Tuesday, April 10, 2007

Birth Control: A Condom Isn't Enough

If you have regular intercourse for 3 years using only a condom for protection, you have a 36% chance of getting pregnant.

( . . . pause for reflection . . . )

Using the pill instead of the condom is a bit better with a 14.3% chance of pregnancy over three years. Using them both brings the chances down to 5% over three years, which is why my mom once told me to "always use two forms of birth control". Even a 5% chance isn't something to take lightly considering the consequences.

There are two main things which can lower the risk of pregnancy:

1) Make sure you use the condom or pill as directed. For those using a condom alone, perfect use lowers the 3-year risk from 36% to 9%. Of course, nobody's perfect.

2) Use a method that doesn't require user intervention: the hormone shot or implant. Those have a 3-year risk of less than 1% on their own and even less when used in addition to a condom.

Here are some details:

Chances of getting pregnant during one year of sexual activity

MethodRate of Pregnancy
(Typical Use)
Rate of Pregnancy
(Perfect Use)

Implant (Norplant)0.09%0.09%
Hormone Shot (Depo-Provera)0.3%0.3%
Combined Pill (Estrogen/Progestin)5% 0.1%
Male Latex Condom14%3%
No Method:85%85%

Chances of getting pregnant during three years of sexual activity

MethodRate of Pregnancy
(Typical Use)
Rate of Pregnancy
(Perfect Use)

Implant (Norplant)0.27%0.27%
Hormone Shot (Depo-Provera)0.9%0.9%
Combined Pill (Estrogen/Progestin)14.3% 3%
Male Latex Condom36.4%9%
No Method:99.7%99.7%

(click here for the full table of all birth control methods)


dave hiller said...

I would really like to see the original data, but the FDA doesn't link to it anywhere as far as I can tell (except a reference to a text that is in press).

The pill is listed as having the same success rate as sterilization, if used perfectly. This makes me wonder what the baseline is. Also, it's curious that withdrawal is just barely worse than a condom (4% vs 3% with "perfect use"). Huh? I guess maybe now my intuition is off, but I'd like to see how they came up with these numbers.

dave hiller said...

Ok, I've done some more reading (hopefully no one was looking over my shoulder at work). It seems that there is a huge distinction between "perfect" and "typical" use, which may be understated in the FDA article. Here are a few reasons why a condom might fail due to user error: putting it on too late, putting it on wrong, using an oil-based lubricant, not being careful during withdrawal, or not putting it on at all. (See discussion of method vs user failure here.) That's right, if a condom is your primary method of birth control and you skip using one, that counts in the "typical" statistic. Typically stupid?

The most optimistic study I found looked at the rates of condom failure in Nevada brothels. Out of 353 acts of intercourse, the condom never broke and never slipped off, though it did sometimes slip down. This indicates that user error is really the dominant factor, and with practice you can reduce the risk quite substantially. :) So, when you use a condom, use it correctly.

That being said, I still probably wouldn't use it as my primary form of birth control. I think the pill is also quite a bit better than listed by the FDA, if taken every day. However, for men a condom is the only thing you have control over, so unless you're in a relationship where you know whether the woman is taking a pill every day (and you know they don't have any STDs, which a condom is very effective against), it's your only choice.

Alan Rosenwinkel said...

Yes. If you use a condom perfectly, your chances of getting someone pregnant go down a lot; however, don't be a casualty of the Lake Wobegon effect. 80% of people believe they are in the top 30% of drivers. Likewise, most people probably think they use the condom correctly, but often don't. So, BE CAREFUL! Use your condom correctly!!!

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