Final answer:
The Billings Method is a natural family planning method that involves monitoring cervical mucus changes to prevent pregnancy, contrasting with barrier methods like condoms and diaphragms that block sperm, and irreversible options like sterilization with a vasectomy in males or tubal ligation in females.
Step-by-step explanation:
The Billings Method (also known as the Cervical Mucus Method) is a form of natural family planning. It's a behavioral contraception approach that involves monitoring changes in cervical mucus to predict fertile periods and thus prevent pregnancy by abstaining from unprotected intercourse during those times. The cervical mucus becomes more abundant and pliable at ovulation, indicating higher fertility, which is a key aspect that couples utilizing this method observe to determine when to avoid intercourse. This method does not involve any physical barriers or hormonal interventions.
Barrier methods, on the other hand, physically prevent sperm from entering the uterus, with common forms including condoms and diaphragms. Sterilization for males usually involves a vasectomy, and for females, it's typically a tubal ligation, both surgical procedures intended to be permanent forms of contraception. In the case of emergency contraception, options include the 'morning after' pill or insertion of an IUD, which can be used up to five days after unprotected intercourse to prevent pregnancy.