
I agree with the advice already given. I have used Panacur 10% for many years, from day 40 to 2 days post whelp. Other makes that give less dosing, are not tiny doses like Panacur. Remember that, although given daily, it is only 25% of a normal adult dose. It works a treat on those encysted worms, and your pups will be born 98% worm free. I wouldn't wait until puppies are born.
If you Panacur mum, all pups will have to do is go ahead and thrive (as opposed to carrying a heavy worm burden.)
Not worming at all until after pups are born is not an option for me.