Choosing Contraception Based on Effectiveness

By Aaron Hamlin | November 7, 2014

You may have heard that the male condom has a 2 percent failure rate. But do you know what that means?

Failure rate, as it turns out, has nothing to do with a condom breaking or slipping off. Instead, it refers to the number of times a pregnancy occurs — regardless of whether that pregnancy results in birth, a miscarriage or abortion.

The confusion over what failure rate means is why academics use the term pregnancy rate. (And it’s why this article will use the term pregnancy rate from here on, too.)

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The most reliable data on pregnancy rates come from using the National Survey on Family Growth (NSFG). This large-scale survey asked more than 7,000 women ages 15 to 44 about the contraceptive they were using and whether they experienced a pregnancy. Respondents noted when they started using a particular method (though it wasn’t necessarily the first time they ever used that method), and the pregnancy rates were then converted into one-year periods.

So, it’s correct to say that if you’re using a condom, the probability of becoming pregnant, over the course of one year, is 2 percent.

But that’s not all: The condom’s 2 percent pregnancy rate refers to its perfect-use rate. And we’re not all perfect.

What’s Typical?

Contraceptive pregnancy rates are separated out into two categories: “typical use” and “perfect use.”

Typical use is what happens in real life, and it’s the average among everyone: Forgot to use the condom? Didn’t put it on right? Used it correctly and consistently? It all counts toward typical use.

Perfect use refers only to those instances where the contraceptive method is used consistently and correctly each and every time. Sometimes, however, it’s hard for researchers to get good data on perfect-use rates, so they do their best to give good estimates based on the information they have.

The difference between typical and perfect-use pregnancy rates is huge. The typical (real world) pregnancy rate for condoms, after one year, is 18 percent — nine times higher than the perfect-use pregnancy rate of 2 percent.

We see this rate discrepancy not only with condoms but with all contraceptive methods that allow for user error. Take the pill, the most popular form of contraception in the United States. Its perfect-use pregnancy rate is only 0.3 percent, while its typical-use rate is 9 percent.

For contrast, look at the pregnancy rates for for long-acting reversible contraception (LARC) methods. For example, a hormonal implant inserted under the skin of a woman’s upper arm (under the brand names Implanon or Nexplanon), has a perfect-use pregnancy rate of 0.05 percent — as good as contraceptives get. Its typical-use rate? Also 0.05 percent.

The same goes for a hormonal intrauterine device (IUD), such as Mirena, that releases a small amount of progestin each day. Its perfect- and typical-use rates are both 0.2 percent. That’s because these methods shrink typical-use pregnancy rates by either minimizing or eliminating the possibility for user error.

Click here to enlarge the chart below
Source: Centers for Disease Control and Prevention

CDC chart showing effectiveness of contraceptive methods

What does this mean to You?

The NSFG survey refers to a large sample of people meant to represent the population at large. While it would be incorrect to extrapolate that information to the individual level — like to you — it’s hard for pregnancy rates to be useful otherwise.

So here it goes: When you’re considering which type of contraception to use, it’s helpful to look at the typical-use rate. Then, try to be honest with yourself and decide whether you should move closer to the perfect-use rate or further away.

It might also help to look at pregnancy rates beyond one year — after all, we’re not limited to one year of sex. Unfortunately, we don’t have good data on long-term pregnancy rates, but we can get an idea of what happens over longer periods of time.

Let’s say you’re an average condom user, and your odds of experiencing a pregnancy in one year are 18 percent. But you aspire to be a better user (good for you!). Over the next five years, you follow through, using a condom more consistently and correctly each year. As an improving condom user, you lower your pregnancy risk by 4 percent each year until you hit the perfect-use pregnancy rate of 2 percent — 18 percent rate the first year, then 14 percent, then 10 percent, then 6 percent, then 2 percent.

Over this five-year span, the risk of encountering at least one pregnancy — even though you’re improving usage each year — is just over 40 percent.

Dealing with the Numbers

This 40 percent risk explains why half of women between the ages of 15 and 44 in the United States experienced an unplanned pregnancy.

Note that 90 percent of women at risk for an unplanned pregnancy really do use contraception. And while the majority of contraceptive users aren’t perfect, even perfect users still account for 5 percent of unplanned pregnancies.

What can you do to reduce your numbers? It’s easy to just say that you should become a perfect user. That will certainly make a big difference, but it’s not a realistic option for everyone.

Using more effective methods is one approach. As mentioned, a long-acting reversible contraceptive, such as an implant or IUD, has a great pregnancy-rate track record. Further, more than 75 percent of users keep using those methods after a year. That’s a better continuing-use rate than condoms or the pill.

Let’s say both you and your partner are not perfect users, and long-acting methods are not an option. Another route is to use at least two methods simultaneously, an approach taken by 15 percent of men and women. By using two methods simultaneously, both methods have to fail at the same time in order for pregnancy to occur.

The most common example would be using the pill and condom together. But you could do other combinations, such as the pill and withdrawal, condom and rhythm method, or diaphragm and the pill. Any combination will be better than using one of the methods alone, though the lack of contraceptive options for men limits the combinations.

This is yet another reason why we need more contraceptive options — especially for men. With a better understanding of how pregnancy rates work, we can make better decisions for ourselves. And we can make more intelligent demands for new contraceptives.