I put on about 18kg with my twins and wore the same maternity clothes the whole way through as it was only my belly that got bigger. I just bought the clothes with the adjustable buttons inside the waist band and made sure that the legs and bum were a little lose. Tops got a little short towards the end but I just wore a belly band or singlet top underneath.
For home I had some maternity pants i got from bigw that were 3/4's and a bit like yoga pants. They had a roll down waist and were sooooo comfy especially towards the end when i was really big. They were great for in hospital after the birth as they were soft on my c-section cut. I also had a dress (or should I say tent) that was loose that I wore at home when we had no visitors as it was more comfy towards the end (didnt wear it in public as it looked hideous).
I bought some stuff at about 16 weeks and then a little bit more at 26 weeks and that lasted me until 37 weeks. I found undies the hardest things to get as one baby was down so low and breech that even hipsters would roll down. .

Hope this helped a bit.

Andie

It's something very hard to advise on. I put on 30kgs with my twins, and 28 with my last singelton baby So you see just because you are carryins twins does not mean you will get huge. As you can see from an above poster she only gained 18kgs, still 6kgs less than what I gained with my first singelton (24kgs).

I tended to shop in the "Big Ladies" section at the stores, much cheaper than anything with the word Maternity attached hehe Kmart is great for having awesome sales, I got one skirt that I wore to death for only $6