That's a picture of my roommates chi before she had Vida and the other babies! I really don't know how much weight she gained but she got BIG!!! she did have 4 pups 2 born right way 2 born backwards one died (one of them born backwards) the other one that was born backwards my roommate had to gently help her pull. Also the sac they are born in had to be popped and opened (they come out individually rapped like Twinkies lol) it's very good that you are involving your vet so closely. If you have any other questions I'd be happy to try to answer them
Also Lush herself is about 5lbs (Vida's mom shown here) and the father was at least 7lbs Vida was 1st born and took after him being a bit bigger in size we were very lucky to have been blessed with a successful natural birth of 3 wonderful chi although it was very sad knowing one of the chi died because it came out wrong and wasn't able to do anything as it died...
I would suggest you talk to your vet about what they can do if they are born backwards or if any complications happen that may put your chi at risk. Make sure you post TONS of pixs of her growing belly!
It's a gross experience but witnessing the moment of birth of my adorable baby is a memory I will always have forever lol ...also watching a chi go from being the playful and silly chi to being a responsible mother is also an amazing moment! hope you record it too! I wish I had :S