Contraception (birth control) prevents pregnancy by interfering with the normal process of ovulation, fertilization, or implantation. There are different kinds of birth control that act at different points in the process.

Every month, a woman's body begins the cycle that can potentially lead to pregnancy. An egg matures, the mucus that is secreted by the cervix (a cylindrical-shaped organ at the lower end of the uterus) changes to be more inviting to sperm, and the lining of the uterus thickens in preparation for receiving a fertilized egg.

Birth control is designed to interfere with the normal process and prevent pregnancy. Each method has its own side effects and risks, but some are more reliable than others. Although there are many different types of birth control, they can be divided into several groups based on how they work. Birth control choices include natural contraception, in which a couple has...