What happens if you continue to take anticonceptive pills after becoming pregnant?

You need to talk to your doctor. Taking anti contraceptives while being pregnant is so dangerous for the child. See if there’s any harm to the baby, if not, it’s a lucky break.

yes, there is an increased rate of birth defects, and there is a higher chance for miscarriage

A lot of women unknowingly get pregnant while on birth control, and continue to take it. Just like taking the morning after pill will not abort a baby if it’s already implanting…birth control won’t cause a miscarriage. I am not sure on the specifics, I’d wait for @magsrags but I don’t think birth defects are an issue if it’s something like the pill.
But, for things like the depo shot, they get very concerned.

@Oxymoron, im not a girl xD

I wouldn’t call three weeks an “extended period of time”. Most women have no idea they’re pregnant until three weeks after conception. It’s not a big deal if they’re still taking the pill until they find out the pill has failed.

Now, taking hormone pills for an extended period of time (say, several months) there is a chance of birth defects, as @Violet suggested.

At one time, we did think there was an increased risk of birth defects if you used hormonal contraception in early pregnancy, but that turned out not to be true, thank goodness. Here’s a source from managingcontraception dot com, a reliable website that answers questions from consumers as well as care providers.

There was a 1991 study that showed increased risk of low bith weight for babies conceived within a month of getting a depo provera shot. But still, no birth defects.

Hooray! In that case, forget about the last paragraph of my answer. ^_^