Zakku:
Technically, your hormones are more level during pregnancy because they rise slowly (although to a fairly high level). That's different from normal cycles because they, well, cycle up and down. Birth control levels out the hormones by simulating *early* pregnancy. And only "monophasic" BCP will really keep the level constant. The others have different levels each week. The monophasic ones are the only ones that you can take without breaks between packs.