highly unlikely condoms have never let me down, im pregnant at the moment but it was planned, just put them on properly make sure they are covered in lube and not passed there expirey date!
I've used condoms as one birth control option off and on for 7 years. I've had at least one very early miscarriage and several broken condom scares, one of which was definitely while I was ovulating. And we buy the good ones. I'm presently 7 weeks with what we can only conclude is the result of a freak leaky or slipped condom, as none broke during that time frame, that we noticed. It was a total surprise.
In general, if you buy a high-quality condom, use it only once, and use it properly, it's not considered very likely that you'll get pregnant from using condoms as your only form of birth control -- odds are around 3%. If you're using no birth control at all, your partner ejaculates inside and you're ovulating or close to it, your chances of getting pregnant from a single encounter are roughly 20-25%, or about 7-8 times your chances of getting preggers from a condom whoops.
My first pregnancy I was on the pill and used condoms, after 3 years I got pregnant while using these. I'm not sure how likely it is but I think it was just a freak thing that I ended up pregnant.