I kind of can't believe I'm asking this in an online forum....but I need underwear help!

I'm Wearing a very fitted (but stretchy) dress to a wedding in a few weeks.. I'll be 17 wks pregnant and thus far don't have much of a bump (the fitted dress is an attempt to actually look pregnant and not just like I've put on weight). The fabric of the dress will show any line (I don't even think a Hanky Panky thong would really work), so I'm wondering if it is a terrible idea to wear Spanx? Or does anyone have another suggestion? Thanks in advance!