Yes, it is possible for you to get pregnant on birth control, but the chances are very slim. According to some experts, the chance is only one out of every 1,000 women. This only applies to women who use the medication exactly as instructed. If you miss a dose for any reason, the chances you can get pregnant on birth control go up drastically, and each additional dose missed after that increases the chances more. If there is any mistake at all in the way you take the medication, the pill may not work properly.
There are many cases of women getting pregnant on birth control, but experts believe the vast majority of them involve accidental misuse of the medication. It is relatively easy for this to happen. For example, women can increase the chances of pregnancy by simply using the pill at the wrong time of day.
Most birth control medications work primarily by stopping the woman from ovulating. This basically short-circuits the whole pregnancy process, so the pill is usually very effective. If the pill doesn't work, it is generally because of a failure to halt ovulation. Sometimes a woman may become pregnant on birth control after a failure caused by some unexpected factor, such as a bad interaction with some other medication she is taking. At other times, the reasons for a birth control failure may be generally unclear.
People’s memories aren’t generally perfect, and they may not realize they missed a dose. When taking the same medication every day at exactly the same time, a person can become confused about the timing of their last dose. They may remember taking a pill, but the memory may be from a different day. It’s usually possible to check and see if the memory is accurate, but in the heat of the moment, people may simply trust their minds, especially if they feel relatively confident about what they're remembering.
As a way to guard against the imperfections of memory, some women choose to rely on some other contraception method as a backup. For example, a woman may also insist that her partner wear a condom, or she may use some kind of spermicide gel. These methods aren’t perfect either, but when used in combination with birth control pills, they can often be enough to compensate for any errors in judgment or memory.