Target has done so much research on people's buying habits, that if you use their card and shop there regularly, they can tell from your purchase habits, and changes in them, not only if you are pregnant, but the week of your due date. They track such information in order to send you coupons. I never accept store cards because I don't want their damned advertising. But this sort of personal tracking is another reason. They can figure out all sorts of stuff about you from your buying patterns, and they can sell that information to whoever they like. Some of that information will be used to send you advertising. Some might be used for more nefarious ends. The above (about pregnancy) gleaned from a recent Fresh Air podcast.