Me and my girlfriend had sex 3 days before her period, we used a condom but it popped, after we had sex she never had her period, she is now 12 days late... could she be pregnant?

If you have sex, protected or not there is always a chance of pregnancy. Nothing but abstinence is 100% Time to purchase a Home Pregnancy Test. May I ask how old you are?

I'm 18. Is it possible for her to get pregnant that fast and for her period to stop that quick? I mean it was only 3 days before her period but she never had it.

Yes, that is how it works.

Yep, Fr_Chuck pretty much summed it up. That's how pregnancy works. It really doesn't matter WHEN on her cycle you have sex, if you have sex, there's a chance you can get pregnant. Of course there are more fertile days than others, and J_9 can correct me if I am wrong, but I am fairly certain you are most fertile 12-14 days BEFORE your period. If the sperm met the egg, then nope she sure wouldn't have a period, because she would be pregnant.

It is also possible that her period is off from the sex right before she was due to start. She may have miscalculated when her period was due, she may have irregular cycles, her period may just be off, which can sometimes happen.

Certainly she should try a pregnancy test.

While it can happen, it would be unusual for her to become pregnant from sex three days before her period.

As Aurora_Bell stated, most women will ovulate about 12-16 days before a period is due. Some will a bit sooner, some a bit later.

If she did not ovulate within several days of the sex, she could not become pregnant... the sperm would not survive and there would be no egg available to fertilize.

If she tries a pregnancy test, and it is negative, she should wait and see what happens when her next period would be expected.

If you are going to continue engaging in sex, it would be wise for her to also use a form of birth control along with your use of a condom.

Important to keep in mind that pregnancy would still be a possibility. Give some thought as to how ready the two of you would be for the possibility of an unplanned pregnancy at this stage of your lives.