I recently got caught up on a certain medical drama series on Netflix - and finally realized what all the fuss was about- but noticed one particular plot device used far too often, especially considering that the characters all had medical training: the accidental pregnancy.

The two most popular methods of birth control, condoms and hormonal birth control ( like the birth control pill), are both highly effective. When used properly, these types of birth control are up to 98% effective.

What does this mean? It means that, if you are on the pill and having sex regularly and you never forgot or skip a pill, there's only a 2% chance - only 2 in 100 - that you will get pregnant within a year. This is not a 2% chance of failure each time you have sex. It's a much smaller risk of failure than that.

Most accidental pregnancies happen when people get sloppy with their birth control; they start a new pack of pills or put on a new patch a week or two late, they decide to go without a condom 'just this once,' they use birth control that is expired and has been stored in a hot glove compartment for months, they don't realize that some medications reduce the effectiveness of hormonal birth control, etc.

There are some people who do use their birth control properly and still wind up unexpectedly pregnant. Some kinds of pills have lower levels of active ingredients and are more prone to fail. And yes, condoms do (rarely) break and IUDs can be spontaneously passed from the body. But this is the exception, not the rule.

Some people have a hard time finding a method of birth control that they tolerate. Some women have intolerable side effects when they use hormonal birth control (like migraines or worsening of depression, especially in people who are already prone to these problems). Some people are allergic to the latex in condoms. However, this doesn't give them a free pass from their responsibilities when it comes to their reproductive health; they just have to work harder to find a method that works, and may have to resort to a less effective method of birth control, like a diaphragm or the fertility awareness method.

If your character is 100% sure that she doesn't want to get pregnant, then she must be 100% diligent with her birth control. If your character is the type who always wears her seatbelt and always brushes her teeth, there needs to be a very good story reason for her not to be using birth control properly if your plot depends on her getting pregnant.