Hiya Hayleyjhay,
I've been taking pregnacare which contains 400mg of folic acid as well as other vitamins reccommended for pregnancy...
I also take folic acid (400mg) on its own but not the two together! I've had to do alternate days with the two as the pregnacare has iron in and its making me constipated (sorry)
But you can also get folic acid from foods such as cereal, brown bread and green veg - which i eat a lot of all three)
As for taking it all throughout the pregnancy i dont see why not take the supplement as its vitamins etc and its also good to take it whilst breast feeding....
If your really unsure ask your MW to clear things up for you
