Hi dear user, thanks for your query.
Decreased blood flow during menses is one of the advantage of oral contraceptive pills
. In your case, it seems to be the same. Brown discharge may be residual menstrual blood or it may be due to some local infection. If this is residual blood it will subside. But if it is due to infection then it will persist and you will need some treatment. Failure rate of pills ( used correctly) is very low i.e. 0.1. So, if you have taken them regularly then chances of pregnancy
Hope this helps.