The question is: how often does the Pill achieve its birth control effectiveness by preventing implantation? This depends upon how often "breakthrough ovulation" occurs, and then upon how often fertilization follows.

Unfortunately, there is no precise way of determining when the Pill is working by preventing ovulation and when it is not. If it is going to be used as the primary form of birth control you must understand that there is always a possibility that the Pill may prevent pregnancy by causing an early, chemical abortion. If that is not acceptable to you then you should consider another method of contraception.

The Pill also has potential physical side-effects that should be considered when making this decision. Oral contraceptives may increase the tendency to develop strokes and heart disease, particularly in smokers on the Pill. Other side effects may include headaches, depression, and weight gain.3

Norplant and DepoProvera are relatively new birth control options on the American market, although they have been used extensively in other countries. They work in much the same way as the Pill, and should be avoided if you are concerned about their abortifacient properties. The physical side effects are similar to those of the Pill - many women also complain of excessive hair loss when using Norplant and DepoProvera.