When I was pg with DD I was only 10 or 11 weeks and hadn't told anyone yet, well my family and close friends knew.
I made a brief appearance but was so tired we went home.

I was 6months pg with DS on New Years so I stayed at home, couldn't be bothered with it all.

If know one knows yet, maybe get you partner to act sick as well and go on how you are both not feeling well and go home. The easiest way would be too stay at home, you wouldn't have to deal with anyone or stress about being sick, fainting etc.