Birth control pills can affect pregnancy. Contraceptive pills are medications that avoid pregnancy and will prevent pregnancy after taking this pill. In clinical practice, there are emergency contraceptive pills and short-acting oral contraceptive pills. Emergency contraceptive pills are usually taken within 72 hours after unprotected sex. Short-acting oral contraceptives are those that are taken every day throughout the menstrual cycle. They can generally be taken on the first or fifth day of menstruation, with one tablet taken every night and stopped twenty-one days after taking the pill, and menstruation usually occurs 3-5 days after stopping the pill. Their mechanism of action is similar, on the one hand, they inhibit ovulation, on the other hand, they can inhibit the fertilized egg from being laid in the uterus, and they can also inhibit sperm from entering the uterine cavity. Therefore, after taking the pill, most women will not get pregnant.