How could I get pregnant on birth control?

Pregnancy on BC pill. Birth control pills aren't perfect, but they work very well if taken correctly. Missing a pill or pills may allow for an ovulation that cycle. Also taking an antibiotic may decrease the efficacy of the birth control pills for that cycle.
Method or use? All birth control methods fail: rates are calculated for baseline failures in the method, as well as failure when used incorrectly. Some contraceptive methods like iuds have only a 'method' failure rate, while birth control pills are subject both to method-failure and use-failure. Method-failure for pills is mostly failing to prevent ovulation, which is more common with low estrogen pills.

Related Questions

How quickly could I get pregnant after stop taking birth control pills?

Immediately. The pills are supposed to be taken daily and even preferably same time. You can get get pregnant after missing your pills for 2-3days. This humble doctor has a "personal experience", She is 13 next week. Cheers. Read more...