When Can Birth Control Fail?

No form of contraception is perfect, so there is always a chance that you could get pregnant if you have sex when you are fertile (usually during the middle of your menstrual cycle). However, modern contraceptives can be more than 99% effective when they are working properly. Why does birth control fail and is there anything you can do to reduce the risk?

Unavoidable Contraception Failures

The first reason why birth control can fail is that there is no contraception than can prevent 100% of pregnancies. Each form of contraception has an effectiveness rate that tells you how reliable it is. An effectiveness rate of 90% tells you that for every 100 people who use that contraception for a year, 10 of them would get pregnant.

You should make sure that you know what this rate is when you choose your contraception, as it can vary quite widely. It’s also important to be aware that the effectiveness of a contraceptive with typical use (how the average person uses it) than with perfect use.

For example:

• The pill is more than 99% effective when used perfectly, but for the typical user it is about 91%. If you often forget to take your pill, it could be even lower.
• A contraceptive implant, IUS or IUD is more than 99% effective, even with typical use as you don’t need to do anything to keep it working
• Natural family planning apps can be more than 90% effective with perfect use, but are only about 76% effective for the average user
• Condoms are 98% effective with perfect use and 82% effective with typical use, but they are the only form of contraception that can protect against STIs

Avoidable Contraception Failures

The typical use rates reveal the second reason why birth control may fail: people make mistakes. We don’t always use our contraceptives perfectly and things can sometimes go wrong.

Some of the most common mistakes that people make with birth control include:

• Forgetting to take the birth control pill at the same time every day, or not realising that it won’t work properly when taking certain medications or after being sick.
• Not using a condom correctly, for example by using the wrong size or putting it on incorrectly so that it splits or slips off. Failing to put the condom on early enough or taking it off too close to your partner can also cause problems, as can oil-based lubricants that degrade the condom.
• Not reading, understanding or following the instructions can reduce the effectiveness of all types of contraception. It’s important to take the time to do this and to ask for contraception advice from your doctor if you’re unsure about anything.

Using contraception is the best way to prevent an unplanned pregnancy, but it’s important to be aware of the limitations. Since contraceptives can be as low as 70% effective with typical use, it’s not surprising that around half of the women who seek abortions in the UK were using at least one form of contraception. Ensuring that you choose the right contraceptive, using it correctly, and combining contraceptives can all help to reduce the risks that your birth control will fail.