can your dog get pregnant on the first week of heat?
Generally, I'd say no...if by chance you missed the first couple of days, tho...her second week maybe upon you before you know it. The first week of heat, is when the uterus is getting ready (thickening, swelling with blood, etc)...to take on pups...it's also the time you'll see her flirting with males, and "gathering" her suitors...
not usually until the second week, but I wouldn't be completely rule out that they can't get pregnant during the first week. it's possible. watch her carefully and keep her away from any male dogs that aren't fixed.