COMMENTARY

Choosing a Contraceptive Method: Consider Failure Rate

Peter Kovacs, MD, PhD

Disclosures

June 16, 2011

Contraceptive Failure in the United States

Trussell J.
Contraception. 2011;83:397-404

Background

To achieve a pregnancy, the proper function of 3 organs is required. These include regular ovarian activity, normal sperm production, and intact activity of the fallopian tubes and uterus. Multiple other factors influence a woman's chance for pregnancy, and among the most important of these factors is age.[1] From the age of 30 years, fertility rates decline slowly. By the time a woman is 40 years of age, her chances of becoming pregnant are reduced by half, and by the age of 45 years, they approach 0%. In most women, if contraception is not used, the chance for a successful pregnancy is approximately 25% in the first month and 85% by the end of the first year.

In the average 28-day cycle, the most fertile period is between days 10 and 16. This is the period around ovulation. The egg can be fertilized for up to 72 hours and sperm maintains its fertilizing capacity for 3-5 days. Therefore, unprotected intercourse is most likely to lead to pregnancy in the periovulatory period.

If pregnancy is not desired, a woman or her partner must choose from the available contraceptive methods. One option is to avoid the periovulatory period or to interrupt intercourse just prior to ejaculation. Chemicals can be used to immobilize the sperm, whereas barrier methods offer protection by blocking the sperm's access to the upper genital tract. Hormonal methods induce unfavorable cervical and endometrial changes and interfere with ovulation and tubal transport of the gametes. Intrauterine devices (IUDs) induce unfavorable endometrial changes, are toxic to sperm, and interfere with tubal transport of sperm and egg. Surgical methods block the ducts (fallopian tubes or ductus deferens) and prevent the gametes from having direct contact.

Contraceptive methods vary in their efficacy. Contraceptive efficacy can be expressed as failure rate with perfect use (all instructions followed all the time) or with typical use (the way most people use any given method, which includes days or occasions of imperfect use). This study summarizes the efficacy of various contraceptive methods.

Study Summary

Trussel's review encompasses the results of individual published surveys and studies. Failure rates (percentage of women with unintended pregnancy during the first year of use) are calculated for both perfect and typical use. Some of these rates are corrected on the basis of expected underreporting or overreporting of failure with a given contraceptive method. The failure rate of some methods is the same with perfect and with typical use (eg, Implanon® birth control implant), whereas the difference in failure rate between perfect and typical use of other methods is significant (eg, withdrawal). Surgical methods (tubal ligation, male sterilization), IUDs (copper IUD, progestin-releasing IUD), and progesterone implants provide the most effective contraception. The failure rate with these options is less than 1% with both perfect and typical use. Hormonal methods (pill, ring, patch, Depo-Provera®) are very effective when used perfectly (failure rate less than 1%), but with typical use the failure rate is estimated to be 6%-9%. The failure rate with barrier methods is in the 1%-24% range with typical use and in the 2%-20% range with perfect use. Calendar methods are associated with a 25% failure rate with typical use but can be quite effective when used perfectly (0.4%-5% failure rate). Spermicides provide the least effective contraception (28% failure rate with typical use and 18% failure rate with perfect use).

Discussion

Many considerations enter into the choice of a method for contraception. Age, parity, medical problems, desire for future fertility, duration of contraceptive use, noncontraceptive benefits, and compliance are all important. Ideally, a woman would choose to use a method that provides effective contraception for the desired interval, is easy to use, has minimal side effects, and potentially offers benefits beyond contraception. Women who have completed their families will likely choose permanent or long-term solutions (surgical methods, IUD, implants). Younger women who are not yet in stable relationships and who may have several partners over a period of time are more likely to use barrier methods that can be used occasionally and offer protection against sexually transmitted infections in addition to preventing pregnancy. Women in stable relationships who have not completed their families are likely to choose combined hormonal methods. Finally, women who for medical reasons (menorrhagia, dysmenorrhea, anemia, etc.) must use a certain method will likely choose the combined hormonal methods, Depo-Provera, or progestin IUD.

When making the decision, it is also important to assess how well the patient will comply with the required use. Not everyone is compliant with daily pill use and for this reason, these individuals may opt for an implant or Depo-Provera. Financial considerations also play a role in the selection process.

Last, but not least, contraceptive efficacy must be considered, and Trussel's review is very helpful in this respect. On the basis of reported failure rates, a woman can make an informed decision on which method will best suit her. Because half of all pregnancies are unintended and many will end in abortion, the widespread and proper use of effective contraceptive methods is desired to avoid the potentially challenging decision of pregnancy termination and its effects.[2]

Abstract

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