It varies just the same as a singleton pregnancy. I started getting bloated right off the bat and had to wear maternity bottoms from 12 weeks on. But, I started getting an actually bump around 16 weeks (one that me and close friends/relatives could notice). Strangers still couldn't tell at that point. It was about 18/19 weeks or so that strangers could tell. And now I'm HUGE! lol. Once it starts to grow, it grows fast!