Final answer:
The term that describes the estimated rates of women who do not become pregnant using contraception is 'contraceptive efficacy' or 'contraceptive effectiveness'. This is often reported as 'failure rates', the percentage of women who do become pregnant during the first year of typical use. It varies based on how effectively the method is used, with perfect use resulting in a lower failure rate than typical use.
Step-by-step explanation:
The estimated rates of the number of women who do not become pregnant each year using each method of contraception are referred to as contraceptive effectiveness or contraceptive efficacy. These rates are expressed as failure rates, which indicate the percentage of women who become pregnant while using a given method of contraception during the first year of use. Typical use of contraception often results in a higher failure rate than perfect use, reflecting a more realistic effectiveness level in the general population.
For instance, barrier methods like condoms or diaphragms work by blocking sperm from entering the uterus and when used with spermicidal chemicals, the chances of preventing pregnancy are higher. On the other hand, reversible contraceptive methods like intrauterine devices (IUDs) are among the most effective while still allowing for the possibility of future pregnancy.
It is essential to distinguish these rates from the contraceptive success rate, which would be the inverse of the failure rate and represent the percentage of women who successfully avoid pregnancy using a specific method. In contrast, contraceptive failure rate is the number of pregnancies resulting from the method's use over a twelve-month period.