What do you tell people why you’re not drinking?

I have been TTC for 2.5 years and stopped drinking to give me the best possible chance. Because of this I often cancel plans, stay home as it’s easier than trying to think of an excuse of why I’m not drinking. Now Christmas is coming up, I have my annual Christmas party with family to attend and I have no idea what to tell people on why I am not drinking. I don’t want to tell them the truth as it’s just too much pressure when more people find out about my TTC journey. Any advice on what I can tell people?