CDC on "Fertility Awareness-Based" (FAB) methods of contraception

"No medical conditions become worse because of use of FAB [Fertility Awareness-Based] methods. In general, FAB methods can be used without concern for health effects to persons who choose them. However, a number of conditions make their use more complex. The existence of these conditions suggests that 1) use of these methods should be delayed until the condition is corrected or resolved or 2) persons using FAB methods will require special counseling, and a more highly trained provider is generally necessary to ensure correct use."

http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5904a9.htm