I beleive that only Panacur wormer is licensed for use in Pregnancy.
I have wormed four generations of bitches this way now, starting tfrom 6 weeks in whelp (pups are now fully formed and past the absorbtion stage, just filling out) to 3 days post whelping.
I then worm at 3 weeks over 3 days, and again at 7 weeks (so they are finished before going to new homes. I then tell new owners to do them at 12 weeks and monthly until six months. I use the 10% suspension, and have only ever had problems with the one litter that I did sat 2 1/2, 5 and 8 weeks. As I had previously been told by vet when to worm I wey should have resulted in 98% worm free pups at birth.
This means I have wormed 8 litters without a hitch, with just my third litter causing me a lot of trouble with diarhoe, as to my mind thre times in 5 weeks is too often if th3e bitch has been wormed in whelp also.
I have never ever seen any worms passed, as I understqand that it disolves them.
A friend recently rescued a litter of 6 week GSD pups, and they were so full of worms that they did pass whole live and dead worms, and were aneamic too. This proved to me that a good worming protocol for ones dogs, especially breeding bitches is most important. The poor wee mites had no appetite, and weighed only 6 and a haldf pounds at 6 weeks. Now at 11 weeks one of the boys weighs in at 24 pounds! One little bitch was very ill with them, and is behind the others, and will problaqy stay small.