I am 27 years old and my wife is 24. I have a question in mind which is related to my wife. She is on birth control pills for the last 3 months. She is using tri-sprintec contraceptive pill. One of her friends got pregnant recently even after using the contraceptive pill. Could this be possible? What are the chances of getting pregnant on birth control pill regimen? Can a pill be fully trusted for achieving contraception?