Thus, coitus interruptus is morally acceptable, but practically is not reliable as it requires considerable discipline for the man. The rhythm method is the only form of birth control acceptable to Roman Catholic teaching, but also common to Protestants. With some modern adaptations such as temperature monitoring and testing of vaginal mucous, the prevention of pregnancy by this method has been greatly enhanced. However, its reliability and difficulties in practical application limit its efficacy. There are only minor problems such as proper fitting and irritation associated with these methods, but again their ability to prevent pregnancy is limited by the efficacy of the methods themselves and their practical implementation before and during sexual passion.
Breast feeding has a feedback mechanism that can prevent ovulation.
As a single form of birth control, it may be the least reliable. However, it will decrease the incidence of pregnancies in sexually active women who nurse their babies. Generally, they contain both an estrogen and a progestin. Their primary method of action is to prevent ovulation. The pill even has positive effects to prevent ovarian cancer, benign breast disease, ectopic pregnancy, and other problems common to women.