Personal choice, agree with the poster above who mentioned being in a stable, commited relationship. If you are settled with your partner, I honestly don't believe that the marriage certificate suddenly makes a whole lot of difference.
I got married when I was five months pregnant, we just thought, let's do it. Close family and longtime friends only, registry office then meal. There again, we aren't big wedding or occasion type people, so it suited us and just seemed like an opportune time to get married.
I wouldn't say that we got married because I was pregnant, we had lived together for a time, it just seemed like as good a time as any.