NFP is 75 percent to 87 percent effective at preventing pregnancy for women who have regular cycles and use it correctly. NFP may be less effective for women who:
NFP does not affect a woman’s menstrual cycle or hormones, and it does not require the use of chemicals or devices during sexual intercourse.
NFP does not protect against sexually transmitted diseases (STDs).
NFP requires close attention to many details, including daily temperature readings and testing vaginal discharge, which some women may find difficult to maintain. In addition, several months of record keeping are necessary before starting NFP in order for this method to be effective. For many women, it is a less effective form of birth control than methods such as the IUD.