Before taking my advice, CALL THE VET and ask them if it is ok.
We found out, surprisingly, a human shampoo kills fleas on contact. We ran out of dog shampoo one weekend and washed our dog in Tressemme (the big black bottle). We noticed the fleas washed off and did not move. It did not stun them. It killed them. Since then, we have used it as the 1st wash, then used his regular oatmeal dog shampoo as the 2nd wash. He has never had any reactions from Tressemme. He is a large breed husky mutt.
Again, PLEASE call the vet before using this on a pregnant dog.