Perfect use of oral contraceptive pills have a 99.7% effectiveness at preventing pregnancy. However, oral contraceptive pills must be used accordingly. The first pill should be started within five days of the beginning of the menstrual cycle to be at maximum effectiveness. If the first pill is started at any other time, then seven consecutive days of pill use is needed.
If your periods have been regular up to now, then then there may be a chance of pregnancy. However, certain stressors such as excessive exercise or dieting can decrease the frequency of your periods. In addition certain drugs may decrease the effectiveness of oral contraceptives. The first test most doctors perform when a woman misses her period is a pregnancy test. Therefore, taking a pregnancy test either with store-bought urine tests or in a doctor’s office can help give you a definitive answer.