My MIL has become so overbearing and naggy as can be since we found out my wife is pregnant...?

I don't know what to do with my MIL she has become so overbearing and Fuq'ing nagging the chit out of me and i am starting to reach my limit. I tried telling my wife tonight but she said its only because this will be her first grandchild and that she loves me and she always has and that its just a phase cause she is so excited and everything. Well my Inlaws were over tonight and i asked my wife to get me a drink since she was already up and my MIL got raging pissed at me and went off screaming and yelling at me. I got so mad but i didn't yell back i just removed myself. I don't understand why my MIL has turned into such a witch my wife and i are 26 been married 8 years and it was perfect till now. What do i do? What can i do? Advice?