I've had them work both ways. With the ICs I used to use, it would get progressively darker, but I never got a true positive (test line as dark as the control). Since using the clearblue opks, I don't really notice it getting darker until- WHOA that's a positive. I usually O the day after I get the positive result. Hth
Hi Sylvia,
I've been using an opk each of the last two months.
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