Choosing a Birth Control Method

Part Two: How Well Does YOUR Birth Control Work?

How Well Does YOUR Birth Control Work?

Rachel Flink, MD

People have been trying to control family size throughout history, but with the advent of modern contraception, it’s become easier and easier to plan pregnancies.  This is because modern methods, in addition to being safer, are more effective than many methods used previously.  This factor may matter different amounts to different people.  If a woman knows she does not want to become pregnant for a certain time and she feels it is very important to delay pregnancy until that time, then effectiveness may be a critical factor in her decision about birth control options.  If a woman would ideally like to delay pregnancy but would not be upset if it happened sooner, or if she and her partner would welcome a pregnancy, but don’t feel comfortable actively planning for it, then effectiveness may be less important or even a deterrent to using a certain method.  (As a side note, if there is a reasonable chance of pregnancy, women should optimize other health factors, such as control of chronic conditions, prenatal vitamin use, achieving a healthy weight, and cessation of smoking and substance use.)

Before launching into particulars, let’s discuss how to interpret effectiveness and failure rates.  In a typical year, a woman who is having regular unprotected intercourse has an 85% chance of getting pregnant, meaning that 85 out of 100 women will become pregnant in a year.  This translates to about a 30-35% chance each menstrual cycle for a woman in her twenties.  Younger women have an even higher chance of pregnancy, and older women have a lower chance.  When people talk about effectiveness of birth control, they can refer to “perfect use,” which is under ideal research conditions, or “typical use,” which refers to how effective birth control is under real world conditions.  Failure rates are the opposite of effectiveness and are easier to understand – they’re the chance of getting pregnant in a given year of using a contraceptive method.  All of these should be compared to the 85% “failure rate” of using no method at all.  

As far as the particular birth control methods available, effectiveness tends to go hand-in-hand with ease of use, with the easiest methods to use being the most effective.  Most people know that tubal ligation is extremely effective, requiring a quick outpatient surgery and having failure rates less than 1%, meaning that fewer than 1 in 100 women will get pregnant each year.  For those women who don’t want to close the door on childbearing, or who don’t want surgery, long-acting reversible contraceptives (LARC), like intrauterine devices (IUDs) and implants, are just as effective if not more, with fewer than 1% of users each year having an unintended pregnancy (sometimes much fewer).  LARC also tends to be safer, avoiding the need for surgery, and can last for 3 years (Nexplanon® implant, Skyla® IUD), 5 years (Mirena® and Liletta® IUDs) or 10-12 years (copper IUD), with a quick doctor’s office visit for placement and removal.  

Other options require more frequent dosing and have higher failure rates.  Injectable contraception (Depo Provera) requires an office visit every 3 months for administration with a 6% failure rate each year.   The vaginal ring (NuvaRing®) needs to be changed every 3-4 weeks.  The birth control patch (OrthoEvra, Xulane) needs to be changed every week.  Birth control pills need to be taken every day at the same time. Pills, patches and the ring all need prescription refills every 1-3 months and have failure rates of 9% each year.  

Barrier methods, like condoms and withdrawal, need to be used every single time a woman has intercourse, and have failure rates of 15-25% each year, although they have the benefit of not requiring visits to a doctor’s office.  Fertility awareness or natural family planning involves monitoring of body temperature, vaginal secretions, urinary hormones and/or other cycle factors, and requires abstinence or condom use for around half of each cycle, with various amounts of training needed to understand and use the method properly.  Fertility awareness-based methods have failure rates of 10-25% each year, depending on the method, the woman’s natural cycles, and commitment by both partners.

As mentioned earlier, effectiveness is an important component of choosing a birth control method, but each woman has different goals, which should be discussed with their doctor or other health care provider.  The next post will discuss the side effects of different birth control options, which is the other major factor most people use to make their decisions about birth control.  


Rachel Flink, MD is an OB/GYN currently practicing in Western Pennsylvania and obtaining her Masters in Public Health at the University of Pittsburgh.  Her clinical interests include reproductive health, pregnancy care, family planning, and minimizing barriers to care.  Rachel’s research is focused on understanding women’s experiences with and preferences for reproductive health care.  Outside of work, she enjoys reading, being active outdoors, and spending time with her husband, two-year-old son, and rambunctious dog.

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