With any handling once tupped there is a small risk of the stress causing metabolic problems, even abortion. So if you do feel they need worming and/or fluking, try to keep everything as calm and stress-free as possible.
Of course, if you think they need both, use a combined wormer + fluker so it's just one operation.
We normally do worm and/or fluke before tupping, then copper and minerals a month or so after, fluke again and their clostridial jabs about 2-4 weeks before lambing. When driving and handling pregnant ewes we take it very steady and try to minimise stress.
HTH