I used OPK's after the first pg so I could determine when I should be ovulating rather than what I had been doing, which was assuming my "window of opportunity" was days 10 - 14 of my 28 day schedule. Turns out I was right anyway, I O around CD 13-14

. But it took 5 mo to get pg again. And I seem to be back on a regular cycle schedule again so now I just go by my CM and other bodily signs. I did use the Answer brand and liked them.