Pregnacare would have been very thoroughly tested and trialled to make sure the doses of vitamins are not harmful to the baby. Sure, folic acid is for the baby, but as Jasmine said the rest of the vitamins are aimed at keeping Mum healthy.
You could try and encompass all of the vitamin doses in pregnacare into your diet, in which case no-one would suggest you're doing anything remotely harmful or unnecessary but in reality, especially in the early days when you become averse to so many foods it would be near impossible to do.
I know big doses of some vitamins can have negative effects, but they are very very big doses - not just what you'd find in a multi-vitamin tablet.
With vitamin C for example, you can OD, but you'd have to be taking a supplement and eating 40 oranges before that would happen!