I'm paranoid I've got a big belly already, but the timing of a weeks holiday eating loads hasn't helped!!
In early pregnancy, rather than buying loads trs, try buying waist expander thing. It comes in a pack of blue, black and white material with elastic button/clips on, so you can wear you current trs with the fly open, but the elastic and material keeps the trs up and covers the fly area - only about ??15! Well worth it, I found this out too late last time, having spent loads on maternity work trs!!
P.S.Next sale is on, there are a few maternity bits on there looking at!
Mrs RF