It really depends on the type of birth control method you are using and if you are using it correctly. I will assume that you are using the birth control pill.
If you have been taking a pill every day and have not missed any pills, then pregnancy is highly unlikely. As long as there was no gap of time between pill packs, the pill protects you from pregnancy even when the intercourse occurs on the first day of a new pill pack. However, if you did not open a new pill pack the day after you finished your last placebo or sugar pill (the last pill in your last pack) and there was a gap in time between your last pill pack and your new pill pack, then your risk of pregnancy is higher.
Women using the pill can expect their periods to be lighter and of shorter duration. A three day period is quite normal for pill users. Also, during the first few months of pill use, irregular menstrual bleeding (missed periods, bleeding in between periods, and spotting) is common. If you skip two periods in a row, take a pregnancy test just to be on the safe side. Do not stop taking your pills unless you test positive for pregnancy.
If you are using a different method of birth control, please submit a new question that specifies the type of method you are using.
9. May 2012
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