
I wouldn't worm a bitch that had just been mated. She isn't going to be bothered by worms until pregnancy hormones kick in.
The only wormer licensed to use on pregnant bitches is Panacur suspension. The bitch isn't dosed until day 40 of pregnancy, and every day after until 2 days post whelp.
Using this regime, I have never had worms in mum or pups.
Oh - and I wouldn't buy from the vet when you can buy at half the price online and get free delivery! :-)