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Contraceptive Effectiveness

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Updated April 04, 2010

Fifty-three percent of unplanned pregnancies occur in women who are using contraceptives. When choosing a method of birth control women often consider the published success/ failure rates for the method they are considering. However, these rates are based on "perfect use" by women--that means using the method exactly as prescribed during every act of sexual intercourse.

The failure rates for a given method of birth control may actually be much higher during "typical use" than you might expect:

Typical Contraceptive Failure Rates

  • Implants and injectables
    2-4%

  • Oral contraceptives
    9%

  • Diaphragm and cervical cap
    13%

  • Male condom
    15%

  • Periodic abstinence
    22%

  • Withdrawal
    26%

  • Spermicides
    28%

Who is Most at Risk for Contraceptive Failure?

  • Cohabiting women.

  • Unmarried women.

  • Women who live below 200% of the poverty level.

  • Black women.

  • Hispanic women.

  • Adolescents.

  • Women in their 20's.

The success or failure of various methods of birth control vary according to several factors. An example can be seen in a recent article in the Journal of the American Medical Association (JAMA) that said "...adolescent women who are not married but are cohabiting experience a failure rate of about 47% during the first year of contraceptive use, while the 12-month failure rate among married women aged 30 and over is only 8%."

The failure rate for Black women is about 20% and apparently does not vary with income, while Hispanic women experience a 12-month failure rate of 16% and white women about 11%--rates that do vary by income and which are significantly higher among poorer women and lower among financially secure women.

Why Does Contraception Fail?

The reasons for contraceptive failure are complex and vary according to method:

Oral contraceptives may fail if a woman forgets to take them every day at the same time or if 2 or more pills are missed during a cycle and an alternative method of birth control is not used.

Diaphragms and cervical caps can be moved out of place by the penis thrusting against the cervix.

Condoms can break and/ or semen can leak from them: Period abstinence, or natural family planning, can fail if a woman does not accurately predict her fertile period: IUDs can be dislodged.

Withdrawal can fail if pre-ejaculatory semen enters the cervix or if the man is unable to withdraw his penis before ejaculation.

Tips for Effective Contraception:

  • Practice your chosen birth control method consistently.

  • Carefully follow instructions for the use of your birth control method.

  • Use alternative method of contraception such as a condom, if you forget 2 or more birth control pills during your cycle.

  • Certain antibiotics and other drugs can reduce the effectiveness of oral contraceptives--ask your pharmacist if this is a concern for you whenever you fill a prescription.

  • Take oral contraceptives at the same time each day.

  • Using a condom and spermicide with a diaphragm or cervical cap during your fertile period can result in almost 100% contraceptive success.

  • If you use an IUD, check for the string extending from your cervix monthly, if you can't feel it use alternative contraception and call your physician.

  • Call your physician immediately for emergency contraceptives after unprotected sex.

  • If you have any questions about the use of your birth control method--contact your healthcare provider--clearly understanding the proper use of your contraceptive will increase your chance of successful pregnancy prevention.

Remember, even one act of unprotected sexual intercourse can result in an unplanned pregnancy.

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