I think that making the comment about her boyfriend in the first place was stupid. You could have just kept your mouth shut and saved the whole ordeal from happening.
A girl in my grade got pregnant last year, and it was REALLY hard for her. She kept the baby, and she's graduating, but she's worked really hard to do that. We have the same name (we're the only two Alisha's in the grade), and when the rumour first started going around the school, and people first found out that she was pregant (before she started to show), a lot of people mistook me for her (they'd just heard things like 'That grade 11 girl, Alisha, is pregant...' etc), and some of their comments weren't that nice. I really respect her for going through what she did and facing up to her responsibilities.
Condoms don't always work, and mistakes can happen for people on the pill. If the girl you're talking about didn't use any protection, than that was her mistake, but that doesn't make it any of your business.
Tripping a pregnant girl, no matter how far along she is, is a horrible thing to do.
'Seduce my mind, and you can have my body. Find my soul, and I'm yours forever.'