Level 1: Why do you get pregnant after taking birth control pills? Under normal circumstances, birth control pills are effective in preventing pregnancy. However, if it is used improperly or there are special circumstances, it may cause contraceptive failure. , if the medicine is missed, the content of the medicine is insufficient, the medicine interacts with other medicines, etc., it may lead to contraceptive failure. In addition, if you use emergency contraceptive pills, their effectiveness is not 100%, and there is still a certain failure rate. Level 2: What are the symptoms of pregnancy after taking birth control pills? You may be pregnant if you have the following symptoms after taking birth control pills: Your period is delayed or completely absent.