50 Great Myths of Human Sexuality by Martha Kempner

Author:Martha Kempner [Kempner, Martha]
Language: eng
Format: epub
ISBN: 9781118611203
Amazon: B00SOMZ50Q
Publisher: Wiley-Blackwell
Published: 2015-01-19T23:00:00+00:00

How Good Is Withdrawal at Preventing Pregnancy?

Our apologies as we have gone over this before, but we think it is very important that everyone understands how contraceptive effectiveness rates are calculated since this is the math that people use to make their own decisions about which methods to use.

It is difficult to calculate exact contraceptive efficacy because every couple has a different risk of pregnancy based on how fertile they are and how often they have sex. Researchers estimate how well contraceptive methods work based on clinical trials and other tests of the methods as well as studies that ask couples to recount when they had sex, what methods they used, and whether they had ever experienced an unintended pregnancy. These numbers are plugged into complicated equations and then each contraceptive method is given two efficacy rates: the perfect use rate refers to how well the method will work if used consistently and correctly such as in a controlled clinical trial, while the typical use rate refers to how well the method will work when used by a normal couple under real-life conditions (Trussell, 2011, p. 779).

Rates are expressed by showing how many couples out of 100 who use the method will experience an unintended pregnancy in the first 12 months. The perfect use rate for condoms, for example, is 98% because when used consistently and correctly only 2 out of 100 couples will experience an unintended pregnancy in the first year. Put another way, under perfect conditions condoms only fail to prevent pregnancy 2% of the time. Other methods like IUDs have even higher perfect use rates—over 99% (Trussell, p. 784).

For most methods, typical use rates are lower because human error enters the picture. The typical use rate for condoms is 82% because 18 out of 100 typical couples who say they use condoms as their primary method of birth control will experience an unintended pregnancy during the first year of use. This includes couples who were not using condoms correctly when they became pregnant. It also includes couples who were not using condoms at all when they became pregnant (Trussell, p. 784). Methods like IUDs have typical use rates that are almost identical to perfect use rates because once they are properly inserted by a health care provider they work—without the user having to doing anything to ensure that they work and without the chance of the user doing anything to interfere with how they work.

When looking at the numbers, withdrawal compares favorably to other methods. There is some debate about the exact efficacy rates of withdrawal, but it is generally accepted that it can be 96% effective with perfect use. The 20th edition of Contraceptive Technology cites the typical use rates as 78% but other research says it is closer to 82% (Jones et al., 2009).

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