Excuses for not drinking?

Sarah
Just found out we're pregnant and heading into the holiday season.  Don't want to tell the in laws for a while longer (probably Christmas, and even that is before 1st trimester is over).  I'm not a big drinker but usually have a glass of wine.  My MIL will be VERY suspicious if I turn down a glass.  What excuses do you use for nosy family without spilling the beans?