"Generally you shouldn't use medicines in pregnant cats, so I don't recommend deworming during pregnancy - there's always a risk involved. On the other hand, NOT deworming is likely to have serious effects on mom and kittens. Mother cats with intestinal worms can pass worms on to the kittens through the womb (and later milk).

Some deworming products are safe to use in pregnant cats up to two weeks before birth. Usually this is mentioned in the product description. So... Treatment does not have to be harmful, but it depends on the product and the stage of pregnancy."

taken from another site. As for vacination, if you do know the side effect it will do to cats or kittens, you would think twice of doing it. Maybe ending up killing both parties. Just my oppinion

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Save stray cats to show that you care. Not to say that you cant afford a good breed, but to show you are doing a good deed.