Early Period After Starting Birth Control: Causes & Solutions

Question
Dr. Rappaport,
I am 39 years old and started taking birth control pills about 9 months ago.  Last month and this month, my period started 4 days early.  I take the pills at the same time every night and have never missed one.  They worked exactly as they were supposed to the first 7 months, but these last two months my cycle has started early.  What could the possible cause be and/or what can I do to keep my cycle "on track"?
Thank you,
Joelle

Answer
The pills still are working as they should and you are still protected against pregnancy. It is not uncommon to have your period early or late. Usually, it will be exactly 28 days from the start of one period until the start of the next. Remember that this bleeding is not really a "period" but rather is a "withdrawal bleeding" from a drop in hormones during the  placebo pills (#22-28). This is not an exact science and the fact that you started your bleeding 4 days early for the past two months is normal. A cycle is considered completely within normal limits if your period occurs from 21-35 days from the frist day of your period until he first day of the next period. Don't worry about it.