Cristiana the cord thing is my personal obsession, but even I've had to give it up now. I'm pretty sure I read the same story mentioned by nationalfight, but in that case, if you read into it, they had been on the alert because there was something wrong with the cord, so it was already high risk. Nearly all cords are equipped to avoid any damage to the baby in the womb from this, and if they're not, this is generally picked up in the scan.
Also, remember your baby does not breathe through its nose and mouth yet - you're breathing for him/her!