Context: Half of all pregnancies in the United States are unintended. Of these, half occur to women who were practicing contraception in the month they conceived, and others occur when couples stop use because they find their method difficult or inconvenient to use.
Methods: Data from the 1995 National Survey of Family Growth were used to compute life-table probabilities of contraceptive failure for reversible methods of contraception, discontinuation of use for a method-related reason and resumption of contraceptive use.
Results: Within one year of starting to use a reversible method of contraception, 9% of women experience a contraceptive failure--7% of those using the pill, 9% of those relying on the male condom and 19% of those practicing withdrawal. During a lifetime of use of reversible methods, the typical woman will experience 1.8 contraceptive failures. Overall, 31% of women discontinue use of a reversible contraceptive for a method-related reason within six months of starting use, and 44% do so within 12 months; however, 68% resume use of a method within one month and 76% do so within three months. Multivariate analyses show that the risk of contraceptive failure is elevated among low-income women and Hispanic women. Low-income women are also less likely than other women to resume contraceptive use after discontinuation.
Conclusions: The risks of pregnancy during typical use of reversible methods of contraception are considerably higher than risks of failure during clinical trials, reflecting imperfect use of these methods rather than lack of inherent efficacy. High rates of method-related discontinuation probably reflect dissatisfaction with available methods.
PIP: This study computed life table probabilities of contraceptive failure, discontinuation of use, and return to contraceptive use in the US. Data were obtained from the 1995 National Survey of Family Growth (NSFG) among a nationally representative sample of 6867 contraceptive use intervals contributed by women 15-45 years old who began use or resumed use after discontinuation during 1991-95. Analysis was based on Kaplan-Meier product-limit single decrement life table probability methods. Findings indicate that the risk of failure during typical use of reversible methods was 9% within 1 year of starting. Women with continuous lifetime use will experience 1.8 contraceptive failures. Failure rates were 7% for the pill, 9% for the male condom, 8% for the diaphragm, 20% for periodic abstinence, and 15% for spermicides. Failure rates reflect imperfect use. 31% of women discontinued use within 6 months of starting use. 44% discontinued within 12 months. Women using reversible methods continuously will discontinue use nearly 10 times during the reproductive period. Most women resumed use shortly after discontinuation. Low income women had higher risk of unintended pregnancy for all methods and the pill and lower risk of resumption after discontinuation. Hispanics had a higher risk of contraceptive failure for all methods and the condom. Black women had a higher risk of discontinuation of oral pills and condoms.