If you do get a bleed, that's a very good sign you're not pregnant, just as if you weren't on birth control. But if you don't get a bleed even though you took your pills correctly, chances are it's just a fluke and you're still not pregnant. Different pills are more likely to cause missed bleeds than others, so if you find that this particular pill has you skipping bleeds more often than not, you might want to switch to another pill.