How to deal with girlfriends crazy hormones?

My girlfriend is ~5 months pregnant. I know hormones give women hardcore mood swings, but I don't know how to handle it. She gets mad for very very unreasonable reasons, and is blatantly mean to me. Then gets mad at me because I'm being mean to her. We're in a long distance relationship right now so we skype, and when she is grumpy I try my best to cheer her up and make her laugh. But she gets irrationally mad at me, and its starting to crack me. I am currently trying to discuss things with her and she is maaaad. How do I approach this, those of you with experience?