Understanding Breakthrough Bleeding on Birth Control Pills

Question
I have been on birth control pills for 4 years.  I take the pill every night at approximately the same time.  3 days before my period I had some scant brown blood it appears.  What has caused this?

Answer
That's what it is:  breakthrough bleeding.  Artificial hormones cause it.  "Approximately" the same time could also cause it, since it's not EXACTLY the same time.  There isn't really a lot more that can be said about it.  I don't think it's something to worry about but you can keep track of it and if it causes you any more anxiety, you can mention it the next time you see your doctor.