Congratulations on your upcoming litter!
I think every female is different and pregnancies are always unpredictable
you can never tell for sure whats coming up....is just like a surprise box.
You can try to guess and xrays are a great tool to find out size and quantity but sometimes they turned way off
My female that is expecting right now, she is on day 59 and has gained 2.5 pounds , we'll see in the next few days , how everything turns out.
*They tend to gain weight on the last weeks of preg. so your girl may just start to get more weight next.