i can understand the point of private (but a public establishment) business and refuse service.... BUT on the other hand it was discrimination.
if it was a restaurant that requires formal attire and you show up in bluejeans and a metallica tee-shirt they can tell you to leave. but if you are pregnant/black/disabled and show up in formal attire they cant ask you to leave because you are pregnant/black/disabled simply because you one or all of those things. the bouncer clearly stated that she had to leave because she was preggers and that is flat out discrimination.
Discrimination is not a crime to let you know unless it is against a federal protected category. Pregnancy is not a federally protected category last time I checked.
As far as what can occur to the bar in terms of liability, one would be if she were to somehow obtain alcohol even if not served, and consumed it on their premises. They could be liable for that. Meaning if she went in, asked for alcohol, was refused, but someone else at the bar ordered something which caused problems with her baby, then they could be held liable. By refusing admittance, there is no chance of that happening.
I also believe in the right of an establishment to refuse service to anyone they choose not to so long as it isn't against the federally protected categories.
*EDIT* Here's the link to federally protected classes/categories
http://en.wikipedia.org/wiki/Protected_class
Pregnancy is not one of them. Familial status is one, but that one has a limited scope. That one deals specifically with housing laws only.
Also, they are not refusing entry to people with kids, or without kids, they are refusing based on a temporary condition to a single individual. No different than a work environment preventing an employee from working while contagiously ill.