**DISCLAIMER**We've never had eclampsia, and more importantly, I'm not a veterinarian, canine nutrition expert or any kind of expert other than a very interested hobbyist.**END OF DISCLAIMER**
There IS an alternative to feeding puppy food to a pregnant bitch. There are alot of issues around this that I just don't want to get into, but we don't even feed puppy food to puppies. It's too rich, has added calcium, etc.
So, here's the alternative. We feed a raw food diet that includes raw meaty bones (in our case chicken wings). The problem with calcium supplementation is that it is absorbed and utilized differently in the body from a whole food source. (Reminder, refer to my first paragraph, folks, this is strictly my opinion.) Our girl eats her normal ground raw food diet and chicken wings until she whelps, then she's offered a goat's milk mixture with raw egg and honey and flax seed oil and I can't remember what else. She gets all she wants. Other than the fact that it can leave some nasty white scum on her teeth and it smells bad after a day or two on your bath robe, this has worked beautifully.
Obviously, this method is not for the faint of heart. I watched my first Yorkie eat a chicken wing with the Emergency Vet phone number and my car keys in my hands. Turns out they do just fine.
I'm not promoting this type of diet. We fed premium commercial dog food for many years. We don't require new puppy owners to feed raw. It's not for everyone. I also wouldn't switch a bitch who has had eclampsia before to this diet and expect to be problem free. But, again in my opinion, if you want THE BEST for your girl and you want to be free of whelping problems, it's worth a shot.
CJ