Maternity bras should have a little bit of give in the cup so when your milk comes in, they will still fit. That means that they are not loose on you now, they will fit perfectly but the cup will be stretchy to allow for growth.

With DS I went from a C cup to a D cup and stayed there. This time in pregnancy I have gone from a D cup to a DD. Personally, I prefer to buy maternity bras during pregnancy as I will use them when baby is born until they fall apart rather than buy regular non-underwire and not be able to use them for bf'ing.

I also prefer the soft cup bras because they contour your boobs better so once your milk settles down, you don't have gaping at the top of the cup. I found that the firmer cups gape once the milk settles down.