I definitely agree with getting x-rays - your vet should be able to tell the best time for them to be the most accurate. It is SOO important for so many reasons - mainly as stated above - this way you know how many puppies to expect. In addition, say you have a smaller mamma (4 - 5 lbs pre-pregnancy) and she is only carrying one to two puppies. Well, that would be almost a guarenteed c-section because the puppies are going to be bigger (6 - 7 oz each vs. 4 oz) which makes all the difference in passing through the birth canal. 3 puppies is just about perfect for a small mamma for natural birth, because more than three, and she could become so tired after the third that she just stops pushing, and then you have a problem delivering the 4th.
In addition, a good vet will be able to estimate more accurately when the puppies will be born - this is important for those whose mamma's got pregnant accidently.
