OK, it's not actually a miracle. But I found it helps in early pregnancy when you're swelling, but not big enough to have maternity clothes.
I got the "Belly Band Combo Kit" from Mothercare in Prince's Bldg (HK $160). You have to ask for it -- the saleslady didn't really know what it was.
It's a series of tiny belts in different lengths -- some with buttons, some with clapses -- that you latch onto your jeans, trousers or skirts. The smallest setting expands a waistline about 1". That's what I'm using now -- it makes it more comfortable when I'm sitting 8 hours in an office. It also avoids suspicious bunching -- I don't want colleagues to know yet.
The longest expands the waist by 5" and has a "modesty panel" so it doesn't look like your fly is hugely open. :) In any case, I pair it with a long, loose top.
BTW, if my baby is the size of a peanut or something, why am I already so swollen?