. Hi Claire In around 5% of ladies the urinary LH never reaches 25miu needed to give a positive result. This is quite normal for these ladies and they are usually ovulating. It does however make using Urinary LH tests quite difficult. We usually recommend a trial of 3 cycles, which you have done, and then to try differnet brand to see if you can find one that gives clear positive results, possibly a digital one. Thank you for contacting Access Diagnostics I think that 5% is actually quite a lot and maybe they could have this on the information on the ovulation test intructions! Hopefully this is helpful to someone out there!! Claire Happy BDing!